My (never complete...) TUBE TESTER COLLECTION

Last Update: 22-Okt-2014 17:55

Before you read the rest....

When you are here, you probably are interested in tube testers in some kind of a way. Same as me! I remember I threw away a shoe box full of used ECC81, many Mullard and Philips, using a defective tester (in 1988) and they tested all in the "?" range. I didn't have much knowledge about tube testers. I I thought an old tube tester is like an old multi meter. So to say not extremely accurate, but still useful. Later I learned the old tester was indicating too low value for all tubes, and probably these tubes were all fine. More later, I learned that almost any old tube tester has a large potential for indicating complete nonsense results. It is amazing how completely wrong they can read, and you may not notice. That is because you have no reference. A voltmeter you can plug into the mains, and at least within say 8% you know if it's good. With a tube tester what will you do? You stick unknown tubes in it.

Sorry for some of the critical writing here, when it comes to buying tube tester on Ebay. Also for me, there is sometimes no alternative for having to buy there. So I prefer to write about things as they are, and in some cases it is beneficial for all of us, to have good understanding of the (real) habits at Ebay. My opinion is, Ebay is the most unreliable buying place for a tube tester.

This page has grown a bit larger than I expected. Please note this: This website is commercial one, meaning I live from it. I understand you probably have many questions, since you are not reading this page here for nothing. Still I need to take care of orders first, so I have little interest in answering emails just give free technical support. Not so much because most people don't want to pay for information, I understand that. It is just I don't HAVE the time to take care of this for you. So for any questions about a broken tester you bought on Ebay, or somewhere else, just post it on the Jacmusic tube tester forum. When I have time, I may even answer it myself perhaps, and like that the information doesn't get lost and is helpful to all of us.

 

TUBE TESTER FORUM
For questions of how to repair a broken tube tester, we advise to use the Tube Testers Forum. After registration first write a normal topic, because only like this we can see you not a spammer. After this, you are released for free posting.

 

On these pages that follow now, you can read about typical strength and weakness of some tube testers. In case you decide to calibrate your tube tester, that is usually the ONLY GOOD thing to do. Feel free to ask some advise about it, but please be a gentleman, only ask things you need to know prior to buying the calibration tubes, if you have the intention indeed to buy those. And if you really do, you can just as well ask afterwards. So we try to do it in that order ;)

Why to use a vintage tube tester?

The answer is simple. They offer functions new made do not have. Mainly the new made testers work digital, suggesting precision. However that is very probably not the case, and not what you need anyway. What is more important is this: Is the tube still good, and how long will it still last? Modern testers like the AT1000 give no clear answer to that. So fine, you know the plate current is for instance 80%. So what? That was not your question. You may reject this tube, because 80% is not 100%, but you and the digital tube tester make a bad team, if neither of you don't know when a tube is bad or not. Put the same tube on a Funke W19, and it says. "20mA. Good starts ar 12mA". Look! That is something down to earth. So the tube is not bad at all. Put the same tube on a Hickok and it will come way in the green. Wow.... and you were ready to reject it. Such experiences I made many. Or the (not so) famous AT1000 will say the tube is at 100%, so you are happy. You put in an amplifier and after 10 hours the speakers say: "CRAX&%&%$". Well, you better should have passed it through the Hickok or AVO leakage test sequence, that would have spotted that leaky electrode. Or, you dig up some radio tubes from the 1940's and the new made tester -OF COURSE- doesn't have the sockets for it. All in the end, you must see of a vintage tester as a concentrated amount of experience of those old tube guys, you're buying this experience along with the old tester. So if Hickok found out exactly this or that setting to reject a 6SN7, you can never replace that by a plate current measurement, not even telling you if the tube is ok or not. I have learned to trust a test result from a vintage tester which is a good condition, more than anything else. I have a fully restored Hickok 750. When this tester says: "Bad tube", well than that's what it is. At the moment I see many people returning to those good old analog tube testers, and it's the right thing to do.


CONTENTS

  1. Calibration set
  2. For Sale items
  3. How to test tubes, on various testers
  4. Digital Testers
  5. About tester accuracy and errors
  6. BUYING ADVICE, and why EBAY is not a good place to buy a tube tester
  7. Tube Tester Collection
Ratings, at "Conclusion" Part: See here

 

1) Perhaps this is the best place to advertise our calibration tube set.

 


NOS tubes


Leakage Tool


Reference Card

TUBE TESTER CALIBRATION TUBES.

Order Nr: 624-014-55
See price list (appr. line 639)

What you receive::

  1. Guide to tube tester repair and calibration. 45 pages in color. Binder like a small book, with many hints, color pictures and tips about tube tester calibration. This is not available anywhere in the internet. We see someone selling a similar item on Ebay, on DVD for a crazy prices. This material is partially copied from our website. You get it for free with the calibration tubes. Also for sale as a book only.
  2. Test Tube1: Philips USA NOS 6922, Original military Box
  3. Test Tube2: RCA USA NOS 6L6 Steel can. Original Red box
  4. Test Tube3: Russian NOS 6SN7, Original box, or white box
  5. Test Tube4: Russian SQ NOS 6L6 with 10% heater voltage tolerance, Original blue box.
  6. Leakage test tool. Instructions how to use it, is in the manual
  7. Tube curves, color printed, to check your tester at any point you like
  8. Quick overview of all test data of those tubes on a plastified card.
  9. Free email support about how to use those tubes.
  10. When it is finished, later, we add a free DVD, with all tube tester manuals, as we have on file now (not available yet)

6922, 6SN7 and 6L6 RCA tested on a range of perfect tube testers, and documented results. 6L6 Russian is complimentary, this tube is to replicate the 6L6 RCA. (Instructions included). So the Russian 6L6 has no test data with it, and the RCA 6L6 is fully tested on all testers.

Guide to tube tester repair and calibration.

45 Pages color printed, in binder.

Read some part of it here.

Order number:
624-017-37

Price:
See price list


 

The use of calibration tubes.

You can say at every AC Tester, you simply need such tube for calibration. There is no other way as to take a known tube, and set the tester's reading for that value. Even so, from Hickok you could even buy them, but that is long ago. Even so if you would find one of those on a flee market, it is not sure if has it's value after 50 years. At Hickok they used the RCA Steel tube 6L6 for this. At AVO they recommend smaller tubes, such as ECC82 or 6SN7. Also for any DC tester they are a safe ways to verify the tester with a range of tubes, and check at several operating points. Also important it to check the leakage function of your tube tester, you need the leakage test tool. First the tester must be able to detect leakage in a reliable and predictable way. Then, if this function is verified, it also proves the deck with the sockets is not leaky, since any problem here would false any test result.

Where are you now?

Most tube collectors have a tube tester, that was not serviced for 50 years. Those testers that have serviceable parts inside, are likely to be off calibration in a terrible way, it shouldn't come as a surprise. If the tester was stored in a basement or a garage for the last 30 years, the components usually suffer from this very much. Capacitors have gone leaky and carbon resistors have internal cracks, and higher resistance resulting from this. This condition is where most tube tester are in, specially the Ebay ones. However most things inside the tester can be repaired professionally as long as the basic material is good. With this I mean the meter, the transformer, and wiring. With an unknown condition tester comes first VERIFICATION, which means you check a tubes with known values, and the tester should reproduce this within it's specified tolerance. Then, normally you find larger deviation than that, and you can do a calibration attempt. This means you calibrate the tester with a known tube. After this, some other types of known tubes should also indicate correctly, which is not necessarily the case. If you calibrate the tester for a 6L6, next you need to try if it works well with a know 6SN7, and then 6922. So this is what the calibration tubes are for.

Suppose you find out then, your tester has some deviation even after calibration, you can still decide if you want to keep it, or repair it.

The the tube calibration set we sell, has following contents:

  1. A supreme quality METAL CAN 6L6, NOS RCA. It was exactly this type of tube, that was for sale by Hickok, long ago. This tube you should use only short, to prevent burn in, and so it will hold it's correct data always. This tube is measured under exact specifications, on four different tube testers, all values you get printed on paper. The average is calculated, and printed on the tube. This is the reference tube of the calibration set.
  2. A supreme Quality Russian 6L6, of a type made for instruments. (Page1- Page2). From this tube, you make a replica of your reference tube. It is explained in the calibration manual how to do this. This tube you can use for as long as you want, and simply re-calibrate it yourself from time to time, using the RCA METAL CAN reference tube. Then put the RCA tube to rest again.
  3. A Russian 6SN7 also intended for instruments
  4. A USA 6922 with military specification. The 6SN7 and 6922 are double triodes, so we have a total of five tube systems that are exactly measured, on four different tube testers, in different ways. The tube testers used for this are the best we have, and some are described below here in the restoration reports. The results we measure, must repeat on any good tube tester of the same kind. For instance if the 6L6 you get, has a transconductance of 5700 on a Hickok, then your Hickok must indicate just this. Deviation max 5%. Also in the case your tester reads 5400 "only" you know now, it tends to indicate lower than normal, and you can work around nicely with that.
  5. A simulator for various kind of leakage belongs to this tube set. This is has known resistors inside. Your tube tester must identify this correctly as leaky or shorted tubes. The values are chosen such that the neon lamp of your tester will shown three conditions: "just on", "just off" and "burn very bright". You have to check for all three conditions. (more information about this product here) Remember heater to cathode leakage is the #1 cause of tube hum for tubes that test "good" for the rest of it. So you sure want the tester to be reliable on this point.
  6. Individual tube curves of the Steel can RCA 6L6, the 6SN7 and t he 6922. So you can check your tester at any operating point you like, any tube you need, and from the curves even derive the transconductance at a random operating point by this formula: Gm= (Ua1-Ua2) / (Ia2-Ia1)
  7. Quick overview of all test data of those tubes, on a plastified card.
  8. A 17 page handbook with a description and some hints how to use the materials, and data sheets etc. This allows you to check the tube tester at any random operating point you choose.

---> Also you should click here if you want to calibrate your tube tester <---

Customer feedback from Sweden, for the calibrated tube set (Dec 2009):

Hi Jac,

Now i could verify with the 6P3C (6L6) and the value was :  Ia 75 and S 5.7 I got   Ia 74 and S 5.8 That's AMAZING 
Also checked the Anode voltage by A1 and ground when testing the 6922, i try to put in on 90V and on my RMS multi meter it was 89,7..!! So I'm very satisfied. THX to i i sold my AVO mk4 for the L3-3. I will always THANK u for that!!! Mine was calibrated in Ukraine, and i tried so hard to get instruction but i give up due to language circumstances.
 
MERRY CHRISTMAS und Auf Wiedersehen!
Matts

* * Scroll down to read about tube testers! * *

2) FOR SALE ITEMS

TUBE TESTERS FOR SALE

I am selling off some testers from my collection to free some space. Once these are gone, I will have not others for sale. Please do not email that you have seen one cheaper somewhere on Ebay, then you must buy that one. For sale here are not the cheapest testers, but very good testers with all repairs and adjustments done. Actually with Ebay prices going crazy for a tester without logical reason, it can also be that you have to pay more at Ebay for a tester sold "as is". Relation between price, quality and availability is random at Ebay. For instance I have been looking over 12 years to buy a SOFIA. The seller was a very unpleasant person, but the tester was ok, so I buy it from him, and good bye to him. On the other hand I see useless tube checkers sell for 290 Euro, which is 250 Euro too much. (like this one here)

Funke W18 Additional Box for Military tubes - FOR SALE

This box belongs to a Funke W18, and it can test almost any German military tube. The box gets plugged into the AD1 socket, and then you have another 34 sockets available. There is the original set of special cards belonging to this box, from 1200 to 1310. These cards fit only on the W18 tube tester, and the card numbers are found normally in the blue book. Mint condition wooden box, appears unused. Inside wiring like new. Connector plug with AD1 plug on it, original condition, can be used just normally as it is. Needs no re-wiring. The first card (1200) was on the outside of the deck of cards, and is a dusty and dirty, alls other cards inside are clean.

Export Price: 150€ without VAT tax
Europe: PRICE 178,50€ with 19% VAT tax.

--->>>>I have also the W18 that belongs with it, it is complete, but needs repairs. Please ask if interested.

 

 

AVO Mk4 - FOR SALE

I have several n my private collection, over the decades a lot of stuff piled up here. I am getting older, and I am clearing my collection. I want to keep only one, just because the Mk4 has some specialties of it's own. Leakage test is so fabulous, and also you test almost any tube, or set up new tubes just by using a data sheet. It can do up to 400V and 100mA. For that reason any tube company would at least need one. They are all sold without any problem whatsoever, new calibrated, and fully checked up.

So here is the next one: This is the history, as I remember it: This unit I bought as a good and calibrated tester, from a customer of mine. It was kind of ok, but precision was dissapointing with specific tubes (though not very much dissapointing), and yet very good with some other tube types. So I decided to keep it, as base quality was very nice. Then after some time I started the restoration, and it appeared the panel meter had lost 10% magnetism. (So 10% too low reading). Now this CAN be repaired too, but luckily I was able to dig up a replacement meter. (Please don't ask me for another.... they can NOT be found). Obviously one of the previous owners had "calibrated away" the panel meter problem, and even touched the (non-user) factory calibration of the grid wheel to get this job done. It didn't even work very bad, but not satisfactory for me. The panel meter sensitivity must be within 5%, and the meter impedance within 1.5%, writes the factory service manual, or you can not calibrate the tester well. So with the new meter, calibration went smooth. The Noval socket was replaced with a new one, and the whole tester was taken apart, as I always do, when restoring one. So I could check the potmeters, and the switches, etc. With the replacement meter, and new factory calibration it works just perfect. Some small work was done, check the pot meters, etc. but that was nothing very special, and there is no log of that. So this one is mostly all original inside. I still use it occaisionally, like I do with all testers, to keep it in good shape.

This is now a fully restored + calibrated AVO Mk4.

What you get:

  1. This fully checked up and new calibrated tester. Nice optical condition, no damaged hardware. Back off is totally stabile.
  2. Original AVO Data Book. Complimentary, condition not nice, some pages loose, but complete, and at least you have it as collectors item. So you get this for free at no cost.
  3. Printed in a nice binder, all best quality copies I have: Latest Tube Data book version, Fast Operating Mode (the card that is in the lid), the Operating Manual, the Service Manual. And if interested, you can get electronic copies of all this.
  4. The calibration tube (6SN7) that I used to calibrate this tester, and the computer test report belonging to this tube. So you can pick a random working point from these tube curves, then set the tester for this, plug in this 6SN7, and you will see the tester measures this tube exactly as it is. This is an amazing quality tester you get here!
  5. Guarantee: The tester is guaranteed to be in 100% good condition when you receive it, with three months additional guarantee in all work done.
  6. Free support by phone, skype or Email, to get it going when you are new with the AVO Tester.
  7. The handbook: "Guide to tube tester repair and calibration - Color printed, in binder.
  8. Here is an example of restored AVO Mk4. Check report here

Price 1900 Euro without VAT Tax, for export.

Price 2261 Euro with VAT Tax, which means European communcity countries.

Swedish Handbook for AVO MK4 + Swedish quick Guide, the plastic card for inside the lid.

This is a curiosity, I never saw a translation. Very nice quality, the plastic card was never mounted, so it is like new. The handbook is in a nice blue cover of the Swedish Radio. Original printing, no copy.

 

Export Price: 20€ without VAT tax
Europe: PRICE 23,80 with 19% VAT tax.

3 How to test tubes, on various testers

Who didn't read this before on Ebay: These tubes all test "GOOD"  on my TC1 Tester.   Wonderful, that makes them more expensive. Right?   Well,  it's better than nothing,  but  that's about it.  Because, what I personally would like to know for HiFi, is this:

  1. What lifetime is left in the tube?
  2. How close are they to the original factory data?
  3. What about good Vacuum, good isolation?

Keep apart the categories of the tubes to test. These are: 

  1. Rectifiers.  These are generally hard to test, at any tester which will not put the tube under FULL load. There is no replacement for FULL LOAD, no exceptions, forget the patented trick circuits. So full load is for instance 250mA for a 5U4G tube. It has to give this DC output current without loosing too much voltage, nothing more and nothing less.
  2. Small signal tubes. Here the question is: Is the bias current correct? Only then it will bias correct in the amplifier, and only then it can give the right amplification at little distortion. Another way is to test the transconductance, which is a pretty safe way to say something about the use condition. There is one dangerous assumption, that is this: The tube was biasing good when new, and transconductance was good when new. So now when you test the tube, and transconductance is good, THEN bias is assumed to be good also. (this is an assumption only, and will not be true in all cases). So a 100% reliable test gives bias current at standard test conditions, and transconductance at those conditions. Note, many tube testers use home brew test conditions, like Hickok. This is works in most case, but is not ideal.
  3. Power signal Pentodes. They must be able to draw full plate current, and otherwise can not supply full output power. So you have to TEST those AT full plate current, and nothing else. Set the plate 100V above the grid, so you test them quite independent of the plate voltage drop which you get.
  4. Power signal Triodes. These are the hardest to test. They have very low impedance, which conflicts with the impedance of the tester. Hickok recognizes this by leaving out the 300B from most roll charts. Ok, this is honest.

The a problem comes, when you want to know the quality of a used tube. There was never a general method published for this by any tube manufacturer.   This was always left up to manufacturers of tube testers. So... it means: Many tube testers, many methods. 

4) Digital Testers

I own a few digital testers myself, and it is a category for themself. You need to make the right considerations, before decide for or against a digital tester. Let me list up some of the advantages and disadvantages here.

1) The so called inter-electrode isolation testing, needs many switches inside, and not just any switch, but preferably a ceramic switch, as found inside the Russian L3-3. With digital testers, this is always a weakness. Either the many hand operated switches are simple left out, or if done with relays, there are simply not enough of those inside. Actually I know of no digital tester that can do inter electrode testing between all pins of any tube. Some can do cathode to heater leakage, and that's it. Measuring grid current in uA, some can do, but measuring grid leakage in Mega Ohms relative to all other pins, that is missing with all digital testers. The beautiful way this is done with the AVO Testers, differentiating even between hot an cold condition is an example of mature product design. Alone the analog circuit that is behind this would be extremely hard to reproduce digital, as it works with a high AC Voltage + very high resistor in series. This is is the ultimate way that can even detect corona leakage. Note, the inter-electrode isolation testing gets more important for the future. We will be dealing more often with older historical tubes. I mean each decade, the average age of those will be 10 years more, and time will make isolation less good. Also, we will be dealing more with new made tubes. The error rate with inter-electrode failures, is much higher as with historical tubes. Chinese tubes have a bad reputation for this. Inter-electrode resistance is very high in general, but many failures. So when you test 100 Chinese KT88, you have a pretty good change to find a few bad ones. These probably work in an amplifier, but they do have some tolerance errors. Whereas with Russian tubes the error rate is lower, but generally the leakage by itself is higher, and the trend for newer production is not good. So either way, this function gets more important. With the AVO testers, due to the highly intelligent test circuit, even electron emission of the heater itself without plate voltage can be measured this way. Though this is not described in the AVO manual as a measurement, it is said at least at which settings this is indicated. Real specialists will study this option, and learn to estimate it. It is an illusion to find this ever in a digital tester.

2) Tube sockets. Have a look at the test deck of a AVO Mk2...4, and you have a feeling of what possible sockets one may need. The test book of AVO is filled with hundreds of pages test settings in small printing. The value of this database is enormously. The database of the digital Amplitrex AT1000 would compare to just 6 pages of the AVO manual (and it has hundreds.). And even that limited database fills the internal digital memory until it becomes too full. Besides it has no full possibility to connect to any tube pin. So even though the tester has an octal socket, it can not test all of the tubes. Not so with AVO or Funke. Just take any tube -whatever- and you have the socket, you can connect it any way you need, and you have the settings in the book. This uncompromised completeness is an illusion with new made testers, as far as I write this text today.

3) Overload / Shorts protection. Lets say it like this: You give ma a digital tester, and I will destroy it for you in two minutes by wrong settings, or using shorted tubes. With a good analog tester that becomes a lot harder to do, but of course it is possible as well.

4) Hardware and Software aging. A particular digital tester is always nice for the moment, but sooner as you expect, the technology gets old, and repairs may become nasty or impossible. If it needs installation on a PC, the Microsoft Gods always try to make your old hardware obsolete. So will it install under "all versions" of Windows? If the maker says yes, does that also mean future Windows versions? It may well be in 20 years you can only run it on a dirty old "Windows 8" computer, because "Windows10" or whatever new version refuses older programs to install. We have that now with the Sofia digital tester, which hardware and software COULD run under Windows, but just the Microsoft Gods do not allow this option.

5) Voltage, Current. Make sure, the digital tester can do the same as a good analog tester. Can it heat 20Volt tubes? Can it do -150V on the grid? Can it supply 500V plate? How about the screen? Can it do 250mA plate current? Can it heat power tubes with 50 Watt? Can it meaure 0.5uA leakage? Can it measure 10 Mega Ohms leakage ristance (Are you sure??). Is the leakage tested under high voltage? In both directions, as will naturally occur when you test with AC? Can it test any heavy rectifier under real load conditions? Can it also test the 1mA rectifier of your radio detector circuit? Can it test Voltage regulator tubes? Can it pentodes triode-connected? Can it test the oscillator-mixer tube of your radio? Can it test magic eyes? I hope I forgot nothing here. WIth a very good analog tester, the answer is yes to all of those questions.

6) Good-bad indication. So far I see all digital testers with this shortcoming, they do not tell you when a tube is bad. That is because the writers of the software, either do not know how to test for that, or do not have the time and resources to test thousands of known to be good and know to be bad tubes. You do get a precise number of transconductance. Then you say, fine, but is the tube good or bad? You still don't know. This is where the good old Funke W19 is my top favorite, but sure also the Hickoks. Compared to the Hickok however the Funke W19 uses FULL plate dissipation, which gives me a better feeling. So all digital testers seem to be missing this #1 feature of a tube tester. They do not tell you if the tube is good or bad.

7) Precision. Of course digital testers are the winner here. Keep in mind though want is a need and what is a want. So you want 0.5% precision, but do you need it? You can only answer that for yourself. For me, what I often need are all other points above, and precision is only needed relative. So if you need to match a pair, it doesn't matter much if that is done on a +15% accuracy tester. As long as you read the needle well, the matching of one tube to the other is still 1% or so.

Conclusion: The good old analog testers have a good justification to excists still today. Of course digital testes are something very nice.

 

Clicke here for a compare of digital tube testers.

 

 

 

 

 

Here are some ways to test a tube

1) Plug in a brand new tube in your amplifier, and see if the function improves. 

This result can't be denied!  This method was used by many service technicians!   The tube manufacturers had special cases for that for service man, with a collection of new tubes, one of each.  If you have no other way, take this way! It is a very good one.

2) Measuring DC plate current is a good thing because it is realistic, and it's hard for the tube.  This is no job for a low cost, or also not for a "patented" tester. There is nothing to patent on a normal, straight forward DC parametric tester, and this is the ONLY 100% safe way for power tubes. So once the tester has patents in it ... I get this "no no" feeling.

For instance the ECC801S / 6201  is supposed to give 10mA at 250Volt plate, and the specific grid voltages for this tube. It is "good" when not higher than 14mA and not lower than 7mA.   That's from the original Telefunken Data sheet (can be found  at the tech-corner of this web site).   The end-of-life is below 6mA, or when the original value it had when it was new, has lost 40%.   Now that is a very clear specification :) So of course THIS is what you like to verify, and the very moment the tester has a patent, it means it is NOT testing this way. I know if no testers that are an exceptions to this. So, also not AVO because they are patented too. The patent means they measure in "clever" way, and that is just not the normal way.

The GE Data sheet of the KT66 simply says below what current the tube is bad.   Unfortunately these are the good exceptions,  and most tube manufacturers avoided that question like monkey plague.  

When measuring real DC plate current, you need very precise and heavy electronics,  these tube testers are expensive, and may need calibration or periodically verification of the  tester.  In the instruments world the definition about calibration and verification is a reversed one.  Please take good note of this. It means when specified NOTHING, the instruments needs yearly calibration. If it says it needs a calibration every five years, then this counts instead. So no information = Yearly calibration. This the way the world of instruments is defined. So if your tube tester is from 1965, nothing is written about calibration in the manual, and it was never checked ever since, FORGET the results. It missed the calibration every year ever since 1966.  Verification is a process which must be specifically ALLOWED by the instruction manual. So when not mentioned, it is no good way to test this tester. Verification means you compare the result to a know tube, and when ok, the tester is ok. VERY FEW tube testers are so good they can be checked that way. For instance Funke W19 can be checked that way.

When is a tube good or bad?

Generally it can be said a tube is bad when the original plate current is below 70% of the initial value for European tubes, and below 60% for USA tubes.  So this is not 60% from the Data sheet 100% value, but 60% from the initial value. The initial value may have been lower than the 100% value or higher. Hard to say what the initial value was after many years. The best is always to mark it on the tube. Otherwise you have a dirty method here. To give an example: a tube has for instance a 100% Value of 100mA, by the Data sheet Suppose the initial value of YOUR tube was 70mA, when it was new. A European tube may drop down to 70% of that, so 49mA and is still good. But.... suppose the initial value was 140mA, then 70% of that is 98mA. Below that the tube is worn out! So you see how important the initial value is. Always mark it on a new tube when you know the value.  Has the initial value got lost, you have to guess it. So quality tubes have the initial value written on the box.

3) Measuring Transconductance is good, because you can construct good tube testers,  with little electronics, and get useful results from that.   These often need no or little calibration, or just verification.   So verification requires a calibrated tube, or another tester of the same kind to compare the results.  However.... Testers that measure transconductance with little electronics are not never accurate with ALL tubes, and that's per definition. So the Hickoks are typically calibrated with a 6L6, and you can fully trust the readings with any kind of similar tube, like KT66 or KT88. However they are not capable of testing tubes like 2A3 or 300B under real life conditions. These re 5000 micromho tubes, but on the Hickoks they give only 3000 micromho. If they do on a Hickok, they're fine. In real life such tubes are bad. So you see my problem I have with any patented tester whatsoever.

What is not so good, with "Transconductance only" testers, is the unknown DC conditions for the tube under test. I have many Hickoks, and I find that a "bad" tube on by those testers is definitely bad.  These tester makes no mistakes with that.  But how it came to that conclusion is unknown.   If you do not want to know why a tube is bad, but you are only interested if it needs a replacement, a Hickok is THE tester.

The ideal way to measure transconductance is with an AC (audio) Test signal, and adjustable DC and original Data sheet settings to go with it. Very very few testers work like this.  Almost every tester has i it's own way to avoid this. Reason is, as said before, expensive electronics.

Some very good testers however, are the higher class Hickok testers. These perform a real transconductance measurement, with a (known) Grid bias voltage, put a known AC signal on the grid, and from that measure the real AC plate current. Do keep in mind ALL Hickoks work with AC wave shapes, that represent equivalent DC voltages, and this limits the precision, no matter what you try or do. A better method for this, is not using the mains voltage a signal, but a higher frequency from an oscillator. Why is that? You may say you can also measure transconductance at 50 or 60Hz also? The answer is: No you can not measure that precisely at the mains frequency. Reason is, if the tube is humming (so it has a defect) the hum signal will be a part of the plate signal. So such the tube will read better than it is. The Russian L3-3 uses a 1400 Hz sine wave at the input of the tube, and a 1400 Hz selective Voltmeter. This is in fact a very band pass filter. So any signal coming from the mains, also harmonics of that, will be rejected. Also distortion and white noise of the tube is not added to the result, since only 1400 Hz is measured, within a few Hz only. The second harmonics is 2800 Hz, and filtered out. This method is the one and only true measurement of transconductance.

I found almost no tester that can accurately measure the transconductance of larger directly heated power tubes like 2A3 or 300B. The testers I have, so far the only one that produces an EXACT and fully correct reading is the Russian L3-3. All other analog testers produce values that are quite imprecise. Also the great and highly valued AVO Mk4 doesn't come near. Wisely they left out the 300B of the AVO manual. Also most Hickok roll chart avoid mentioning the 300B. I found out the reason for that, is the too low plate resistance of those tubes. There is a hint about that in the AVO manual, but this hint is written in such a way that you will not understand the real meaning of it. What they mean at AVO is: Forget the results for all tubes with low Rp. The Hickoks also can't measure such tubes accurately if you ask me. Those Hickok testers that can't do it, also don't have the 300B in the manual. If you do test it, by simply put it in 2A3 and set the filament to 5V, you get wrong results. So it will read 3000 micro mho for a tube that has 5500. Also for your 2A3. But... who knows the real Gm of a 2A3 before testing it ...? So nobody finds out, and nobody will complain. The digital tube testers AT1000 ( we have three) is good, but the L3-3 is better. Just not as convenient, and the AT1000 software is a bit crude. The Sofia software is extremely delicate, like you can point with the mouse at any position of the a curve, and you get the three main parameters in one window, for that particular point. (G,. Rp and gain). Well for me, the L3-3 beats any tube tester I have worked with.


4) Load Testers.  With this test,  any tube is connected as a diode, and it is tested how much current the diode can make flow through a load resistor.   These testers can be build almost without electronics at all. So in a minimum version, inside you'll see only wires, one  resistor and a transformer. They're  cheap to make and  easy to use. With nothing inside, nothing can get defective. Most radio and TV repair men had them. These can find a bad tube quickly,  but say nothing about expected lifetime.  So it told you what tube to replace to get your TV working.  These do pick out bad tubes. So if that's all you want to know, this kind of tester what you need. Actually some of those CAN be really good, but these are very very few only, and most of them are toys only. Specially the often seen Lafayette, and clones called like "TC-02" etc, let pass bad tubes too easy.

Click here to read about the accuracy of a Funke W19 tube tester.

SHORT OVERVIEW OF TUBE TESTER FEATURES IN EXEL FORMAT: -> CLICK HERE

“The point in question now is whether the emission or transconductance test is the best.  This is determined in part by the circuit in which the tube is to be used, in case of an RF or IF amplifier tubes, the stage gain is proportional to the transconductance; this the Gm test is the most important.  In case if an output or power rectifier tube, it must be capable of supplying large amounts of current; here the emission test is the most important”

From: Fine Points of Tube Testing. by William F. Burke, Consulting Editor, which appeared in the 1958 Test Equipment Manual.

 

4) About Tester accuracy and errors

There four ways to deal with errors 1 ) Prevent errors, by thinking ahead. 2) Learn from other peoples errors. 3) Learn from you own errors. 4) Not learn from errors, regardless who makes them.

A tube tester is a very professional instrument, but many unprofessional "tools" were sold as instruments, to users that never found out about it. So in a way everybody was happy. Today this has not changed very much. It is amazing to see the happiness level sometimes with lousiest testers. On Ebay I see people out bid each other for testers with new appearance, some rare cases NOS and in their original box. Then you see such junk as this one here on the left, go for 300 Euro. When pictured with a NOS EL34 Telefunken, the further the needle is in the green, the higher the bids are on Ebay. Clearly a very high read, is "the" expectation of all users. Well, and I am not the only one to have learned this. 50 year ago, equipment makers, already knew this of course.


Here is a link to my page about tube tester accuracy. You should also try the link there to MIT professor Lewis's youtube video about accuracy of measurements. Part of his lectures were even broadcast on TV.


This young man is Professor Dr. Barkhausen. He introduced in 1918 a way to put the tube parameters into a convenient formula similar to ohm's law. Originally this behavior of tubes was discovered in 1914 by a man named van der Bijl, who worked for Western Electric. Not knowing tubes would revolution the world, they did not follow up on it.

The main formula is:


D= 1/Gain
S = Transconductance (G)
Ri = Plate impedance

 

5) Buying a tube tester on Ebay

Have you already been cheated with a tube tester on Ebay? Welcome to the club!

Ebay is not the best place to buy a tube tester. When prices are rocketing, there is little interest to sell, and high interest to buy. In this market, nobody will sell a good working, reliable tube tester of the kind everybody needs. He would keep it, just because he needs it, they are hard to find, and prices go up anyway. That's because they're almost impossible to find in very good condition. What is for sales is the whole category of testers that are of little practical use, or seem impossible to calibrate, expensive repairs coming up, fungus, or other reasons, to dump them on Ebay. So don't believe you're going to be the lucky guy, paying only a low price for a fine tester. Also don't think worst case you get one that you will able to fix with some basic knowledge. F-o-r-g-e-t about that. People buy them, try them out, find the problems, and some weeks later you see the same tube tester again on Ebay. I have only very negative experience on Ebay. You will never find a tester that you can repair with some glue and a piece of wire. I thought so myself too, but that was a long time ago. Typical problems are partially short circuited transformers, bad panel meters, defective rotation switches for Funke and Neuberger. All kind of things that were hard or impossible fix by the previous owner makes the thing land on Ebay. The seller always tries to appear untechnical, so he wants to put you in the "lucky guy" position. Then when you find out he sold you a piece of junk , he is prepared with excuses. The Ebay text was formulated with great care, and end up as the "unlucky guy. The seller has been trying like crazy to get it fixed, and gave up, and his friends too. With the crazy prices on Ebay, he gets the enlightened idea to sell it, and buy another one for the same money. Then he tries to be the lucky guy, and worst case he exchanged a bad tester for another one. So he can't go wrong. And nooo... I am not paranoiac. I have just a bit more experience with tubes testers.

Here are the observations I made:

  • When the tester is sold as "defective" they bring about half of what is reached for a "good" one. When they are advertised as "from my uncle who passed away" and the seller pretends to be non-technical person, they go for almost the same price as a very good one. It seems passed away uncles leave only fine testers, that is the myth. In reality, you buy an item that is untested, unknown condition, and no return. That's what it is. If it was offered like that, prices are only half. Also you are much recommended to read the other feedback. I bet you find items in there, definitely showing the seller is technically very skilled. Be honest.... would YOU sell a tube tester untested? I mean, you can at least try if it is fine, and you get a higher price. So if person sells an untested tester from his passed away uncle, and at the same moment sells all kind of tested tubes, tested with a Hickok tester. This may seem stupid to do, but they do it, and I see such auctions often.
  • Forget also the testers that spend 45 years in a garage. You better hope it is not so. These are dead meat. They can't be fixed with contact spray any more. The Ebay seller sells it as "found on the attic" and you think you make good buy. Ha ha! When you are really diving into the defects, you will even find out WHY somebody put this tester asleep 45 years ago. Then today, after you repaired the rusty switches, and exchanged the fungus capacitors, you will come to the same conclusion as that person, 45 years ago. There is a non repairable defect, that was the conclusion then and it is now. Only... now it is rusty and all contacts are bad. It happened to me several times! So I give negative feedback to such without a warning. They are totally upset when that happens. It seems to be normal on Ebay when you cheat someone, and he finds out, he just takes the item back, you get the money back, and you give each other good feedback. Well I' am old fashioned, so if the sellers cheats me, he gets a negative, and that's it. In the case you want to talk, having a few negatives in your feedback, makes even a potential fraudulent seller treat you a bit more respectful.
  • Don't take a tester with a cut off mains cord. It means, long ago for someone the mains cord was worth more than the tester. Also don't take a tester with the deck plate screws missing. It means, long ago someone thought it wasn't worth putting the junk back together.
  • Take only a tester that is guaranteed to be OK, and tested, and normally used by the seller itself. It won't be cheap, and still the seller knows better than you why he sells it, but you probably get a working tester.

SO WHERE DO I GET MY TUBE TESTERS FROM? I get them from people I know, and for the rest of it, I am not buying from strangers unless cheap. When buying on Ebay, I only take sellers with 100% positive, and I make the proposal I can try it out, and when the thing is not as described, I can send it back. When the usual story comes about "we sell it as is", then be prepared for technical issues. So just walk away, or pay 50% only.

What would you say when you get offered a 10 years old car, from somebodies uncle, who just died, and the car is probably good of course, and all stories sound nice. But: payment in advance, you have pictures only, and no guarantee, and no return. This alarm bell, you should have with a tube tester also.

LINK to Ebay PROBLEMS. Here we go again.

CONCLUSION1: Recommended testers look for instance like this.

Starting with 200$ for the simple ones like Hickok I-177. Then 400..1000$ for the better ones. From 1000...2000$ for such that test at REAL conditions, can test ALL tubes, have all sockets, and have English Manuals. Price reduces by 50% if the tester has clearly no guarantee for 100% good function. (There is no "lucky you" with tube testers, only unlucky you). Price is higher when the tester is overhauled by a knowledgeable person, who documented and guarantees the work done. Price is lower if the tester has been worked on by an amateur.

 

 

CONCLUSION2: Not Recommended testers look like this. Avoid like monkey plague. You can recognize them by the row of switches and miniature size

 

TOP 10 of most popular vintage testers. (Nor for new made testers)
Order is by brand, alphabetic.

Brand
Model
AVO
Mk4
Hickok
TV7
Neuberger
RPG375
Funke
W20
Funke
W19
Kalibr
L3-3
AVO
CT160
ELPO
507
METRIX
U61B
Hickok
539 Series

 

6) Tube testers collection


AMPLITREX AT1000

Having the AMPLITREX AT1000 is having the best we can get, and technologic advantage is what makes our company attractive for customers. So we always use best instruments we can buy. If not, we 100% restore an old one. (see Restoration report about Funke W19 we use, and two "Kali br L3-3" under tube testers) : This testers is, right as I say, "the best we can buy", though I think it is not a very good tester by itself. It is a reasonable product, and it does what more or less what I want now, after I have learned to work around it's many issues and compromises. It can not beat my 1995 Sofia tester.

RISKS. As far as I recall, the Amplitrex 1000 has been introduced in 2004. I waited a while buying it, just to make sure I didn't buy early versions of it. Though buying the later versions, I found several issues myself.

VALUE. The item is expensive, and to have it keep the value, the manufacturer should produce software updates on a regular base. My disappointment here is very large. It has several issues, that would be easy to fix in software, but I can't do this myself of course. I am very unhappy about this. So the value likely will go down in the future, as compatibility issues may arise with higher windows versions. The tester is WINDOWS ONLY, and you don't have the code, and you don't know what this is doing. So if the Microsoft Gods -say in the year 2020 will decide, you need this or that upgraded software version with "Windows11", and you don't have it, you can't install the program on a new PC. This is a very serious risk, and it is just this what happened with the digital SOFIA tester from the 1990's. This is in sharp contrast with some of the very good vintage testers which are more like an investment, than something you need to write off some day in the future. So keep this in mind extremely well. Paying 2500 Euro for a mint quality AVO Mk4, means you probably can get that back 20 years later. The same amount invested in an AT1000, you need to write that off one day.

SOCKETS. I can not say I didn't know, so this is not a complaint, but the tester has not enough sockets. I have a small collection of adapter sockets made myself. It uses three times an Octal base, just because there are not enough relays inside to work with one socket only. The tester WILL NOT switch the heater wires, so the heater is soldered at the socket at a fixed position. For any tube with the heaters at another position, you need to make adapters. So I had to make an adapter to test the 5Z3 rectifier, which is nothing but an 5U4G with a UX4 base. However the UX4 base of the tester is soldered to the DC supply, whereas the rectifier circuit of this tester is AC heated. So there you go again, ANOTHER socket adapter I had to build. Amazing but true... I have found a software way to test 4 pin rectifiers on the UX4 base of the tester, so now I don't need that stupid adapter any more. Please understand I will not hand this out. I think it's the manufacturer's work to provide this to you. I realize they may not know how to do this, but really this is their responsibility to provide solutions, not mine.

First impression. I unpacked the unit, plugged in the mains cable and switched it on. Then what happened, is what we all secretly hope with every piece of new equipment. I needed no manual and I could understand it "by doing". I switched on the Amplitrex, and the large display lights up and comes up with a digital "roll chart". Well, we have seen that before as paper version. So I scroll it down to 6SN7, because I had one on my desk. I selected it, and the tester said: "put the tube in Socket E, and press "Enter". I did so, and the automatic test began before I knew it. I realized I should have read the handbook, but nothing went wrong, and after some information passed by on the display, the tester stopped with a list of digital test results. So plate current, Transconductance, leakage, everything. I was so surprised having this result out of the box. Unbelievable! I took out the tube and compared the result with one of my L3-3 that are reference testers. All readings are identical. :))

Materials. The "feeling" of the tester is much better than it looks on the picture. The case is very good quality and the deck plate is thick and heavy material, and the (few) sockets are good quality. When I see how some of the Hickoks look after so called "experts" have worked with them, this very rugged case for the Amplitrex is a very good idea!

Tube sockets. It must be said, the 9pin socket is a too tight and it damaged tube pins of some expensive ECC88. So you plug in a tube a NOS tube a few times, and the pins look used already. For the rest, tube sockets are fine, and even the (dangerous) metal rivets of the Chinese UX4 sockets have been carefully insulated. Good job. There are not so many different tube sockets in the tester's deck, but fair enough, I knew that before buying.

Noise. Sorry, the cooler fan is definitely too loud.

WARNING. The Grid voltage is measured wrong for Directly Heated Tubes. Half of the filament voltage is added to the grid, and it was not compensated in the software. (Though this would have been very easy to do). So when the tester draws a "-1Volt" line for a 300B, it is in reality the -3,5 Volt line. Same error is made with the normal "Tube Test" page it produces. With tubes of high grid voltage this is no problem, but for tubes with low grid voltage this is a serious problem, since it may have the tubes look "bad" while in fact they are excellent. For instance RE134 has 4Volts filament, and it's a high gain tube. So 2 Volts error on the grid, turns a good tube into a bad one.

Calibration: They do have calibration points inside, but there are several ways to check the voltages from the outside, so you can regularly verify that. Also since we use three amplitrex we can compare one with the other. Mind you, the grid voltage has an internal series resistor inside, so you can only verify the grid voltage with a tube volt meter, or any other very high impedance electronic meter. Or, tap it from the inside, before the series resistor.

Conclusion for Stand alone mode: When you are not so technical, and just need some quick good/bad results, the stand alone mode is what you need, and don't even think about computer control. However this tester does not tell you when a tube is good or bad. This can be real problem for non-experts, and you MAY want to prefer a good old Hickok with a red-green scale. So with a Hickok the red-green scale is really reliable, I can tell you so. The Amplitrex says something about Emission in percent, and Gm in percent, however it is not testing Emission at all, but plate current and just calls that emission. Which is a mistake in the software. Furthermore 20% below average Gm is not so bad as long as the tube heats up fast, and plate current is strong. Vice versa for low plate current. It is no problem when Gm is above average and heat up is fast. Some factory-new tubes can be that way. With some understanding of tubes, the stand alone mode is a very good one. Automatic leakage test and grid current tests are reliable, and switch off the tester in case you're trying to test a tube that is a problem perhaps for the tester itself. In the end you have similar results as with the L3-3, but without all the buttons and knobs and cards and knowledge you need for the L3-3. Here is the advantage of the Amplitrex. It fills a huge gap on the tube tester market.

Conclusion for Computer control mode: This is actually why I bought it. However this function is more difficult to use, and not very self explaining. A problem for non-USA users is, that you MUST set your PC to USA Region, or the software will make errors and/or crash. So used a dedicated PC for this and set it to USA Region. It is difficult to use database programs like Open Office (or worse: Excel), since problems arise where comma's and are used in Europe, where the USA uses semicolons and vice versa. If you ignore this, you mess up the tube data tables, and the software will stall, or produce weird mistakes while drawing tube curves. So to prevent this, I use now a dedicated PC, which I set to "USA" region.

We have now two AT1000 in use, here at Jacmusic. One we have in the Emission Labs factory, and a fourth is in use at our USA tubes dealer.

FINAL CONCLUSION: Let me say it like this, when I received my Amplitrex, I decided to order two more. I think that tells it all. Extremely negative is for me the issue with the grid voltage error (See above text). This item was brought up to Amplitrex, and really a software repair should be a piece of cake. I heard from another user, there is only a patch with the data tables, which is not regarded a decent software repair my myself. It is regarded such by Amplitrex, so we have another opinion about this. Even though this partial solutions excists, I was never informed about it by Amplitrex in the form of an update, or user's letter.

Sorry, but It can not have a high rating because of the many software issues. Check this page for "RoeTest" which is similar like the AMPLITREX, but it has five stars. .

THREE STARS ****

DETAILED TEST REPORT



AVO Mk1

Will describe it later in detail. So far, this one is amazing. Inside is almost no electronics, and since no calibration is needed, nothing can be off-calibration. I tested a 6SN7 that I know has exactly 2.7mA/V at 250V / -8V. The Mk1 reproduces this value accurately. I want to investigate it better, to see how they get this precise results from just two transformers and some resistors. It is the mother of all other AVO's. If you are buying a tube tester, I think this is one of the few that you can buy with little risk. I would say if some unknowing seller says "it works" it is probably good. It has no sockets for 7 pin miniature and noval tubes, but a socket adapter for those existed. Of course you can't get those, and they're always missing. You can easily make the adapters yourself from old tube sockets, and the settings for 7 pin and 9 pins tubes plus settings for ALL tubes in the later edition manuals! What else do you need :)

Here is a nice picture, comparing the accuracy of the Amplitrex AT1000 digital tester, with the Mk1. I get exactly the same reading. The camera was a bit on an angle, but when reading the meter from above it reads 11mA/V. Fully identical with the Amplitrex. Well how about that, with a 60 years old tester. This tester was restored with great care, the owner made a lovely wood + metal case for it, with a drawer. So he put the two in one case. I think he wouldn't have done so if t he tester was not 100% ok. Well it is indeed.

 

In a few words: A fully underestimated tester, secret tip. Sometimes I see people pay 200 Euro for some silly TC-2 useless tester. I don't understand it at all. Then you better pay this price for a Mk1! FOUR STARS ****

AVO PATENTS Zipped files. Very interesting. Package-1 .... Pakage-2



Ebay prices seen:

2006: Good condition: 800€
2006: Defect: 300€


AVO Valve Manuals

AVO Mk2

Here will be placed (later) a re-build report about the AVO Mark 2. This tester can do the same as the Mark4, but it has a little different method to operate it. The principle is comparable to the Mk4. What is better about the Mk2, it has one tube inside which only function is to be a reference tube. So the reference tube and the tube under test go into a wheatstone bridge, where non-linearity of the tube-under-test is compensated with the non linearity of the reference tube inside. This is a very clever system. Also the Mk2 is very easy serviceable, because you can take off the whole cap with just four screws. So you can access it from all sides. With the (later) Mk4 it is almost impossible to work on the inside electronics.

The Mark2 is a very old tester, so they all need some service or repairs before you have them back into instrument condition again. The used electronics are of good quality. No strange components, that you don't know what they are, no rusty resistors, no leaky capacitors, the wiring is still very good after all those years, no signs of cracks or anything. All semiconductors are still good. All rectifiers are solid state, but not Germanium. These are the antique kind of early diodes, with several layers of metal to metal-oxide and very high (40Volts) forward voltage. I took them out and tested them, and they all worked fine after 50 years. I was ready to replace those with new rectifiers, but the old ones tested so nice on my Metrix tube tester. No leakage at all, and very well defined "on" voltage. So I just put them back in.

The reference tube has it's own supply transformer, and the whole unit with the reference tube is mounted on a separate chassis. This sub chassis has only four wires. Two are connected to the mains, and the other two are the connections at which a diode is presented. This diode is then wired into the rest of the circuit. A Very beautiful design., like a master piece, and you can see from this way it is build, that this "tube diode" is the core of this tester. I don't believe the solid state part they used for this in the MK4 is just as good.

The Mk2 has all sockets for any tube that is used in Radio or amplifiers. It can do any mains voltage.

In a few words: For me Mk2 is a better quality tester than the Mk4, and the circuitry of the Mk2 doesn't suffer yet from the "need" of having to use no tubes inside. It's amongst the top-ten testers. The price difference with the Mk4 is not justified, since Mk2 has a higher negative grid voltage possible, and for the rest if it the Mk4 gives no higher precision, and no better or faster results. Mk4 has a more solid case, the case of the the Mk2 can be lifted off very conveniently for service, which is for me more important than nice looks. FOUR STARS ****

Manual of AVO Mark2



 

Ebay prices seen:

2012-Dec 5607 US$
(Auction Nr 370706510866)
(link here)

2012-July 4458 Euro
(Auction Nr 140803614222)

2010 EUR 3.662 Euro
(Auction Nr 370415230702)

2007: "good" : 1600€

2007: no meter
and defect: 600€

 

AVO Mk4

This is the most wanted tester. Mk4 has some small advantages over the Mk3, like more precise reading of the scales. .

The Mk4 is the fourth generation testers of this kind. Very mature, as a the result of many years of development, and all errors of the earlier models were solved.

What is nice about the Mk4 is, you can do almost anything with it, almost any tube. The extremely sensitive isolation test is seen with no other tube tester, and the "shorts" rotation knob is a method worth an extra patent. Unlike the Funke and Neuberger, the AVO M2, Mk3, and MK4 do this with a very simple wafer switch, almost no moving parts, and nothing gets defective. The Funke's do the same, but the rotation switch deck is sensitive to wear out, and needs cleaning. The Neuberger also do the same, but specially the older models all suffer from material detoriating.

Mk2 has the advantage of much higher negative grid voltage if you need it, but the Mk2 case is really a bit too light. The case of the Mk4 is extremely strong, and rugged. It is also a dairy piece of industrial design work. You must imagine the thing 50 years ago, it must have been kind of fancy to have one, as it is today. It is not as easy to service as the Mk2, but you can work on it reasonably well still. They do need a bit of service, all of them now. Mostly the back off pot meters are dirty. Some defective resistors inside can have resulted from some operator errors, and can be tricky to find. Like you can burn a grid resistor, and then the whole grid voltage ladder can't be calibrated any more. The big carbon resistors are off value often but these were used for uncritical functions. All other resistors are precision types, like 2%. Sometimes a diode can get broken, but that is easy to find.

It must be said, when a MK4 is well restored, it will last a lot longer again an the quality of all parts inside is still good today.

Some advice for buyers:

Unlike most testers, electronics inside work logical. Though not self explaining, and you do need a lot of experience. Also it is very full and compact inside, and you can not conveniently open it up. I am trying to tell you here, you better pay more for a GUARANTEED GOOD one, than pay less for the usual ones with the vague promises only. Damaged or sticky meter. Check for leakage with a potentiometer that you connect to the pins of a tube socket. You must be able to measure exactly it's values with the AVO. If this reproduces, that means a lot for a good meter, and for the tester also. If not, let go of this tester. Meters of those can NOT be found. Linearity can be terrible, and meter inside damaged by short circuited tubes or stupid operators. They're very sensitive meters, not made any more and CT160's are often slaughtered to get the meter out for repairing AVO MK4 meters. Then the bad Mk4 meter gets put into the CT160. All thumb wheels must run smooth, and printing must be clear. A non-smooth thumb wheel is very difficult to get it ok again. Some oil helps not much, and resolves the lettering paint. Voltages: Take a multi meter and check each and every voltage. Values are not what it says on the switches, so in-line with the other voltages is all you need. Only for the heater, the voltage must be as on the switches. Set the mains test mark, and then you need exactly 6.3V with a 6L6 INSERTED. Precision of the plate current test should be better than 10%, to justify maximum prices. You need a calibration tube of type 6L6 for this, with tube curves, to verify the tester at various points. Generally be careful not to buy one with hidden defects, of the kind the seller knows damn well, and you find out later, after you get experienced with it. Precision of 20% I would say it is normal. Below 30% don't buy it. A very used case, doesn't mean anything at all. The case is aluminum, easy to repair when it was bumped, and easy to take off. So what should impress you is PRECISION. Not shiny paint. OPEN IT UP before buying. Just four screws. Now check very very carefully for traces of repair. If so, that rather indicates an existing problem, than a fixed problem.

Goto to the AVO Mk4 main page

CONCLUSION: The BEST of all AVOs. FIVE STARS *****




Ebay prices seen:

2007: Very good one. 1675$
2007: Probably good. 600€
2006: Meter missing 200€

AVO CT160

This is the most unusual, and one of the finest testers I know. This tester works by a Wheatstone bridge principle. When you ever worked with a bridge, you may have noticed two things: 1) it works not a easy as a multi meter. 2) They are awfully precise. The reason for the precision is, the panel instrument is only needed to "zero" the bridge, and the actual precision and linearity of the panel meter becomes irrelevant. Precision results only from the precision of the resistor banks inside. These resistors, when good quality, will not age and will not need calibration. Same with this AVO CT160. You have to zero the meter by using the set knobs, and once that is done, you can read the plate current from the set knobs. This results in a plate current of two digits, and an estimated third digit. So you can read for instance 97.2mA plate current. The interesting part is, the third digit (here the .2mA) occupies a length of 1cm on the analog knob. So you can very easily estimate the difference between 97.2 and 97.4mA. On a normal 100mA panel meter you will never be able to do so, as the difference between 97 and 98mA is one stripe of 0.7mm wide. (vs 10mm with the CT160). Even so, the panel meter has 1.5 % error, whereas any error of the CT160 panel meter is irrelevant.

Once you get used to the bridge, you will do a measurement quicker as with the Mk4, as the nasty backing off is not needed. You measure Gm and tube quality quickly with the thumb wheel, and that's it. So the CT160 works faster, and is more precise. It's just not "main stream" and it will never be.

  • Advantages: Lower weight, higher precision and lower cost as Mk4. Less parts, so less can get broken. All critical parts put together on the side board. Just test them on this board one by one, and likely the tester is ok then. When you close the lid, the tester is closed dust proof, by a rubber seal, so the whole tester is usually well preserved.
  • Disadvantages: Unusual operation. Grid voltage limited at -40V. (Though you can add -40...-80V option yourself easily). It has no "shorts" test.
  • Typical defects when you buy a CT160 on Ebay: Grid pot wire interrupted. This is a very special pot, replacements are absolutely unavailable. I may be able to repair the pot for you. Better not try it yourself. Meter sticky, or needle damaged by shorted tubes, or foolish operation. When the meter is still moving I can usually repair it. Replacement meters can be ordered via our company.

. For a detailed test report, click here

CONCLUSION: Amongst the top-ten testers. FIVE STARS *****




modern appearance

 


limited nr of sockets

 

AVO VCM163

This tester is a strange one. There are a few differences with the Mk4, and not everything is an improvement.

  • The transconductance is not done via the backing off circuit as with MK4, which is an improvement. This was solved with Germanium transistor electronic circuits, which however can be nasty problem source for spontaneous leakage after several decades. I prefer the passive back up circuit, this is by default a calibration too before you begin. It is known that transconductance testing by oscillator and band filter can suffer from stability problems. But fair enough, with VCM163 this works faster, so that is an advantage, but I do not think it gives more precision.
  • Heater voltage is selected with a three digit number. Whereas with MK4, you have a classical rotary switch
  • Many of the vintage sockets are missing, in an attempt to be modern. Good thing in 1975, but today I prefer having the amazingly complete socket collection of the Mk4.
  • The grid voltage setting of the Mk4 is more precise and far superior. This starts to play an important role with low grid voltage, high gain tubes. For instance 12AX7. First Mk4 is divided in more ranges, and second the very beautiful gear system of the Mk4 is missing. In fact, the not so preferred, cheaper system of the Mk3 was used for the VCM163. Very strange design decision. Perhaps looking for "ease of use" but it was on the cost of precision.
  • Mk4 has anode links, and 2.5 mm plugs in the deck, for all tube electrodes. VCM163 has only the anode links.
  • Last but not least, the unique ultra sensitive leakage test of the Mk4 is missing here as well, and the lower sensitivity of the Mk3 is used here. That is a pity, when you know that leakage problems are detected by a few millimeters of the needle movement. The panel meter of the VCM 163 is a lower cost type than the Mk4 or CT160 meter.
  • The right meter of the VCM 163 replaces the gear-dial wheel of the MK4.

CONCLUSION: Less ideal and less perfect as many think, but still a very fine tester. FOUR STARS ****



Bias King

This is a nice little tool, being able to measure the plate current of a tube inside the amplifier. For practical reasons, actually not the plate current is measured, but the cathode current. So this means all grid current(s) are added to the reading.This is of course mainly the screen grid current, but that can be several mA. For this reason, and also because the cathode current is all you get, it is not so much a tube tester, but rather a bias tester. So the bias current is what you get. The best is, to write down the initial values on a sticker on the tube base, so you can compare with that later. Some small loss of plate current during tube life is normal, and with the Bias King you can watch this process, and see if the tubes are still in balance. Manual here

CONCLUSION: Better as you expect! Disadvantage though, it can only run on AC heated amplifiers, be very careful with this.



CANOR

The Alladdin Mk2 is a new made digital Tester from Slowakia. More information will follow.

DETAILED TEST REPORT + COMPARE WITH OTHER DIGITAL TESTERS



Centrad 752

I will describe it later. This tester looks a bit like a Taylor 45C. It has one defective selector switch that us easy to repair... just to have time. So I can not select any tube, but almost any. This little pearl is based on the circuitry of the 45C, but it has more and better options, also it had the selectors for any random tube, same as the AVO's have. All together this is a mix of AVO Mk1, Taylor 45C, and the designer saved absolutely not on nice options. It has for instance the professional leakage test method, same as the AVO's have. This means a real ohms measurement, but with a high voltage as bias. Thus the designers were aware, sometimes the one, sometimes the other method is better. Heater voltage very interestingly done, with a coarse and a fine adjustment. Well, I have not really looked at it in detail. Some incandescent lamps are used as a fuse, same as Hickok does.Fact is, the tester works, and is precise. It can do many of the European B4B5 socket tubes like PX4, PX 25, etc. Easy to handle and a nice design. It is larger as it looks on the picture, and quite heavy. Manual_French . Manual_Dutch . Meter_picture . Large_Picture_of_Tester



Ebay prices seen:
2007: 280$

CONAR

Almost unknown brand tube checker. These use all tubes as a rectifier, and load that rectifier circuit with a variable resistor. It's the "D" knob here. Work at too low voltage, and do more things wrong as well. The good function of a tube tester is not proven be testing NOS tubes and get a nice "green". The question is, if a particular "?" tube comes out just that way. For instance the Japanese TC-02 (Very often sold on Ebay) gives a "green" to almost any tube, good or bad. The TC-02 is a piece of junk so to say. However I had two TV10 from Superior instruments, looking the same way and these picked out the bad ones quite good. So yes, such a tester can work, but only if you have proof. I would say it is worth 50$ for the fun of owning it, but you can not test tubes with it in a reliable way. No stop! It's worth a lot more, because you can sell in on Ebay nicely. Yes, that's what you should do with it.

Picture series here

ONE STAR *



DIY Tube tester (1)

Many DIY testers exist, and it is interesting to see sometimes 50 years old versions of those. Some are really nice done, and some not so nice. Today, often the testers are made as digital products, and you can see the maker getting deeply into software issues, and the hardware getting larger as intended. For that reason, a nice way is use digital panel meters, and for the rest set up the tester in the good old analog way. From my own experience I can say, use only industrial meters for this. The Chinese Ebay meters have unlinearity problems. Suppose you calibrate it for 1000V full scale , and measure 99V. So you switch to the 100V range to get more accuracy, but you measure suddenly 98V. (Mmmm ?!) The reason is panel meter internal unlinearity. You can't calibrate that away. The expensive meters don't have this problem. Since the tester is an instrument, you need to make the full concept before you start, keep the wiring simple, yet prevent to forget functions that you have to add later. So the thing gets serviceable later. With the concept being "final" from the beginning, you can make a nice front plate, use nice knobs, and paint it professional. Here is one of those products, which I think is extremely well done. It was made by a private person. He is 78 years old, (while I write this in 2011). He admires tubes for the industrial design "art" in them. So this is somebody with time and experience, and the right heart beat to build something ultimate. The result is the most beautiful analog tester I ever saw. Read more about it.

FIVE STARS *****






Ebay Au ct. Nr 180693063337
2011: 699€
Picture here

Funke Einheitstester (W16 variation Model)

The is the first model of the one-knob testers which works without internal battery, and the negative grid voltage was made by the power supply itself. After this was made the W16, W18 and W19 which basically work the same, only have more sockets. This tester has received the name "Einheitstester" in English "standard tester" because it had only the European Standard sockets.

Click this link for a restoration project with this tester, schematics, and details about it's function. Read more...

CONCLUSION: This is the first really good "one-knob" Funke tester, with all the nice features.





Funke W19. Factory price in 1968: 425 Euro. 20 years manufactured, from 1952....1972.

This tester was made by a German Engineer, Max Funke who more or less spend his entire carrier building tube testers, and some other test equipment. This ended in two top models, the W19S and W20. He had a new model in preparation, but that one never made it into production, since the end of the tubes production was near. The W19 (S) is the largest and final model which is completely programmed via the punch cards. The W19S version is preferred over the W19 , since it has more sockets, a more useful case. A total of 5000pcs W19 were made, and I think most of them still exist because it's an after war model.

This Funke W19 made in 1968 , I bought on Ebay in said to be "working condition",  but that was just about it, for the rest it was a mess. At least the basic material was very good. The man paid me back some of the money, and for me it was ok then. I love good instruments, and I spend over one week restoring and calibrating it, including the meter linearity.  Now it is like new again.  The best about the W19 is,  is has no settings.  So you plug in the pins on the test card, and you can read if the tube is good or not.  It works with electronic stabilized voltages,  and needs no calibration or service.  When the control lamp burns,  it means the internal electronics is working.  They thought of the user's comfort.  I would say it's  THE tester amongst professional tube dealers.  It gives very reliable results. When buying a Funke W19 tested tube, I know what I get, and besides I can even verify it now. It can measure almost any tube, USA and American, and can be operated without having to think a lot, and the reading is stabile very quickly. So you don't need to heat up the tubes very long. (Though you do need to heat up the tester for 10 minutes, so the internal voltage stabilizer reaches it's accurate voltage). It is ideal for having to test 100's of  tubes.  When I verified the results,  bad tubes, were really bad, and "?" tubes are indeed just like that, and new tubes from Electro Harmonics, Sovtek, etc., are always indicated at or above 100%

Here is how the W19 works, it is as simple as efficient and reliable. The W19 works with test cards, and you can make no mistake with those. We all know this strange feeling when plugging in a 500€ tube in a tester. You check all settings 5 times, and still are afraid for your expensive tube to blow up. When testing an ECC803S with any other tester than the W19, first I plug in a cheap JJ tube. However when testing an expensive NOS RE134, I have no cheap JJ tube to try it first. Here is where the W19S comes in, it's a good feeling you can do really nothing wrong. All voltages are set by the card. The internal voltages are taken from a ladder network. So the plate voltage is stabilized, but also other stabilized voltages derived from this. Now what is nice, you rotate the only button it has, all though the positions 1...13. In position "0" the whole tester is off. From 1...10 it performs all the leakage and short circuit tests, and each test is passed when the meter stays on the "zero" position. Suppose it fails one test, the meter goes to the left, into a small white zone first, which is acceptable, and if it goes further a red zone begins, which is where "leakage" starts. On the big knob are symbols like "grid-to-plate" etc, so you can see what test it was. That is all there is to say about how it works. I tested it with a KT88 and an external 400k resistor from grid to filament, and it indicates the middle of the red scale. Perfect!

Position 11 is the actual test, and the results is pre-printed on the test card.

Position 12 gives the transconductance by changing the grid voltage from 0V to -2V. So you need to calculate the micromhos (=mA/V). The transconductance test is invalid with tubes that cut off at -2V, but also here the cut-off should take place, so at least that you know, and the tube is probably good. With other tubes you can calculate the transconductance like this.

Position 13 gives the vacuum condition, and you're done.

The cards are the software, the W19 the hardware. What is nice about the cards, they have the tube main data printed on them, including connections, and standard settings. Also many replacement types. Then it gives the actually test settings in the W19, the plate current, and most important, it tells you what is bad, "?" and good. These cards are really accurate. That's why I like the W19 so much.

Prices: I collect some from Ebay, prices are rising quickly. Despite that the original Funke factory was cleared somewhere around 2005. From that closure a lot of material came on Ebay, specially stacks of NOS test cards, several blue books, switches and meters. Even new cases have popped up on Ebay. Still prices go up and up. I bought mine for a few hundred Euro. You can only dream of that now.

There is the W19S and W19. The "S" is the military one, and looks less nice, but it has more sockets and a higher rated transformer. It can do filament current up to 4 Amps and plate dissipation up to 50Watt, but also can delicately and precisely measure battery tubes at less than a mA. It can test bigger tubes also with an AC plate voltage, which makes it possible to test any tube up to 250mA. The reading is in equivalent DC milliamps, which seems to represent real DC measurements nicely. I tried that out. Rectifiers can be tested used up to 250mA.

Making tests cards is a piece of cake, because when you remove the card, you have all the settings nicely printed underneath. So you can select the plate voltages AC or DC by plug in the correspondent pin. When the test does what you want, you can make your own card quickly from a sheet of paper, and stick the test pins through the paper.

WARNING: A Quantity of original factory carton packed W19 have been removed illegally from the old Funke warehouse in Germany, when the building was for sale, after the widow of Max Funke died. The seller of the building was a broker, selling it for the inheritants, and they had little idea what that "old stuff" was, and only interested to sell the building. Some insiders had keys, knowing damn well what this was. It was the complete inventory of a 45 years old running company. I was send pictures of this even, by someone who was in good and honest contact with the Funke family, and he was so upset by what happened. Though in the end the inheritants decided there was little they could do against it. They just wanted to get rid of the building anyway. It was a massive amount of half finished materials, incl 50 (!) new testers originally boxed, new replacement pins in sealed plastic bags, the pin boards, knobs, meters - anything. A complete wall with shelves, and a pile of each PAGE of the blue book. I saw pictures of that shelve wall myself. Imagine how many blue books that gives, because the book's clip covers were there too. Full boxes of resistors, sockets, TONS of new test cards, and may many other things. Like Ali Baba's treasury cave. All of it laying nicely sorted on shelves. It happened around 2006. TAKE CARE: By German law, you can not become the legal owner of stolen goods. And yes, these show up at a famous auction site sometimes. Also at some HAM markets I saw people there with remarkable amounts of NOS replacement parts.

Read more about the W19

Read here about an interesting 1935 patent from Funke. This tester was never made.


Picture from the patent

CONCLUSION: Top Model, no compromise tester. Ideal for for who want to get a very quick and reliable result, which is totally respected by everyone. I have one seen a W19 on Ebay, which was a very late model, and it had a semiconductor rectifier inside, and a ceramic multi-deck switch instead of the older type rotational switch. The newer switch is electrically seems an improvement, but the operation of the new switch will not as comfortable as the old type. The old switch is fine too, but it definitely wears out quickly. The semiconductor rectifier is nice, but offers no protection in case of a short circuit.

Ebay
prices seen:
Auction Nr:
2012
Good 1199€
221000641898
2012
NOS in box 2000€
251003864081
2007
NOS in box 1496€
290178443397
2007
Defective
450€
 
2007
good: 875€
 
2007
NOS in box 1375€
 
2007
good: 935€
330184793844
 
2006
Blue book: 40€
 
2006
Incomplete 200€
 
     
     


 

Grundig Tubatest

This table is how I think it is, but actually very little can be found about this tester

Tubatest: Version with connector at the back for the adapter kit
Tubatest 2: Version with the adapter kit build in, in one bigger case. The adapter kit has a switch for various octal based tubes. Also it has enough place to add Noval Sockets if you want.
Tubatest L3: A stripped down Tubatest (1), without the connector for the adapter kit

 

Interesting tester. Made right after WW2, under the company name RVF (Radio-Vertrieb Fürth). Tubatest can be found at low cost still, and it works nice. The Tubatest 2 that I have, is a nice piece of hardware, in a strong and nice case, and you can work on it easily. The switches are nice made and high quality. The way the operate is logical and well thought of. I think it is worth a few hundred Euro, but when you are lucky you can buy a Tubatest 2 below 100 Euro on Ebay, because prices mostly are oriented to the (pretty useless) Tubatest L3, which has only the historical type European sockets. So, Tubatest 2 is my secret tip, or otherwise Tubatest (1) when you can get it together with the rare adapter kit .

So, most information and price orientation in the internet is for the pretty useless Tubatest L3, but this had no adapter kit build in, and no connector for it either!

Link to Grundig official nostalgia page. The company still exists. On the left side of this linked page, you can click their products, and you can see they made beautiful industry designs. Around the mid 90's, they changed to making products with futuristic looks, of the kind that Chinese designers make today. So you see they were way ahead of their time.



HELIOWATT, Berlin Germany.

Technically very beautiful. Seems like a small Neuberger RPG 370. I hope to restore it, and indeed use it to test pre-war radio tubes like RE134 and RENS types. Read more about it here.

 

 

 



How to choose a Hickok Tester

1. Models before the Hickok patent. Very old testers, not practical today.

2. Technician models, Large case

Gives a quick result, easy to operate. Has some special features like life-time test. Medium precision. Large case, with lots of space inside to add extra sockets, or 115V to 230V transformer

3. Technician models, Small case

Simplified versions of the large case testers. Low precision, small size, low weight.

4. Laboratory models

Require more settings, but can also do more. Have higher generic precision, due to less compromises with the circuitry. Some have even a separate filament transformer.

5. Card matic

Link to: Hickok known issues, problems and general information

Link to: official Hickok company photo archive



General features of all Hickok testers

  • Micromho (=ma/V) readings, by means of a patented Hickok two-tube circuit which you will find in all testers with some variations. Some of the later solid state testers had the same circuit. Because of this "standard" circuit, each tester is a good one.
  • Future Tube life indication. The "English" reading with most of the testers. Some Laboratory models have additional tests.
  • Case is rugged and large, leaving us today plenty of room for upgrades
  • Wooden case is extremely rugged. Deck plate is nicely engraved and solid.
  • Gas Test. This is done with a standard test circuit, by putting a very high series resistor in the grid. The idea is, that tube gas gives grid current, and this will generate a small voltage over this resistor. The small voltage will add to the DC bias voltage, and change the bias of the tube. This change has always it's limits no matter what causes it. So regardless if it is gas if leakage, we always call it "gas" when you have a Hickok.
  • Noise test. This seem a nice method, though I must admit never tried it. You have to connect am AM radio receiver antenna to the noise test output, and if there is any noise, this will give loud crack sounds on the radio.

Not a feature of all Hickok testers:

  • Electrical safety. The non-grounded deck plate is DANGEROUS.
  • Show plate current.
  • Test at standard conditions for a specific tube
  • Test dual tubes with just the flip of one switch.


Micromho test

Let me tell you what that is. Somebody invented the unit "Mho" as a reverse value of "Ohm". That by itself makes me feel funny about it. In Europe they didn't want the word Mho, so called it Siemens. The ridiculous thing is now that we can call a resistor of 10 Ohms also 0.1Mho or 0.1 Siemens. The idea was to describe the conductivity (conductivity is the opposite of resistance) But actually all passive components have only resistance in my healthy opinion.

Now tubes are active components. The output current is regulated by the input voltage. So these try to conduct. Their behavior is best written down as milliampere per Volt. So you change the grid voltage 1Volt, and the output current changes 5mA, and we say the tube has 5mA per Volt. (5 mA/V). Here we go.... that equals 5000 micromho. Because Ohm is Volt / Ampere, and Mho = 1/ Ohm. What a useless mess!

Anyway this can not be changed any more, same as some countries will use miles and gallons, no matter how unlogical it. You must see the use of micromho in that light. Anyway, this explains why USA testers have micromho on it, and many USA data sheets too, whereas European testers always use mA/V.

To make it a bit more confusing, generally but not always, the micromhos are called transconductance and abbreviated as "Gm" and the mA/V are called "S" for Siemens.

English test

This is another of those things. English test is used by the Hickok testers, and it is a not so good way trying to say you are testing the tube under (an unspecified) load condition. The AVO company in the UK probably made the best recognized series of testers, that tested the tube under load, however they specify exactly what load, and you could read that on the meter, and make all settings yourself.. So you could compare that with tube curves and data sheets. Apart from that, they invented this red-green scale, where the good/bad result is derived from the transconductance (data sheet !) values. So very clever, and very straight forward. In the USA that was called "English" testing.

This AVO method was patented, which was a major strike. So Hickok had to patent something else. They patented the "English" test method, which is the RED-GREEN scale you see on most of their testers. I investigated the test results of know to be good and know to be bad tubes, and my conclusion is, it just derives a good/bad value from the already know Gm value. Same principle as AVO, but they (have to) do it in another way, in a very strange way, and in the end the RESULT is the same as with AVO.

Test results: With a socket adapter, I just measured the plate current of the tube, while turning the "ENGLISH" dial, and guess what.... Nothing changes! Only the needle moves when you turn the English dial.

So I can only conclude, this changes the sensitivity of the red-green meter, and nothing else.

Still the English test is the most used, since it tells you "good or bad", and the setting of the English pot meter from the roll chart, is the knowledge of the old tube exerts, put into the tester. Admitted is, the results are very reliable, that's why I keep my Hickoks, no matter what. Some testers like TV7 have only the English test.



49-A

Will upload pictures later. This is an older kind of tester, probably already having the Hickok patent inside.



For Calibration, multi meter.

This old multi meter is worth mentioning it here. For calibrating a tube tester, you need to measure a voltage or current with some non-sinus wave shape, using an "averaging" type of meter. Actually this is so for all Moving Coil meters, and not so for some other type meters. Next, you need a 20.000 Ohms per Volt meter, as that was kind of normal in those days, and the voltages measured take into account the load of the multi meter So with a digital meter, you make some errors. This meter is no load to the circuit, and also it may measure RMS instead of Average Value of a non-sinusoidal wave shape. Actually you can still buy new analog multi meters today of 20k ohms per Volt, there is some "Retro" thinking with many people, just trust a good old analog meter, that has no empty battery when you want to use it, since is has no battery. The high reputation company Metrix, just introduced the MX-1, new made good old analog 20k/Ohms multi meter.

This meter I found for 7 Euro, and it is great. It is by the East German (DDR) company EAW. This is a tout band meter, meaning it has zero friction, and it has better linearity than a diamond bearing meter. A tout band meter is very exclusive for a multi meter. It has the required 20k Ohms per Volt, that we need. Also nice, it works up to 3000...8000 Hz depending on the range. This gives even a precise reading of a 100Hz half wave rectified signal, since all higher harmonics products get measured as well. So you feel perhaps you now, this meter is going to do what you want, if measuring a strange wave shape, such as in the Hickoks or AVO. Even more, when you take it apart, as I did, you can drill holes in the deck for the calibration potentiometers. (Finally an analog multi meter I can calibrate, I never saw that before) It already has those potmeters inside, one for a AC and one for DC. This is really a goody. Then, It is class 1.5% on DC and AC! I checked it vs. a precision meter, and it has the 1.5% indeed. After calibration is it so amazingly precise, and definitely something I can calibrate a tube tester with. Search German EBAY (ebay.de) for: "Bakelite multi meter" or "DDR multi meter" you always find a few. People don't know what this is, and think it is old junk. Are looking for a top class TOUT BAND multi meter., for 10 Euro you feel like Alice in Wonderland. Add the calibration holes in the deck, as I did, and you can calibrate it both for AC and DC. I think you have a hard time finding something better. Besides in can test both voltage and current at the same time. Very nice. Well I hope this doesn't make the prices rise, but there are many of these around, don't over bid! Sometimes there are five per day at Ebay.de, sometimes none.



Hickok 531 (technician model, large case)

This is the same as the I-177, only the 531 is the civil model. It doesn't have the potted transformer, and anti fungus treating of the I-177. It is a very old one, so before you buy it make sure it's not rusty inside. It is a nice tester though when you have a good one, though the general rule applies here, if the case looks rotten, the inside is also. The mains voltage meter you see with this one, is retro fitted. The standard way to adjust the mains is via the main meter.

CONCLUSION: Better buy am I-177 TWO STARS *****

 



Hickok I-177

Tester settings for all tubes

 

Ebay prices

2007: Very good one. 200$
2007: Seems ok. 150$
2007: Broken. 75$

Hickok I-177

This was my first tube tester. I have two of those. I bought the first one in 1988 for 45 guilders (20 Euro) in the same old electronics shop, where I bought my stuff when I was a kid. He had them piled up. (Radio Kwakkelstein in Vlaardingen). Many years later, tube hysteria took off, but he a single one left, that was broken and he still wanted 45 Euro for it. I took it for spare parts, but never needed any. The thing was made to last for ever, and work without maintenance in the humid and warm countries where the US army was saving the world from communism. So even if you find a stinky old one, it might be good still. It tests all tubes from before the Noval tubes. For later tubes there is an adapter kit, which by itself is a valuable item, since it is a universal socket adapter for any tube tester, not just I-177 and not just Hickok. The I-177 is a really fantastic tester, because it gives remarkably reliable results on the good/bad scale. What is also great, it has only two knobs to choose tubes. Instead of nine (!) with the later models. They all need a calibration badly, if never done before. If this tester says the tube is "just ok" you can bet it that is just what it is. Most of all you get used to the reading when you test the same kind of tubes, and if you see a tube which is into as good as the other, you better throw that tube away. ( or sell it on Ebay (ahem....)

Basically this is THE Hickok tester for the pre-noval tubes. The later model was the TV7 , which could do also test Noval tubes.

The I-177 has an interesting way it operates, and this is worth a few lines here. They use their famous patented Hickok circuit, but in the I-177 they added a potentiometer which does noting else then change the meter sensitivity. The signal going to the meter has to pass an attenuator potentiometer. This is the "L" potentiometer. The result of that is, you can test any tube at all, and have a correct reading on the good/bad scale when you know the setting of that attenuator potentiometer. (Of course they knew that at Hickok, and this is the "L" value in the handbook). Since the good/bad readings are done by measuring true, dynamic Gm, there is also this particular position of that potentiometer where the Gm (micro mho) scale is valid. This position is marked with "gm" on the L Pot scale. So the good/bad reading and micro mho reading is done with the same circuit.

Their patented Gm measuring circuit is the best of it's kind as far as I know. Due to this patent all other manufacturers had to work without it.

It tests all known rectifiers. Also the big triodes like 300B can be tested, and as we know there are not many tube testers that can handle this tube. Not even all later model Hickoks can do a 300B. By experimenting with the settings I can now measure many unlisted tubes with it, like C3g and EM34. It's really a very nice tester, very much recommended. The circuit diagram is inside the tester on a plastic plate. (Fungus proof....), and an Excel list with all test data I found in the internet. These will all work in 100 years from now. They used to be cheap, and regardless useless. Some start to understand how good they are, and prices of those went up a lot over the last years. The bargain days are over, a good tube tester is expensive no matter what. I think these are still a good buy for the money.

Here is how to find out settings for an large size tube, like KT88 or so.

  1. Find a tube with similar pin out. (that always exists)
  2. Set the L pot to the middle position and Gm Sensitivity to 15.000
  3. Set the Bias (R) pot for highest reading. Now rotate R clockwise, until you read 90% of maximum, and this is the bias setting. May be take a little less when the fuse lamps indicates a lot of current, and you think this is too much. The calibration comes in the next step.
  4. Find the right Gm Sensitivity knob setting, so that the meter is nicely in the green. (somewhere)
  5. Adjust the L pot until the tube is in the position of the good / bad scale where it belongs. So that is just in the green for a fairly used, "just ok" tube.
  6. Now L + R + Sensitivity is a set of information that you must use in that combination. This is a relatively high bias, which is hardest for the tube. I verified some Hickok settings, this is how they seem to do it.
  7. And that's it.
  8. Here is the KT88 setting I found that way.

A=8 B=5 Fil=6.3 L=70 R=42, Socket E, Gm switch at 6000.

I have not yet tried this for small tubes, like ECC83, but there was no need also. The manual was complete so far.

CONCLUSION: The best of this tester is the good/bad test. It discovers any potentially weak tube. Good buy when you use pre-war tubes. It can give the real Gm value of the tubes, and good/bad indication. It has no sockets for modern tubes. Use the MX949 adapter kit, and you can test any modern tube also. Make sure when you buy the adapter kit, you have the extended manual with it, otherwise you only have the adapter kit, but not the settings for it. They are all extremely out of calibration, so that needs to be done for 100% sure, unless the seller did it already for you. (I am sorry, we do not offer calibration service). THREE STARS *****



533A, 533B (technician model, large case)

The A-Version uses only a 2.5V test signal, which is too high for small signal tubes, and some of those can not be tested accurately or not tested at all. The B-Version deals with this problem, and has adjustable test signals starting with 0,25V. Tubes that need lower input signal, are tested with lower signal. The ranges are switched automatically when you change through the Gm scales. So 533B is much preferred over 533A, if you also want to test the later kind of tubes.

Picture series about 533B here



534A, 534B (technician model, large case)

The 534 is a 533 with a build-in multi meter. For all other information, refer to the 533, also for the issue with the test signal voltage. (So 534B is much preferred over 543A )

More information here



 

TV7 (technician model, small case)

This one came after the I-177, reminds me a bit of the 600. It has very few sockets. No direct reading of Gm in micromho. It has very straight forward way of operating it. What is nice, is the test switch and the short-circuit switch are combined, so you go automatically through the short test, before doing functional testing. Very popular tester. Switches inside are ceramic. Very good service documentation exists still today, and it has nicely arranged calibration settings inside. So if you only want to do a good/bad test without knowing what or why, this is your tester.

CONCLUSION: Disadvantage: High market price, low functionality. Advantage: Compact reliable, easy to access internal circuit .THREE STARS ***

Ebay
Prices Seen
Auction Nr
2010
NOS
660€


600 (technician model, small case)

This is a simplified version of the 5xx series. They left away some test options like lifetime test. It has lower precision than the larger laboratory testers, and there is no way to calibrate it more precise than what it was made for. Reason is, the Gm reading is done with a particular setting of the English scale. For instance for the 3000mmho scale, you must set the English pot to the red dot "3000". Then read on the 3000mmho scale. So this saves the range switch, the 5xx series has. The 600 has a red dot painted on the English scale for each range. However, the 3000 dot is almost at the beginning of the scale, may be only 10...15 wire windings away from it. When you try to set it precise, you will notice each winding of the wire wound the pot meter will give a change of the meter indication. So no matter how small the dot is, at the beginning or at the end of the dot, you have two different readings. Needless to say, the position of that dot is hypercritical. It means you depend on the original factory precision, and you have no practical way to make the tester any better than that. However the small size and simply way to operate it, made it very popular. It sort if did what the not-so-critical technician needed, and frankly speaking it still does so today.

FOUR STARS ****




Hickok 600A

600A (technician model, small case)

I do not know what the extra feature of the 600A is compared to the 600. The tester you see here, is my own but I sold it in 2011. The advantage of these smaller ones is their weight and size. The only practical disadvantage I see, is some smaller accuracy, but you have to know for yourself what accuracy is a "must" and what is a "want". Given the age and condition, a good 600A can measure within 10...15% which is more than you need for practical use.

Picture1 - Picture2 -Picture3 - Picture4 - Picture5 - Picture6

How to use it, with pictures. This is from my own 600A:

1) Set knobs by roll chart, insert tube
2) Press Line test, adjust
3) Read tube test result. Here for 12AT7 EHX new tube. This is a strong one.

605A (technician model, small case)

This is the same as the 600, only the 605A has a multi meter inside



539A, 539B, 539C (laboratory model)

The largest laboratory testers. For me, these all have one BIG disadvantage: the English scale is missing. So the tester doesn't tell you if the tube is good or bad. You're supposed to be able to tell this yourself. The so called advantage of the bias setting with it's own voltmeter is only a marketing gimmick, because the scale is too tiny, and unprecise.The the 539 series are easier to calibrate than the 750 series, but a well calibrated 750 is also something very nice.

Hickok 539A

Just purchased it from Mr. E. Dekker from Belgium. Will be described in detail later. This is how he offered it on Ebay:

"This tube tester is fully operational, all controls and roll chart work smoothly. The outside black Tolex covering does have nicks and tears but this can easily be recovered. All three meters are fully functional with smooth movement"

Actually this is the kind of description I can only advise you to look for. No uncles, no friends who tested it. The seller was the user himself, and he even pictured his tubes tested with this one. So I thought I was safe. Then when I received it I could not believe my eyes. The Tolex was fully torn away by some form of idiot. Here is what I received. Pic1 - Pic2 - Pic3

Next thing: "This tube tester is fully operational" Mr. E. Dekker from Belgium writes. Well, the Gm value reads twice the vale as it should be. So it is useless. He tells me this "must have happened in the mail". Interestingly, he points out already in the auction text to accept no loss of accuracy that happens in the mail. Now look at that... So he already "expected" the tester to damage in the mail. (You see what I mean?).

Now look at the Ebay picture. This tells it all, but I must admit I didn't notice while bidding. Here you see a tube tested, and the meter is all in the right corner. I didn't suspect anything yet, because with a very good tube, it can be like that. Only the problem is, it does so with ANY tube I try, even a broken one. Press the test button and the meter gives a minimum of 100% reading or more, no matter what tube, even without a tube.

Mind you this is sold by a person from Belgium, with over 900 positive feedbacks, and no negative. Well, this tester was broken as can be. I offered to give it back, and he writes: "No discussion possible". Don't understand me wrong, this is no way to complain about a bad deal here in EBAY. I put this here on the web site so you can all see what appears to be normal at the moment. Please learn from this, even people with all positive feedback do this.

So this is going to be my next restoration project. Then I will show here in detail if there were any other hidden defects in this tester, and what I had to do to repair it. For the readers of this web page, this was my learning experience, and it happened to me, though I really tried to prevent it.

Conclusion: This tester gives completely useless readings, the case was wrecked up by a monkey, and the main meter sticks.



Hickok 750

Both 750 I bought, had good basic substance as I got it. No serious damage, and only worked by good technicians. Well almost. One had a sticky roll chart, which must have driven the owner crazy, ending up using a big screw driver, violently pushing the wheel, until it all broke down. But that was all of the mistreatment it got, and I could fix that at almost no cost. I had an NOS roll chart, and digged up a new thumb wheel. It seems to me, the later roll charts are simply too big, and these roll not smooth for that reason. For making it an accurate tool for daily use, there was a lot to do still.

The other 750 I have appears virtually unused, but that doesn't keep the electronics from aging.

The 750 is a refurbished 532, and Hickok tried to replace the 539C by it. My opinion is, the 750 is one of the best Hickoks there is, and more useful than the over hyped 539C. More about this later.

What is really nice with the 750, is has additional to the classical two tube Gm test, an adjustable DC voltage of 200V, 100mA. I found both my 750's can not supply full current and full voltage simultaneously, so that must be how they are. When exchanging the 83 rectifier for an 83V, maximum currents exceeds even 100mA, while the micromho readings don't get affected. Perhaps I will change this later, but I think this is going to take some exchange of other components too. At least I need to check this better, and for the moment I will leave it as is. The voltage option lets you test stabilizer tubes, but you can do also other things with it, as you like. If you don't know how to do that, it's better only to test things as indicated on the roll chart. Later on, I will show you how to repeat Funke W19 tests with it.

The 750 differs from the smaller testes like 533 and 534 because it works with different AC test signals, instead of a fixed signal. It has this in common with the 539C. This allows testing of tubes with very high gain, so no overdrive will occur. This makes a 30.000 micromho scale possible.

They put back in the load test in the 750, which the 539C is missing. I think it was a mistake, to remove that with the 539C. The latter can only measure transconductance, no load test is done. Also you can't compare the transconductance you measure with the 539C with your tube book, because the plate voltage of the 539C is too low, and simply wrong for most tubes. Next is, the roll chart data of the 539C is lower than for a new tube. That was done to give you a way to pick out the bad tubes, because in the end that's what people want. So Hickok put a non-standard roll chart in the 539C, with lower values than normal. So they printed the reject value on the 539C roll chart, not the "new tube" value. (of course you 539C users, you all know that... he he). This makes I don't like the 539 so much. To to stop the confusion, Hickok put back in the load test in the 750, and also give standard tube data on the 750 roll chart, same as with older (normal) testers. That was a good decision.

I never found any documentation about how this load (English) test is really done. The word "English" suggest the AVO method, like in the Mk2...4, and CT160. I will check that later, with an oscilloscope. The oldest tester I have, using the AVO so called "patented" method, is... a German military tester that I estimate from 1938. For the moment let's trust Hickoks experience, giving us the correct "English" dial setting for each tube. Somebody in Cleveland Ohio (where this tester was made..) must have had a huge cabinet full of good and bad tubes, and just tried out the right settings. The roll chart is the software of the tester, so to say.

( I know it was done like this from the book of Harvey "Gizmo" Rosenberg, who described the work of Julius Futterman. Before the war, Julius used to work for a company building tube testers, and tube manufacturers would send him all kind of tubes, to update the roll charts)

Now go to the restoration page of this tester. There were many things to do.... Please note the repairs are for both my 750's. So you may notice small differences in the pictures.

WHAT CAN BE DONE WITH THE 750 AND WHAT IS NOT IN THE MANUAL:

1) FUNKE W19 simulation. Here is something really new. With the 750 it is possible to do the Funke W19 tests with your Hickok 750. All you need is the famous Funke Blue book, which costs you about 30..50 Euro, and a copy of the card set which is on Ebay for 15 Euro. The Funke W19 is extremely popular in Europe, a top model, but it is completely ignored in the English speaking territories, except Asia who love the W19 also. Now don't ask me why that is, but this is where we are. The W19 is mainly an Emission tester, and the best and (only) one that deserves the name. Test results are undisputable. This tester proves what a good Emission Tester can look like. It is at the level of the better Hickoks, in terms or reliability, accuracy and correct test results. So if you have a Hickok 750 (or 539), read here is how to do Funke W19 tests on it!

2) Forward voltage of rectifier tubes. This is of particular use in the laboratory If you don't know much about tubes, and only want a quick result, you should use the classical test a by the roll chart.

Example: The 80 rectifier to my experience should have a forward voltage of 25..40 Volts at 60mA to be good. Where 25V rarely happens, and above 45 the "bad" range begins. Also note what it does at lower filament voltage. A good rectifier does not significantly change it's forward voltage if you do so. On the other hand, if the forward voltage is higher than normal, and you set the filament voltage one click higher, and the tube significantly improves by this, the tube is worn out. You can try to ge those results in-line with the classical test as on the roll chart. To do this test, just set up the tube from the roll chart first. Then set the "Adjustable Voltage" to zero, and the test know to position "H" for high. Flip the Vr-Mils switch to mils, and slowly increase the voltage until you see the milliamps go up. Check the forward voltage, this is when Vf begins. Then go on until you have 60mA and read the Vf now. Then do the other plate (switch setting is at the roll chart). You will see this is very easy to do, and you learn a lot about the tubes.

3) Forward voltage of Power Zener diodes. Same procedure as with tubes. Only you have to prepare an adapter this. Remove the base from an old octal tube, and connect two wires to plate and cathode. Take the connections for the VR105 tube. Make sure you don't reverse the Zener, and don't boost 100mA into a short circuited Zener, that is probably not so good for the tester. You will be surprised how bad solid state zeners actually are, they have high temperature drift, and bad load regulation compared to tubes like VR150 or VR105.

4) Continuity tester. This one is from the manual actually, but it's nice one. You can use the 750 as a continuity tester, when you set the "shorts" switch for position 4. Then put two probes in the "grid" and "plate" connections. Because the tester has an isolated chassis, this is of no danger. Then the neon lamp will burn, below 200K resistance. Nice for checking switches, connectors, etc.

FIVE STARS ****



HICKOCK. TV2. Military (laboratory model)

It can test all tubes under real conditions. It comes in the same category as German Neuberger RPG375 tester, though the last is card tester, not switch operated. TV2 is unpopular though, but I never had one here, so I can not say what is the reason. What is unattractive (for me) about a TV2 is following: It is a tube analyzer, not a tube tester. Now when you have an analyzer, you often want to connect a multi meter to it somewhere, like measure the filament current with a digital meter, or one of the voltages. It often comes down to that when I use the RPG375. So a voltage test point AND a removable current bridge on all tube connections. Particularly THIS is why I use an analyzer like U61B or RPG375.

Next thing is, you can set the plate voltage and grid voltage nicely by the data book, and then get a test result called "Percent Quality". Whatever that is supposed to be, that is not what to know. When I must set exactly plate voltage, and grid voltage, I am sorry, but then I want to see the plate voltage and Gm as a result, and additional some "Quality" indication in percent. Still for that I rather have the red-green scale if the 750A or 600A. Then I know what I have. So personally, I think this is what makes TV2 a strange thing.

It seems to me people don't know what it's worth, I have seen them go on Ebay in nice condition for 200$. Also see people ask 1800$ for it, which is definitely not what they are worth. When you are prepared to that much, you better buy a guaranteed to be mint condition Neuberger RPG375 or Metrix U61B, and enjoy that tester for the rest of your life. Working on Hickoks means they are easy to access inside, but the wire spaghetti makes you very tired. Actual failures are small, but hard to find. While working on a Neuberger RPG375 is a pleasure. All inside parts are nicely arranged in a row, on metal sub chassis, with clear cabling. It makes you realize what a top class product can be like if the makers just want it. You can repair a Neuberger RPG375 with an uncalibrated multi meter, and basic electronics knowledge. You can't say that from a Hickok. (However this does not apply for the older Neubergers, these are very hard to service as well. However the compare here is between the TV2 and the RPG375.



HICKOCK. MX-1258/U Tube Socket Adapter

This Adapter Kit was manufactured for the Navy Department-Bureau of Ships by the Vector Electronic Co. of Los Angeles, California. It consists of nine types of adapters, mounted within an aluminum transit case approximately 6" x 9" x 2 1/2" complete with handle. The adapters are secured within the case by means of mounting clips. An addition clip for securing the instruction book is provided in the case lid. Pin straighteners for the 7 and 9 pin miniature bases are permanently mounted in the center of the transit case.

The tube socket adapter kit is intended for use in general electronics testing on equipment employing electron tubes. The nine adapters contained in the kit provide the facility for testing circuit conditions with practically all of the commonly used electron tubes.




Click this picture!

 

Ebay prices seen:

2007: Good one 680€
2007: Defective 313€

ELPO 508

Bought it on Ebay, and got cheated with it (as always). According to the German seller it was very accurate, but it produced complete nonsense when I tried it. What's the use if a nice and friendly old man is prepared to take it back, and all the mess and work was for nothing. So I decided to keep it, and repair it later.

Well this tester is a strange one. It seems to me like an AVO Mark 5. The principle is completely the same as the later AVO's have, only compared to the ELPO 508, the AVO's are almost primitive construction.

Selector. It does have the nice AVO selector switch on the top, so company connections to this AVO clearly must exist. (Who can help me to find this out???).

Overload Relay: Who owns an AVO, will know the overload protection is very inaccurate, and a problem source too. Well this one has a nice, very sensitive electronic circuit, which does the same as that relay in the AVO. Nicely build on a printed circuit board, and it obviously replaces this relay. On overload it switches from a green scale light to a red one. Nicely done, looks like taken from the AVO CT160.

Sockets: These are the beautiful (and best I have ever seen) tube sockets as used in the Russian L3-3.

Circuit diagram: Partially hand drawn"blueprint" ( A real blue one).

Operation: I have an AVO Mk1, Mk2 and Mk4. When you are in the position to compare these, you will know these more or less work the same, only they get more mature, and higher models are the more convenient to use. (not give more precision, just more convenient). The Mk1 is for instance more precise then the Mk4, and Mk1 needs no calibration. Only, Mk1 is a bit strange thing to use. Interestingly, the ELPO works like the Mk4, but.... it is much more convenient. That is because it can do all a MK4 can, and has a much simpler way to archive this result, whit less knobs. Someone has done a very good job on this. So the way I can see it, this company ELPO actually took the Mk4, and improved it and make indeed something like the Mk5. It also has many more calibration points inside, from which I expect it will deal with some of the un precision the AVO MK4 has. I decided to restore it, and investigate this. This is why I kept it, and not send it back to the fraudulent seller.

QUESTION I have only the polish manual, which is very nice and complete, but I can't read a word. Who can tell me how to calibrate it?

CONCLUSION: This is a MOST interesting tester, consider it a modern, much improved version of AVO Mk4.



Link to manufacturer


Functions in English (click picture)

KALIBR. Model L3-3 from 1986

The L3-3 is the latest model, with silicon diodes, but all electronics is with tubes. The L3-2 is similar, but has still tube rectifiers inside. The L3-3 is is one of the most amazing testers I know. When I bought mine in 2002, the tube tester market was not so over hyped as it is now, and this tester was regarded unknown Russian stuff of little interest. Right now, things have changed. Understanding of this product has improved at least 25% over the last 15 years. (Yes, this means what you think it means:)

Who used old instruments, containing power electronics, will all know they need a repair sometimes. Something breaks here, something gets s defective there, and it just belongs to daily use of an old instruments. One L3-3 I have is NOS, means it was never used before. That is not always an advantage for old equipment, because often that means often all capacitors are bad. The other one was used very often, and it was officially calibrated every year until 1999, which was the last calibration sticker on it. The NOS one stabilized perfectly after 100 hours, and the used one worked perfect right out of the shipment box. All I had with mine, was a minor problem with a plastic cover from the inside detoriating. That I can replace easily by a wooden cover. My L3 never needed never any repairs at all. Only service, like a defective control lamp. All parts are still original, even the tubes. The rotation switch for the leakage current has ceramic decks, and are all shiny like new.

Handbook, detailed pictures, schematic, calibration, and a lot more... Click here to go to the L3-3 Page.

EBAY BUYING ADVISE: Unfortunately the supply of new, NOS, perfect quality, L3-3 is low now, which attracts fraudulent sellers at Ebay. The problem is with Eastern Europe, Ukraine, Slovenian, etc sellers. There are many defective L3-3 around. They sell simply those defective testers, with some stupid emergency repairs, screwed up meters, damaged transformers or burned parts inside. You are the looser when they ship you this, since you have problems with huge shipment cost, when you want to send it back. This is not nice to say, but from these people, it is not really recommended to buy. So you are generally better of, buying the tester from near-by. Also, it is much recommended to request a known tube, pictured in the test mode, so you can see the thing works. When they write not to be responsible for shipment problems, this is a trap, to send you a damaged tester. Don't buy it. Read here also. Not recommended sellers: hickoks, sunnygirl505

CONCLUSION: Amongst the top-ten testers. Best buy ever for the money. It gets a well-deserved:

FIVE STARS *****

Ebay
prices seen:
Auction Nr:
2012
NOS
no cards
605€
110981376833
2010
NOS
no cards
399€
2010
NOS
All complete
430€
2007
Incomplete
99€
2007
Defective
250€
2005
NOS 430€
(my tester)


KALIBR. Chinese Version

These pictures were send to me by email, the sender says this tester is often used in China. I have never seen this version. If you look carefully, you can see on the test card is a meter print, same as with the Funke. It has two mains transformers. From the different hardware and different switches on the deck, this seems a special model. but it can be easily recognized the factory is the same. It might have been a good idea to add this scale to the L3-3 cards.



Ebay prices seen:

2013: Good: 1300€
2006: Good: 900€
2006: Defective: 350€

Company website they seem to be hiding it. If somebody can find it, let me know, so I can link it here

 

METRIX-U61B / or U61 B

Somehow, this one does the same as the RPG375, but is deals with the negative points the RPG375 has. The Metrix U61B has no cards but many switches.  So it is more universal, and I find it quicker to use.  Also the internal voltages are electronically stabilized, so no readjusting of plate voltage when a tube draws more current. Also it has connections at the front plate for digital instruments.   Vacuum quality can be measured with tube testers like this very good.  For better measurements, this beautiful instrument  has a special connection to measure grid current directly, by connecting a nano-ampere meter to the tester. A great feature is the tube protector circuit. When the plate current meter is more than 25% above the maximum of the meter, the plate current will shut down, and you need to reset it. This is done with a very special, programmable current sensitive relay. So at each meter setting, it has another sensitivity. Another protection is when a tube has a short circuit, this will disconnect the whole tester from the mains, and a red indicator pin comes out of the front panel, that you need to press back in, to switch on the tester again. This is a master piece. I use it for the very expensive and delicate tubes, like ECC803S etc., because of the plate current protection circuit. Also well suited for testing large numbers of tubes, Because of the protection circuits. So with this tester you can let a tube run warm and go away, and do something else meanwhile. When the tube starts to draw too much current, while you don't see it, the tester will shut down with a loud "clack". It happens often with KT88. So you'll hear that and can check it.

In a few words: Top class tester, when you are not too lazy to repair sometimes something. I had a few small repairs with mine, just some small capacitors were bad. Very convenient, and very versatile to use. Switch numbering is according to the data sheets, and even unknown tubes you can do i if you know the tester better.

FIVE STARS *****

Read more about it.



Enlarge

Ebay prices

2005: untested 35€ (mine!)
2005 : Mint condition: 229€

Neuberger RPG237 from 1938

Front plate - Leakage-tests-buttons.

Lovely build tester, with high quality switches and precise meters. The Neuberger RPG 237 was a standard for it's time. It is an AC Tester, sweeping a tube through the WHOLE RANGE tube curves while testing it. So getting "20mA" as test result, means it sweeped the tube through the complete set of tube curves, at different plate voltages and different grid voltages, and it produced 20mA as an average value. Suppose you measure a tube that must give 20mA at normal settings. The RPG237 then gives a very good impression of the lifetime left in the tube, because if the tube can do the 20mA, but can NOT do the peak current any more, you will get a lower reading than 20mA, which is right!

This instrument is a genius. Plate voltage, screen grid and control grid can be separately set. With the differential of two measurements this allows to determine transconductance (mA/V), gain and Rp. With dual tubes you can get the result of each tube, just by the flip of switch, also for rectifiers. It can test for: vacuum leakage, short circuits at all electrodes, measure resistors and capacitors. Apart from tubes, it has some multi meter functions, also for testing capacitors. I tried a few Mundorf precision capacitors, and all I can say, it indicated the values exactly as printed on the capacitors. Wow!

It's not in the manual, but since it can measure e capacitance, I guess it should be able to measure grid capacitance as well. Just a matter of connecting everything the right way. 

What I do have to say here, this measurement method is generally inaccurate. Even the so called "top class" AVO's give nothing but a rough estimation. However.... not with this tester! Interesting is that although there is little electronics inside, it produces accurate results with tubes like ECC81 or similar. I had to connect those externally, because it has no sockets for those. When comparing the results on the L3-3, I can say this RPG237 still works fine. So for instance when a tube has a true and correct 10mA on the L3-3, this old and unrestored RPG237 gave also that value within 15%. Yes, really amazing! Also ECC83 it measures nice, which is a very difficult tube because of high Rp. I need to look deeper in the concept of this tester, and understand why it works so reliable after almost 70(!) years unserviced condition. 

In a few words: Still perfect fine after 70 years..... AMAZING. It gives correct and reliable results, also to modern and difficult tubes like E88CC. The disadvantage it has no modern sockets, but you can solve that easily by connecting a Hickok adapter kit MX949 to it, and you're done.

THREE STARS ***




Testing EF804S


Testing 211 tube

Ebay prices seen:

2005: Very good one: 850€
2007 Very good one: 1120€
2008. Very good one 1509€ (link)
2011. Very good one 2500€ (link)

 

 

 

Neuberger RPG375 from 1965

Their final model, and largest tube tester they ever made. The Neuberger company still exists. This is a parametric tester. Can measure vacuum, and show all parameters at the same time. Dynamic tests are made as difference of two measurements. I have this Neuberger 375 from the widow of the first owner, and it was said he never used it. The tester appeared fully unused indeed.

The meters are very good. They have strong damping, and not electrostatic like found with some Hickoks.

All voltages + currents  can be measured at the same time. Some meters have more functions.  Connections are on the front for external instruments, but the build-in instruments appear to be incredible precise, so you don't need any external instruments. This is no quick tester for radio shops or TV Repair men. This is a full featured laboratory instrument.  It is card-based, but no need for using cards. When you want you can do all settings by hand, and there are standard banana connectors to all tube pins, and also current links to each tube pin. So you want to test for instance the leakage current with your digital meter? No problem, take out the link, and put the meter in.

If you know how to do it, you can also tap the plate voltages and other voltages, use it as a multiple power supply for lab experiments, with all voltages and currents adjustable, and with meters. So you have a 500V 100mA power supply too, and connections are simply on the main plug-in board, top left. (see the picture I used). The plate voltage is tube rectified with Telefunken tubes. These give natural protection against short circuit. So a short circuit will not blow the fuse or the tube under test, but uses the rectifier tubes as the current limiter.

I would say, with this tester you can test almost any tube. I have tested the 211 with it, which is a high voltage tube, but the tube curves do go down to 500V, and at those points I tested some new 211, and the data from the curves reproduces very nice at this tester. (See pictures here)

Also the 6C33 can be tested when you use an extra socket, same method as with the 211 tube. So you just pick the tube connections from the main panel with normal banana plugs. So there is a (banana plug) connector for "plate", two for "filament" etc etc. As far as I know, there is no other tube tester that can supply the filament current for the 6C33.

It features the very nice Neuberger Rotational switch, before you test a tube, you can do leakage or shorts. This switch works the same as the Funke W19 or W20.

Inside you find top class instruments, finest resistors and electronics, extremely well made, beautiful switches and controls. It is the absolute winner in terms of perfect construction, no other product comes near. Note the deck has no German on English words, only symbols. So any country, you can use it.

In a few words: A top laboratory product, when you have the muscles to carry it. Disadvantage is the unstabilized voltages, and older type sockets are not available on this tester. However it is one of the few (or only?) vintage testers that can do adjustable 500V @ 100mA. It can test all tubes from tiny fragile to big and heavy. The card system makes it fully universal, and SAFE. So you when have a test card, you can not do much wrong. If you want to test a 50Watt tube at 50 Watt, this is your tester. Besides it is a perfect work bench adjustable power supply, with convenient banana sockets for all voltages, and each with it's own meter. Just make the right card for this yourself! Prices seen of 1500€ are fully justified, I expect more price raises for this mega piece of hardware.

FIVE STARS *****



 

"ROETEST" KIT BY HELMUT WAIGEL, GERMANY.

Originally listed as a DIY Product, I have removed it from this category, and put in under professional products, right here. This a KIT version. What is provided by the maker, is all hard to get hardware, such as the mains transformer, pre-programmed microchip, the front plate, empty printed circuit boards, etc. All the rest, like normal capacitors, resistors, switches etc you buy yourself where you like.

"RoeTest" is German for "tube-test". This very nice product, is privately made by Helmut Weigl in Germany. This is digital tube tester, the most interesting one I know. This is a kit, so you have to build it all by yourself. What you see here, is a possible way it can look, as made by the DIY builders. So the housing is your own project. What you can buy is a CD with the circuits, the description, the software, plots of the printed circuit boards, a drawing of the front plate + company address who makes the front plate for you (or design your own). Printed circuit boards can also be provided to you, as well as some of the hard-to-get hardware parts such as the transformer. This list ends with the on-board software that you get burned into a micro processor which is part of the ROETEST DIY project. All of that for a price that I think is extremely reasonable.

The pleasant thing is, this tester is kind of non-compromise. It is based on a motherboard, and then simply one board for each function. So you have a grid voltage board, a plate voltage board. etc. Any problem with a board is automatically reduced to that one board only. Kind of easy to repair and easy to service. Not fo forget a FULL switchable relay matrix board. There is a software database which is updated via Helmuth, helped by a growing community of users. That database alone is fabulous. This product is really "it" when you are a DIY.

Brief specifications: Anode max, 606V 250mA. Heater 0...127V. Until 12,75V 5A. Until 127V 500mA
Test resolution 12Bit.

Extremely versatile software. Sorry, makes the AT1000 software look kind of pale. It even allows you to write batches of tests yourself. So not just one "test" but also combinations of tests which can be started by you with just one command. I haven't tried it, but probably you can include batches in other batches, and you can become very creative. There are regularly new versions updates. There has always been a relatively good upwards compatibility of older version hardware with newer software. This is also documented on Helmut's website, which at this moment is mainly in German. (Some parts are in English and Italian)

Go to Helmuths Website

FIVE STARS *****



SOFIA TUBE TESTER BY AUDIOMATICA, ITALY

This was the first commercially available computer tube tester, and it was and still is a very good machine. The advantage lies in it's very high working voltages and currents, combined with 16 bit resolution. There is no other tester that can do 700V at 250mA not even old analog tester, I do not know of one. The disadvantage is, there is no support of any kind. Only thing is, you can send it in for repair, and they can try to fix it as long as they have parts for it. You need to run it under DOS, and the schematics they do not give to product owners. This is accepted for running production, but for a discontinued product, I miss the point of this. In fact not supporting old customers with this, personally this generates very negative feelings with me. Of course this is only my personal view. So before I buy a new product from this company, I think also of the day where it will be discontinued, and I get stuck without schematics.

This tester was made for DOS only. It will not work good under windows, since it needs real time access to the RS232 and LPT1 port, and not the manipulated ports as in Windows versions. A DOS emulator solution exist, but it works not fully reliable.

What is it worth? Hard to say. Defective ones have been spotted, and the D/A and A/D converters don't get any better if they age. So the one you buy many be fine, or just as well not. Take care before you buy one. Repairing a Sofia will be not easy.

What is good and bad about it:

+++ Top class software. Curves are professional looking. Not those dull "Excel style" curves of the Amplitrex.
++ Excellent tube curves by default. (can not say this from the Amplitrex). Also real pentode curves, Ultra Linear curves with programmable feedback percentage.
+ Curves and all tube data in one test, High digital resolution, wide range
+ Perfect graphics
+ Speed! It is much faster than the Amplitrex.
+ Genius matching software
+ on-screen monitor for tube burn in
+ It can simply do more things the Amplitrex can
- DOS only
-- They are off calibration after a long time. Tube connections must be done with plugs.
- Possibly defective after short circuit
- Factory support is below my personal acceptance level. :(
- Grid voltage is measured wrong for Directly Heated Tubes. Half of the filament voltage is added to the grid, and it was not compensated in the software. (Though this would have been very easy to do)

 

Conclusion: A very nice tester, but as with all testers, the hardware issues are now there same as with vintage testers. This will get worse after many years. Consider when you buy one, this tester is not short circuit proof, but the day will come when you have a short circuit. All you need to do is, plug the cables wrong, or plug in the wrong tube, or load the wrong tube from the software, or you do all these things right, but the tube is short circuited. It doesn't have the comfortable use of the Amplitrex. The Sofia is a lab instrument for very experienced engineers only. If the the tester is broken, it may not be able to fix it. Extremely negative is for me the issue with the grid voltage error. It can not have five stars because of this.

DETAILED TEST REPORT + COMPARE WITH OTHER DIGITAL TESTERS

FOUR STARS *****



Here is the schematic of the TV11.

Superior Instruments TV10

This is a nice Emission Tester. It looks like an antique piece, but it is better than may other "later" types. Tube testes of this kind have some advantages and some disadvantages. Many Emission Testers were made and are still around. When you buy one of those, you can have one which is nice and pleasant to use, or have one that is inconvenient, and only "so so" with the results you get from it.

The advantage is easy of operation, low cost, a great many were made, and not much can be broken inside. When buying an emission tester, and you want one that is useful, pay attention to this:

  1. You need a mains adapter knob, so you can calibrate it for the right mains voltage before making a measurement. You will see that with an emission tester, already smallest changes on the mains voltage give a big reading difference. Take a Variac and try it! So if this knob is missing, you have a tester that the makers did not care so much about precision.
  2. Make sure the switch panel in the middle has the easy flip switches as with this one. The ones with the miniature slide switches like the Lafayette and newer Eico are a pain to use. You have to set the switches before each measurement, and for the leakage and shorts test you need to test each tube pin one by one, by sliding up and down each miniature switch, which is really nasty to do. So if you can quickly flip them as with this one here, it's what you need.
  3. A tester with a build in roll chart is better than one with a manual. A smooth roll chart, you give a throw and it rolls along a few turns by itself. They fool you on Ebay with that. When you need to push the roll chart, and it moves only one inch at a time... beware it is a very long roll of paper! This is hard to fix, and in the end the paper will tear and break. You may need a new NOS paper roll, and that's really hard to get.
  4. The leakage test must correctly indicate leakage with the intensity of the lamp. That is done by defining a certain leakage where the lams begins to burn. So the beginning of the glow (faint light) must be at 300...400k Ohms leakage, nothing else. When the lamp only indicates shorts, that's useless. Old tubes have no shorts, but they do have leakage. To test that, just stick in a 400k resistor at two random pins, and then try to find that leakage.
  5. The transformer must not be underrated. If the tester you want to buy is very tiny and thin, the transformer is probably underrated. Why does matter? It means you can not continuously test the tubes, and such a tester will have a "test" button. This TV10 has no such "Test" button. It has a test switch. So the TV10 can test a tube continuously, and heat it up while doing so, for instance for 10 minutes if you want it.
  6. Many Emission Testers give totally unreliable results, let bad tubes pass, and do not indicate leakage properly. Verify that with tubes that you know to have some specific defects.
  7. Make sure it has enough old type sockets.

TV10 has the same schematic, only TV11 has a solid state diode and an output for noise tests.

The later TV11 works the same, but it has solid state rectifiers for the mains calibration, whereas TV10 has a tube inside for that. Some later TV10 have Selenium cells build into the meter, making it a pre-version of the TV11. It is recommended to check all resistors, and replace them with new ones when deviation is more than 5%.

Conclusion: A very good products, this tester will do all of the above. I was amazed to see it gives CORRECT readings for a good 300B and known to be weak 300B. Honestly... very few testers can do that, no matter how expensive. Most Hickoks don't even have 300B on the roll chart, because they can't test them. FOUR STARS *****

some more information about it



After all the experiments with other companies' tube testers, and always having the same struggle against measurement errors, and limitations in plate voltage, plate current and filament current, and whatever more...... I came up with this idea. The beginning is a precision regulated 550 Volts, 180 Watt power supply from Fluke. Then the filament voltage, and grid voltages comes from Agilent precision power supplies. Add the necessary instruments to measure all you need to know, and there you are: A precision tube tester. So now I can measure the grid current any way I want, and everything else a normal engineer wants to know, apart from reading "Good tube" of "Bad tube" on a meter. Transconductance can be measured most accurate, because all I need to do is move up and down the grid voltage 500mV. The difference in plate current can be used to calculate the transconductance. Also plate impedance and gain can be determined this way quickly. Actually this is the tube tester I use for all tubes that need a lot of plate dissipation. Needless to say this the ideal tool to regenerate and burn in tubes also. The test fixture can do Octal, AD1, UX4 and UX5 tubes. The other tubes go on the Russian L3-3 tester, and for a quick "good/bad" test result I use the Funke W19. The Agilent power supplies have a memory so I can store five complete settings. Happiness comes up when using this.
 

Part 4) Not in my collection

INFORMATION (circuit diagram, inside pictures etc) WANTED:

  • TESLA TECHNOMAT
  • AVO CT163, MK3
  • SOFIA TESTER


Eico Tube tester Model 666

Eico Tube tester Model 666

Eico Tube tester Model 666, Another Add

Eico Tube tester Model 666, Another Add. It cost 109$ complete. I think a good one should be worth that today still. Original packed kits are now more expensive than complete wired ones.


Precise Tube teste, Model 111

Precise Tube tester, Model 111. Why pay 70$ for an EICO KIT when you can have this better one for 69,95$ completely build. Here you can see what a brand name is worth.


Mullard Tube teste, Card Matic

Mullard Tube tester, Card Matic


 

Wow. You made it up to here. You must be a serious tube aficionado.
Then perhaps you like
the blue glow pages