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 :)

In a few words: A fully underestimated tester, secret tip. I see people pay 220 Euro for "low end" Emission testers. I don't think these are worth that at all. Then you better pay this price for a Mk1!

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

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. .

Manual of AVO Mark2

AVO Mk4

This is the most sought of, and most wanted tester. Mk4 has some small advantages over the Mk2, like more precise reading of the scales.

We have to say it, that this extremely precise way to read the numbers from the scales is marketing only. The resulting precision from a measurement doesn't come from extremely precise scales, as long as the base precision of the whole machine is not better than any other. I found the M4 and M2 having the same precision, really no difference, and I have two of each, so I can know.

Mk2 has the big advantage of much higher negative grid voltage if you need it. (and oh yes, you need it) . The case of the Mk4 is stronger, end certainly nicer looking. But .... Mk2 is easier to service the inside, because you can lift off the whole cap. So for me Mk2 and Mk4 get the same score. Still either Mk2 or Mk4 are not as accurate as CT160.

So here is how I rank them:

Simplified user's guide to the Mk4:

1. Mains test: Set Circuit selector and leakage switch to the left position. The meter now will go at or close to the red ~ sign. Set meter on the ~ sign with the "set ~" knob.
2. Do all settings by the book, for the tube you want to test, set back off knobs to zero, and Meter Switch to 100mA, and Insert the tube. Generelly the rotary switches are now moved to the right, depending on what you do.
3. Select Check (H). H stands for "hot" Tube will burn now. If not, stop here.
4. There is also a way to test the filament of a cold tube, but I prefer to see it burning myself.
5. Let the tube warm up 60 seconds. Turn the leakage switch step by step to the right. If any position shows leakage, stop here.
6. Select " C/h insulation" to test cathode to heater insulation. Read on the upper scale in Meg Ohms. Below 400k is a problem, but most tubes will show no leakage. If there is leakage, select Check(C) and see if it goes away while the tube cools down. This conforms the leakage, stop here.
7. If all above tests passed, select "test" and read the plate current. With the normalized Ug1 (by the book) check if the tube has the normalized plate current +/-30%. If more than +/-50% off, stop here.
8. Check if the tube responds nicely to Ug1 changes, and set the tube for the expected plate current, as by the book. WIth this normalized (by the book) plate current you must test the transconductance. THIS IS NOT AS AVO WRITES, IT IS A BIG MISTAKE OF AVO, SORRY.
9. TRANSCONDUCTANCE TEST:
10. Wait now until the tube is stabile, so plate current is not rising any more. This can take a few minutes.
11. Turn the left back off switch until you have just above zero on the meter. .
12. Turn the right back off switch until you "zero" on the meter.
13. Turn the "meter switch" step by step to the right, re-adjust the right back off again. Final adjustment is at 2.5mA. Make sure the meter is stabile now and at zero. (tube is fully warm)
14. Now select "mA/V" and the meter must be in the green, and basically you're done, the tube is good. Ideally the meter is at "1" meaning 100% of the value selected on the turn wheel. At -5 it is 50% lower than on the turnwheel, etc for all other readings.
15. You can also measure the actual transconductance precisely with the mA/V turnwheel. Just turn the wheel until the meter is at "1" and read from the wheel the actual value of the transconductance. This must have the same result as the previous method, only the turnwheel method is more accurate.
16. As a final control, select mA/V again, and check if the back off is still at zero. If not, you must set it to zero and start again. To prevent having to start again, do the mA/V test quickly. If you are routined you will learn to appreciate this method.

MK4 METER PROBLEMS.

The meter of the k4 is a specialty, and a little bit a design mistake as well. They should never have taken it. Let me explain this better. This meter is a 30uA with very low resistance. It has 3250Ohms on the connections, but the movement is even lower resistance. Then, it has a quite long needle, and the needle is a bit too heavy weight. Such meters are not even made any more today. You can buy 30uA meters, but these have 4...6 k impedance and short needles. Due to the heavy weight of the AVO needle, the meter is too sensitive to damage. So if you overload it, it violently shoots against the needle stop, and something breaks off inside. Also they are not dust-proof any more after all those years. The glass is kitted with some stuff that gets brittle, and from the inside it is also not dust proof any more. So all kind of particles come inside, and most attracted are of course the magnetic particles. Mostly after shipment those find their way into the magnetic system, and there you are, another one of those infamous sticky meters.

Also the meter is so extremely sensitive for no reason at all. The only thing they achieved was a scale for the leakage, which can precisely measure 25 Meg Ohms. But what the heck you want that for. I mean do you really? So what tube is that, you MUST know this about? And what is your minimum acceptance value? I bet you don't know. Well, it is 400k normally. Any tube, new or old with less leakage than 400k is considered good. So only because of this (useless) very sensitive leakage measurement, they choose this very sensitive, easy to destroy meter. Another big advantage is, these extremely sensitive meters function by means of extremely strong magnets, and what happens after 50 years? Right! They loose magnetism. So it is completely normal if a Mk4 meter indicates 10% less. The crazy situation is, you calibrate the mains now 10% too high, and with that, the tube reads 10% higher. Or 25% higher, or 5%, or whatever. You can easily find that out if you put a true RMS Amp meter in the current link for the Anode. It must indicate 50% of what the meter says. Well you are a lucky man if this is so indeed.

So.... don't buy it with a broken or sticky meter. You'll n-e-v-e-r find a replacement. Best thing you can do is buy a broken CT160 with a good meter and sell the CT160 without the meter again. The internal system is the same. However opening such a meter means magnetic dust can come in, and you damage the concentric springs or needle bearings before you know it. Only recommended if you can repair a watch. If magnetic dust gets in, don't try to brush it out with compressed air, that kills all piece parts. Cleaning can only be done if you remove the magnet, which involves taking the whole damn thing apart, and from that other problems can arise. So also replacement meters, before you buy one, should be originally closed.

Mk3 and Mk4 do not differ so much. Important is the nicer dial wheels with the Mk4, and the very sensitive Meter of 30uA full scale. Same meter as my favorite, CT160 has. Even today such a meter is not to be found, with this low current and (only!) 3k impedance. IF YOU KNOW WHERE TO FIND A NEW MADE METER OF 30UA and 3K impedance or less, with a nice, long pointer needle on it, please contact me, I will be happy to place that here, since very good DIY might be able to repair blown up Mk4 and CT160 meters with it, and mount it underneath the original scale in some way. . Best I have found is 30uA 6k, but that will NOT fit into the circuit nicely. Lower current and/or lower impedance is fine, of course. That can be adapted with resistors.

You have a broken meter? It can happen when you make a set up mistake, and the needle hits the sides violently. It is not very protected against that. Also some meters stick a little bit, or can be electrostatic. Here is a company in England that was SAID TO repair PERHAPS (??) AVO Meters. It's a normal industrial company, so don't expect any interest in tube chat. Here is an English site where you can discuss old equipment.

The Mk4 service Manual HERE
The MK4 operating manual HERE
The BIG AVO Valve Data Manual 11th. edition. HERE

A bit of a crazy project, but turns out very interesting. Look here.

AVO CT160

Is operated in a very unusual way, because you have to balance a bridge for the measurement. However you get used to it quickly, and once you are you start to appreciate it, given that you know what a bridge is, and given you know what you are doing. If these two things are not given, you won't like it.

It is quicker to operate than the Mk2, Mk3 or Mk4. CT160 is amazingly very precise but ONLY AND REALLY ONLY when the internal calibration resistor is awfully precise adjusted. Any yes, when it's older it needs to be replaced. Also the grid pots usually need a repair (that you may not know). These are the weak spots, and quite easy to fix. For the rest nothing serious can be broken inside. However a repair on this one, same as with any tube tester, is no job for amateurs. For a detailed test report, click here. 

In a few words: Amongst the top-ten testers.

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

Centrad 752

Will describe it later, looks a bit like a Taylor 45. It is defective. Need to repair it first.

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.

In a few words: Ideal for for who want to get a very quick and reliable result, which is totally respected by the everyone.

WARNING: A Quantity of about 50pcs NOS, original factory carton packed W19 have been removed illegally from a warehouse in Germany just a few years ago. By German rights, you can not become the legal owner of stolen goods. Under all circumstances, the legal owner can claim back the goods from the person who owns it.

Read more about the W19

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

Picture from the patent

Grundig Tubatest

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

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.

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?

Heathkit TC1 Tube Checker

A tube checker is a category below what we call a tube tester. It is from the days of TV's mostly USA color TV's. It just checks is the tube is having a basic function ir not. It tests all tubes as a diode, at just a few mA. So not a very good test. In most cases, TV defects are always the same. Like a broken tube filament with just one of the tubes, but they all in series. So all tubes stop working. So if the TV is dead., first you relplace the fuses, and if that doesn't help, you pull out those 10 tubes that you sort of know they can be bad, and check them all quickly with the TC1. That t costs you 20 minutes for all tubes, but when you find the broken one as the first, it costs you only two minutes. You can repair 60% of all TV's by just replacing the broken tube, and/or a fuse. This is what this tester was intended for.

People tend to pay unreasonable prices for such of those testers that appear very nice optical condition, like up to 300 Euro. I I can not believe what I see. They think it's a tube tester, which it is not. I mean you can pay a collector's value for it, that is your own choice. Just do not expect something useful from this device. Before you pay 300 Euro for a useless tester, you better pay 3x as much for a Funke W19. That is also a tube checker, but the best one ever made, and you can trust it's readings blind.

Overview of Hickok Tube Testers

You can devide them in five groups.

1. Models before the Hickok patent

very old testers, not practical today.

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 like the 539 models have even a separate filament transformer, and very good calibration possibilities. Hickok was never succesful in this market, which was dominated by RCA and Weston.

5. Cardmatic testers

Parametric testers. Works with tube stabilzed voltages. Magnificent products, but with small interest, because they are full of electronics. There is a man in the USA re-building those with a computer interface.

Hickok known issues, problems and general information

Link to official Hickok company photo archive

Robert D. Hickok died in 1950, and was succeeded by his son, Robert D. Hickok jr, who bought Superior Instruments in 1959.

KALIBR. Model L3-3 from 1986

The L3-3 is the latest model, and it has silicon rectifiers in it, but all electronics is with tubes. The L3-2 is similar, but has many tube rectifiers inside.

This is one of the most amazing testers I know. When I bought them, the tube tester market was not so over hyped as it is now, and this tester was very unpopular.

When you use an old instrument, with power electronics it, you will know you need to repair it sometimes. Something breaks here, something is 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, and 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 fine right out of the shipment box.

My L3 never needed never any repairs at all! Simply none. Only service, like a defective control lamp or a bad socket contact. All capacitors are still original. The rotational switch for the leakage current has ceramic decks, and are all shiny like new. In case you ever do need to repair it, you need to know this: First, you probably won't be able to read the Russian manual. Second, you don't need it at all. The schematic is very well drawn. They didn't try to to make "clever" schematics, but one that normal people (like me?) can understand, and it's all on one huge sheet of paper (size of 80cm). The the tester can open from all sides by means of perfect mechanical systems. Each wire is numbered, and the number is on each wire with a small sleeve. Third, the electronics function has no patented crazy circuits that nobody understand, like in all Hickoks. Instead you will find straight forward electronics, nicely arranged. It has printed circuits for the oscillator and the regulated power supplies, and free wiring for all "heavy" stuff. So anyone can understand it, when you understand a regulated power supply.

Detailed picture. I have two of those, so I can measure large numbers of tubes faster. While checking the readings on the one tester, the other one will warm up the next tube already. Like this I can work really quick. It is a fully programmable tester, by sticking pins in the pin board. All voltages internally stabilized, Max 300V, 100mA for the plate, and 2x 10mA for the other adjustable power supplies.    It features an internal 1600 Hz oscillator,  and a tube microampere tester with 2nA resolution (0,000000002 Ampere!). For perfect leakage measurements, the heater to cathode voltage can be programmed. Also the internal tube screen that separates double-triodes like some ECC....types, can be tested for leakage. The leakage current can be measured very precise, and also the voltage can be checked at what the leakage will start to begin. Tubes filaments can be heated with fixed voltage AC or fine adjustable DC.  Like in real amplifiers! 

A very special feature of this instrument is this: You can program an Single Ended circuit for the tube under test, choose a the power supply capacitor for the rectifier, selectable a cathode resistors,  and the bypass capacitor. This is not the only circuit diagram feature. With an internal 1600 Hz (distortion free) oscillator you can test what the tube does, and make AC measurements. Wow! Can you imagine what a machine this is? It took me 3 weeks to understand most of it. It is constructed with printed circuit boards. Most of the electronics is with tubes, and some solid state components. This is the most versatile, and most precise tester I have seen so far.  I was lucky to buy one 1986 model NOS. I am the first user of it. Most calibrations can be done on the front panel, using the front panel meter. It can work on any mains voltage from 100...380Volt, and even 400Hz mains as used on ships and airplanes is possible. There is nothing you can NOT do with it. 

Disadvantage: You need to make your own test cards, Because it is supplied with a set of useless test cards for Russian tubes that you will never use. You should use those cards however to find out how to do it. So many special measurements can be done. Some tubes like 6L6 or 6SN7 are included, but most of the supplied cards are useless, and most of the audio tubes are missing. However, any card can be made, with any circuit you like. So once you have managed to make a good test card for an ECC81, you can easily construct all similar cards from this. I found some of the original cards are not constructed fully logical. For instance they often program a 6Volt tube with an adjustable 3...15 Volt filament. So you can burn the filament by mistake. I made my own cards, that set the 6Volts filaments for an adjustable 3...7 Volts. 

Lifetime and stability. I have one NOS, and this one is more stabile on the Zener stabilized voltages for the Grid1. For the rest I see no difference. With the NOS, the Grid1 voltage needs no more adjustment after one hour. It stays stabile for the rest of the day, whereas the used one needs three hours for that. I mean here adjustments in the 1% range, as fine as the meter can indicate. So you see again here, NOS has some advantages. The tubes in both still the first, original factory tubes. I have about 5000 on both testers now, and all original tubes still inside. I can use one tester to test the tubes of the other.

Some notes, when you want to buy one: I do not know how many of those testers are on the market, but I see several people selling real NOS ones. These can be very good, even though the inside piece parts seem to have an oxide layer here and there. As far as I know, there are no parts inside that suffer from that. The critical part, the tube nano-ampere meter and oscillator are on one PCB that is dip-lacquered, and the leakage switch has ceramic decks. Such an NOS tester is more recommended than a heavy used one, since a used one is not much cheaper, but has issues any used tester has. So a NOS one, with the original spare tube set is the best buy, ideally in the original wooden crate. Then you have best chances it is NOS indeed. I definitely do NOT recommend to buy any other model than L3-3, so not L3-1, L1 etc. These can be a lot older, have tube rectifiers inside, get a lot warmer, have older components inside, and have seen a lot more use, and are sure not NOS. The market price of a good L3-3 is based on the fact that somewhere some people have an NOS stock still, AND the tester is a bit of a secret even now. However both things will change. So one day many will know this tester, and NOS stock will gone. It is the ever repeating NOS tune, like from a record with a crack in it. When it's available all want to "wait". And when they are gone, they bid like crazy on Ebay trying to get the last not-so-nice one. But... it's normal. It's the world of NOS. This tester is better than AV= Mk4, and for that they pay 1600€.

L3-3 in a few words: Amongst the top-ten testers, best buy for the money.

Russian Handbook

FINALLY! The English translation (much unfinished)
Google will not translate better than is does, but it is improving every month. So if some texts look strange, try again in 6 months.

Calibration procedure as used by one of our customers

METRIX-U61B

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. 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.

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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 enough muscles to carry it. Disadvantage is the unstabilized voltages, and older type sockets are not available. However it is one of the few (or only?) 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. Price of 1500€ is fully justified.

Superior Instruments TV10

This company was bought by Hickok, in 1956. So sure they had good technology. The TV10 is a good working 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:

Superior Instruments made very good products, this tester will do all of the above. Though it's a very old type, it's a good tester still. 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.

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