No grounded Deck
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Safetiy Issue #1. This the most imortant one, when you use a Hockick with an 230/115V auto transformer. In the USA, the mains voltage is 115V and in Europe 230V.
230V is not twice as dangerous as 115V. It is many time mores dangerous. With an electric shock, there are two things that are not so nice. At 230V you can burn your fingers, but I had that so often. That will cure. The other is, you can get a heart stop. When you get an electro shock, above 60mA through the heart, it stops beating until you get an injection with insulin. For getting that kind of current, all you need to do is touch a metal surface that is under high voltage. Now with very old Hickoks, it is nothing unusual if the mains cord breaks off the potentiometer, and then touches the metal deck plate. It happened to me.
The Hickoks have no grounded deck plate, and this can be very dangerous. The deck plate is floating, so to say not connected to anything. The isolated deck plate is some kind of safety, but obviously the thing and it's safety levels is for 115V only, by 1950's standard, and now the wiring is 60 yeas old. So you have a very dangerous situation here.
Let me tell you why you should always ground the deck plate. The mains cord is connected with one wire, in a very clumsy way to the Rheostat, for the mains control. With some of the testers I have, it broke off already, and I just re soldered it without much thinking about it. The other wire to the switch, is connected a little bit better. It is just a matter of opening the tester up many times, and one of the wire breaks off. Then it may touch the deck plate, and when you use an auto transformer from 230V to 110V... you have a 50% chance that the hot 230V end touches the chassis, depending how your auto transformer is plugged in. So you may be firmly pushing with your left hand on the metal plate, when you want to get out the tube you're testing. If at that moment the wire breaks off.. you go to tube heaven. Short before the wire is breaking off, it is hanging only on one last and single strand, and your tester will behave funny. So I was trying to find out what's wrong, put in a voltage regulator tube, and let it draw 100mA from the tester. It made the fuse lamp glow even.
And then it happened to me, and thank GOD, the previous owner had grounded the deck plate, with a new three wire cable. So the "hot" wire of the 230V was grounded at that moment. It blew out the fuse of the whole floor. No damage whatsoever to the tester because the hot 230V lead came straight to the grounded deck, not to the inside guts. Only imagine what could have happened. So I can only very much advise yo u..... When you use an auto transformer, NEVER EVER work with Hickok before grounding the deck plate. |
DANGER!
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Safety Issue #2. This is not a joke! With the bigger models, the mains cord is protected from being pulled out, with a nice metal ring. It works. HOWEVER when you push in the cable, you push in the ring as well. Stupid enough, the position is just below the mains transformer, and if by coincidence you push in the cable more then two inch, you touch the high voltage contacts. So remove that ring, and connect the cable another way.
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Scale of 750 Tester
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Most Hickoks have in addition to the micromho scale, a so called English scale. Now I don't know what's so English about that, but with this is meant the good/bad scale. The micromho reading for those is what a new tube should read, and the good/bad scale gives the reject point. |
English scale: |
Some of the larger testers have only the micro mho reading, and no good/bad scale. To allow you to judge a tube for it's quality, the give the reject point on the roll chart, not the value for a new tube. This is very very confusing. So the when the 750 says, that 6L6 tube must have 5000micromho, that means a new tube. A used tube may be below that, as long as it tests in the green of the English scale. For those who are interested, I tested this with the two 750A I have, and the reject point on the micromho scale appears to be 4000 micromho on the one and 3500 on the other. This is in-line with the 70% that is used at the real laboratory testers like L3-3, or the better Emission testers like Funke W19. |
Conclusion: |
The micromho readings in the roll chart is not the same, for the above reasons! |
Test signal |
The Hickoks use an AC Test signal, which is connected to the grid. It is obvious that such tubes that need very low grid voltage, can not be tested accurate since these can be fully overdriven. Some the testers like 533, 600 or 605 use a fixed 5Volts AC, which is too much for some tubes. The later 533A, 600A, 605A, 800, 800A used 2.5V, and the more versatile models like 539, 750, 752 used variable voltage from 0.25 to 2.5V depending on the Gm scale you choose. With those testers that have variable test voltage, do the testing only on the sensitivity as indicated on the roll chart for the tube, or you might by mistake be testing the tube in overdrive condition. So if you have to test it on the 15.000 scale, and the reading is too low, the tube just bad, and is not better than that. If you go then to another scale to get more resolution, you may be overdriving the tube, and measure a fully wrong result. |
Spraying contacts |
There are so many warning for this in the internet, saying it can damage the whole switch. Perhaps this is possible, but never had a tester with damage like this. |
Calibrate your Hickok |
My opinion? Don't try it, unless you really really know what you are doing. Don't ask for email support with this. It is too much techno babble. |
Testing 6DJ8 (ECC88) |
This is a difficult tube to test. From some tube testers, like the 600A there were errors on the roll chart, right from the beginning, and never cured. The correct setting for the 600A is 24. |
| Tubes not on roll chart |
Getting the latest roll chart may not help. The roll chart has a maximum length to be practical. So in many cases, obsolete tubes had to make room for newer types like TV Tubes. For instance the 27 was removed, because it was already obsolete in 1950. While today it is a nice hifi tube, you need to get the "obsolete tubes" data. It exists for many of the Hickoks. |
Sticky meter repair |
Only do it when you can repair a watch. |
Open meter repair |
Check if the internal resistor (wire wound spool) has a bad solder joint, or if it is really the meter. When it is the meter, there are sometime slide contacts in there, that have to do with the set screw, on the front panel. You can oil the slide contacts, or just slightly spray the area where the springs are (top and bottom), and after that move the set screw a few times. Open meter spools are harder to repair. leave that up to specialists. It can be done. |
Electrostatic charge |
Careful when polishing the meter plastic cover, this will charge the plastic, and the needle can be heavily deflected, like 15° . After polishing just wait, and it will go away. |
Different results on different testers (1) |
Some testers print the Gm value a new tube should have on the roll chart. For good/bad you must use the English scale. Such testers that don't have the English scale, give the reject point on the roll chart. |
Different results on different testers (2) |
You may not have expected so, but it is normal. What you read on the meter, is NOT to be compared with a tube book, and NOT with other Hickok models too. You must always go by what it says on the roll chart. Only when you have two of the same testers, readings should be within 15%. |
White "rust" powder on chassis. |
Be careful with the white power, which is like a dust layer on most older chassis. I don't know what this is, but I hope it is not cadmium plating. That was thought to be "not so" poisonous, until now we know better. If you have a chassis like that, clean it at a windy day, outside the house. It can be removed very well, but don't breath that dust. I don't know what it is. |
50Hz or 60 Hz? |
The Hickoks are made for 60Hz, only the military types can work until 400Hz. There can be an issue that when working at 50Hz instead of 60Hz, the fuse lamp may start to glow very little at ideal, not testing a tube. This should not be the case at 60HZ, but at 50Hz, it can happen. It seems to have no effect for the rest of it. |
