I have assembled a very poor 'guide' to assist you in repairing your Hickok tube tester. Or, you may be hesitant about buying that 'Handyman's Special' for $50 because the thought of repairing a tube tester frightens you. I would be more afraid of someone who would pay $50 for a non-working Hickok, but that's me. I've done it myself in the past, but only because it was something like an otherwise pristine 752A. You won't be that lucky, but you just never know. Unless one of the power transformers has a short or open winding, most any can be repaired; it just takes a little patience and a lot of luck. If your soldering iron is plugged in, let's tackle that Hickok!
Let's assume you have one of the 'basic' Hickok tube testers; the 533 say. If you have the manual, great. If not, download it (or any similar tester), and study it. What you should see from the schematic is as follows.
Of course, we will check the 'fuse', which is often an 81 bulb. If the 'fuse' checks OK, we continue on. Set up the tester for a 6V6 (but do not insert a tube), and check the following. Keep in mind that the 'negative' lead of your VOM should be in pin #8 of the octal socket for any voltage measurement other than the filament. These initial tests are done without lifting the panel!
We have now checked the tubes under the panel (without removing the panel screws) and confirmed the bias potentiometer is working. That last part is important, because the bias potentiometer isn't available from Radio Shack today. If one or more voltages are 'missing', we will have to open up the panel, and look around inside. Usually, the rectifier tubes are mounted to a small bracket on the power transformer. Below is a view of the interior to a Hickok 600A, showing how the rectifier tubes are situated.
Some models will make you remove the bracket bolts, and position the bracket in such a manner that voltage checks are possible. By carefully having the bracket positioned so you can do some voltage measurements (use clip leads!), press the 'P4' button, and check the following.
If all checks turn out OK thus far, you are actually in trouble! This is because you now enter the realm of the esoteric fault. I once had a Western Electric KS-5727-L1 that had multiple faults. Aside from leaky capacitors, the plate voltage was very low. A new 83 didn't cure the symptoms, nor did using 1N4007 diodes instead of an 83 (just to be sure I didn't swap one bad 83 with another bad 83). The plate voltage is fed from the 83 through a small tag board (I had cold solder joints here, so be advised), over to the 'P4' switch, as well as through to the micromho/grid signal range switch! Either switch is a pain to get at well enough to service, and chances are this is where the trouble is if everything else checks OK. There are 47-ohm resistors on three switches (buried very cleverly) that also can act as a fuses. When these 'blow' from trying to test a shorted tube, few people know to look for them. Even if you do know what to look for, you go cross-eyed trying to find them. Other odd-ball faults are as follows.
As a final check; let's assume you have a Hickok that appears to test the 6V6, but does not register a reading on the meter. Check the 'Fuse' bulb as you hold the 'P4' switch down. Does the bulb glow very faintly, and increase slightly as you hold the P4 switch down? If so, the trouble is between the P4 switch and the meter movement. Check all wiring between the P4 switch, the micromho range switch, and the meter movement. There isn't much to go wrong; some wiring, and a few precision resistors. The remaining possibility is the meter movement itself.
That about wraps up all
that I can share with you regarding Hickok tube tester trouble
shooting. Most testers I have come across have given no trouble over
their 50+ years of service, but there is always that one 'dog' to
contend with. If I am looking over a prospective purchase, I check to
see that all of the panel screws are in place. Missing screws almost
always points to the fact someone else took time to 'fiddle' with the
innards of that Hickok, and only Jehovah knows what they have
'screwed up'. For $20, I have taken the gamble, if only to have a
cadaver to donate organs so that another Hickok may live
again. But, thanks to the magic of eBay, even beat-to-crap,
non-functioning Hickok tube testers can now fetch $125
or more, and some neurotic tube jockey still feels he is
getting a bargain. I recently witnessed a Hickok tube tester
with no meter movement, no bias potentiometer, and a
case that looked like it had been dragged behind a team of wild
horses offered for auction. Don't bother asking what the final
selling price was; anyone offering over $1 should have their head