tube testing newb

[Patrick620]

On an 80 rectifier tube I should be getting two plate readings, correct? I'm using a Precision Instruments 920 tube tester and I only get a reading on one of the two tests for this tube. I got the identical readings on another 80 tube. I dont have a working radio to see if they actually work or not. The button that I have to push on the tester for the plate 2 test works on other tubes so I dont think its the tester. The readings are well into the "good" section on plate one and nothing at all on plate two. The tube filaments are lit.

[electroking]

You may have a poor contact at one of the plate pins. Or (less likely but possible)
the cathode in one of the halves of the tube may have been damaged by excess
current, while the filament did not open. Do the two halves of the filament
(visible at the top of the plates) look the same color when the tube is heated in
the tester? Good luck.

[Patrick620]

Yes, both filaments look the same when lit. I will check the socket on the tester, too. I just wondered if it was normal for half of the tube to be bad and what were the odds of both 80 tubes reading the same way. It made me start thinking it may be the tester. Thanks for the reply

[Phil Nelson]

Have you done any restoration on the tester? Vintage testers require routine restoration (including calibration), just like vintage radios.

Phil Nelson

[electroking]

Sorry I misread your original posting. Of course, it is very unlikely that two random
tubes would read good on on side and bad on the other. There may be a poor
contact in the tester. If you can grab a 5y3gt tube (electrically the same as a
80, but using the octal base), you might determine if the socket or the switches
in the tester are faulty. Good luck.

[radio63]

You may have a bad or dirty switch on your tube tester. The tube checker should be taken out of the cabinet and checked out. The switches should be cleaned with something like Deoxit. I have a Precision unit that has had dicey switches in the past that required cleaning. Also a general inspection of the tester to make sure there are no damaged parts or obvious problems is a good idea.

Gilbert

[Patrick620]

I did successfully test a 5y3gt at the time all of this happened. (I had the same thought, that this would check the tester) It uses the same circuit button "C" on the tester. This button worked on the 5y3gt test and gave me a good reading. I have not done anything at all to the tester to calibrate or restore it. It always seemed to work fine from the start. I will have to open it up and clean/inspect it. Thanks for the help.

Patrick

[Patrick620]

Ok, I opened the tester up deox'd it and in the process discovered that the 80 tube inside the tester had a loose piece of solid "silver" wire floating around inside the tube. I replaced it with one of the 80's I was originally trying to test. Same results. I jiggled the tube being tested and found that the socket must have a loose connection. By jiggling the tube, I was able to get a reading. Ok, I then noticed in the tube being tested that there are these white strips of material loose inside the tube. They have obviously flaked off of something inside the tube. The tube is well mirrored, still, and tests good. Anyone have an idea what these white "strips" could be? Thanks.

[leadlike]

I've had bits of silvering material from the getter flake off of older tubes (preoctal tubes from the early 30s mostly). Never had it affect tube performance, but I wouldn't shake that crap around too much as it could result in an interelement short.

[gadget73]

Could be some of the cathode material has cooked off over the years. I've seen some rectifiers with powder inside from this. I generally ignore it as long as it works properly. I've got one 80 tube thats been in service for 81 years now. Its got a bit of powder, but the radio still plays.

[toxcrusadr]

Some tubes have mica spacers inside that can break apart too. It's an insulator so if it's that it shouldn't be a problem.

[Patrick620]

It looks like it very well could be mica. I wont sweat it. Thank you.