Tube tester shot craps?

[ldervish]

My NRI / Conar 224 tube tester suddenly began sending every 12AX7 tube to the bottom of the red zone, even ones which showed 'good' on previous tests . I haven't tested any other tubes since this happened, it just seemed like something was amiss and every test would be suspect. For a while before it began doing the "instant" deep six, it would occasionally dip into the red zone then climb well into the green when "TEST" was pushed.

I know these are just basic emission testers and aren't the end-all/be all but it helps a bit at a reasonable cost. So I'm wondering, could the issue be something as simple as cleaning the contacts on the "TEST" button or is possibly something more serious? Where would I start looking?

I wanted to ask before peeking under the hood...perhaps there is some other maintenance I should do?

[nashvillebill]

I don't know about that particular tester, but some of them use two small incandescent lamps as part of the test circuit. Perhaps one lamp is burnt out, or the lamp is not making good contact. If one is burnt out, it's preferable to replace them as a pair (same manufacturer). Also some other basic maintenance may be required, such as replacing old electrolytic capacitors or paper coupling caps.

edit: Oh, it's an emissions tester: likely would not have lamps then....

[dumbassbob]

My switch was full of contaminece(crap)I shot a alot of Deoxit into it,and resoldered a few cold solder joints also clean the pins on the 12ax7 and the el34-6l6gc...You may need to spray out the Test On Off switch a few times It now works good enough to let me know if a tube is still "good" or send it to All tubetesters.. in southern Califoria They will make it like new for $150.00 I wish I had the money for a Orange tubetester but over $300.00

[g1]

Manual/schematics here:
http://bama.edebris.com/download/con...bly_Manual.pdf

[ldervish]

Thanks so much to all of you…I think I have enough info now to dive in there and see what's going on. The manual/schem is a real bonus.

[Bruce / Mission Amps]

Thanks so much to all of you…I think I have enough info now to dive in there and see what's going on. The manual/schem is a real bonus.

As a hobby of sorts, I just to refurbish vintage tube testers and calibrate them.
Many times this problem is a bad connection on the switching circuit that supplies the different filament voltages to the tube sockets.
The "life test" of most all these testers is really a switch the lifts or switches the filament supply from the current test setting, to one or more lower filament voltages... that will make a lousy tube take a dump right away.