Does this mean my 21AXP tube has gone to AIR???
 

I spoke about this on another thread--but i am not sure anyone saw it.

I picked up that CTC 4 set in Wheaton Ill, On Sunday. Me and Doug Harland huffed and gruffed it out of a basement, up some difficult stairs. I hoped the tube was ok, because the owner says the last time it was on--it DID have a good pix, then lost vertical. BUT..that was about 40 YEARS or so ago, he thought. Still--I had high hopes, since my last 2 sets with AXP tubes have both had excellent tubes.

SO--I tested it yesterday on my CR-70. This tester works VERY well, and has NO trouble testing color roundie tubes. but on THIS tube...the fils. will NOT light...AND it seems to be OVERLOADING the fil supply on the tester--because the meter will NOT go above 4 volts, even WHEN I turn the fil knob to 8 volts !! Also--the tester is making a MUCH louder whine than usual. The neck IS getting pretty warm after about 3 minutes--but it will NOT glow at ALL.

SO--does this mean the tube is FULL of air? I take it to mean the fils can't warm up enough--for the current draw from them to drop to normal. But I do not really understand WHY the fils will not light-...if i air---even WITH full--or even excessive--voltage on them ?? I would not think a bit of air would cool them THAT much--to keep them from glowing--or WOULD it ?

Are you using the universal adapter? If so, are you on the correct pins...

Can you test it with another tester to be sure?

If it went to air, most likely the filaments would glow - very briefly before opening.

Cheers,

I tried it both ways--with the big socket AND the uni adapt. NO difference.

The tester DID work later on another tube.

I KNOW the 70 has a current-limited fil supply, and it seems to be limiting it--likely due to too much draw.

If you try the tester side by side with a known good tube and it works and then just move move the socket to the 21AXP22 and you cant get the filaments to light I would say the tube is bad.

did you try testing for shorts (even with the filaments not lit).

Just for fun, check the resistance of the good tube to the 21AXP heaters.

But WHY--won't filamants in air glow?

i HAVE seen this before--but don't fully understand it.

Filaments in air will usually burn out.

The neck getting warm sounds like something inside the tube is shorted out.

.

Because air conducts heat away from the heater much better than vacuum... that is likely why the neck is getting very warm.

IF the full 6.3 volts is applied... I think that the cold resistance of the heater is so low that the tester voltage sags down to a lower voltage.

jr

That sounds like what happened when I tested my gone-to-air 21AXP22 on my Sencore CR70. The filament had continuity but the tester made unhappy noises and I got no hint of emission.

I was told to look at the little peek-a-boo slots on the neck. There, the getter looked white -- a sign that the tube had leaked.

I was able to substitute a newer 21FJP22, which you can read about at http://antiqueradio.org/RCACTC-4ColorTelevision.htm .

Phil Nelson

http://antiqueradio.org/art/RCACTC-4CRTGetter.jpg

http://antiqueradio.org/art/RCACTC-4CRTGetter1.jpg

Is it me or do those guns look rusty?

SR

Yup when an electron gun is in a tube without vacuum for years it will rust.

Plug the heaters into a big 6v wall wart, if they burn out you have your answer. It's probably bad, the one in my 4 was a dud when I got it.

You mentioned having another tube which the tester worked fine on. If that means you have another set, just position them butt to butt and hook up the socket from another set. See what happens.

B.T.W. I am fairly certain that Mr. Thomas Edison had some of the same questions with the early incandescent lamp. A quick read on that would answer questions about why heaters burn out in open air. That aside, I don't get why a tube without open heaters and gone to air would do much of anything more than give you a momentary light show before pretty quickly opening up presenting NO load to the test instrument.

Perhaps these old things are more robust than I give credit for. Phil Nelson's story contradicts my thoughts all together. I don't think anyone mentioned the number of times these tests were done; or duration. Seems like it would be a one time thing....

I didn't keep time with a stopwatch, but I tested the tube multiple times, for a few minutes each time. I didn't want to believe it was really bad, and I have had a number of tubes that gradually "woke up" after sitting on the tester for a while. I also tested the filament for continuity more than once, again, not wanting to believe my eyes. The white getters convinced me I was wasting my time on a gone-to-air tube. The visible rust on the tube elements is also consistent with air (and moisture) getting inside.

That's a sample of one, so take it for what it's worth :)

Phil Nelson

Makes all the sense in the world. :thmbsp: I am hoping that my statement, "Phil Nelson's story contradicts my thoughts all together. I don't think anyone mentioned the number of times these tests were done; or duration." was not misconstrued as being flippant.

I meant it as a general thought on the thread and the info. we had at the time. The number of times tested was more toward the thread starter, and the rest just my surprise that the heaters don't just burn out pretty darned quick, so I questioned duration on RCA2000's tests.

Phil's deduction of his tube gone to air with the rust and white getter inside. I pretty much write anything with white getter to be pretty much garbage. No harm done I hope.

I had a 21FJP22 that had worked fine. After years of storage I tried testing it one day and got similar results. After looking carefully I could see just a dim glow from the filaments, before watching them burn out one by one. A sad thing to watch :(