Today's Mystery Guest (RCA CTC-4)

[miniman82]

The gun isn't the problem, it's the shadow mask. If that has rusted or deformed, the tube's junk no matter how many guns you put in it. Getting the old gun out would confirm the extent of the damage, as you'll be able to see down the neck and have a look at the condition of the mask.

And yes, I can weld these tubes successfully. If there's a leak, it would be a lot easier to fix than on a 15G. With the 15G you'd have to frit treat the glass/metal joints first, then weld the metal seam of any pinholes.

[ohohyodafarted]

Phill,

Leave it alone. Don't mess with it. Just put it in storage in your climate controlled home until such time as it may be a candidate for restoration. It is still sealed good enough that it is better than anything that you could possibly do to improve the situation.

Moisture is likely not the issue. The tube has O2 inside, and when the gun was heated via the filiment, the metal on the gun reacted with the O2 and caused oxidation of the metal in the guns elements. If the filiments had not been heated in the presence of the O2 in the tube, then it is very likely that the gun elements would not have oxidized.

Anyhow, no harm done. The gun is toast in any event and would need to be repaced or rebuilt if the tube is ever to be rebuilt after fixing the leak.

Best way to get a usable 21AXP22 is to wait for a clunker CTC5 to surface to steal the crt out of. The 5's still surface once in a while and I would personally rather have an opperational 4 than a clunker 5. The 4's have a better picture quality.. I have actually trashed a crappy 5 and made a 21AXP22 test jig from the crt, and associated cabinet components. Some day I will likely use the crt from the test jig to restore a worthy set needing a 21AXP22.

Be patient and sooner or later you will come by a decent usable 21AX for your director. I would presonally NOT do a retrofit with a glass tube. But that's JMHO, and my way of doing things. I would rather have a correct bad tube in a display set than an incorrect tube in a functioning set.

[Phil Nelson]

Thanks for the advice. If I can fit a glass tube non-destructively and watch the TV while I'm waiting to find the right tube, that would make me happy.

Does anyone happen to have the RCA factory manual? I have the RCA field service manual and an RCA service data supplement, but not the manual itself (Service Data 1955 no. T5). These docs (plus Sams) give me enough info to restore the set, but you never know what handy little tidbit another manual might include. I'd be happy to pay postage & a reasonable fee to borrow one for scanning.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[Phil Nelson]

After replacing the electrolytic & paper capacitors, plus assorted resistors, the chassis passed the smoke test and has reasonable B+ and filament voltages. After I lay my hands on a couple of new tubes and oddball caps, I'll be ready to try more interesting experiments.

Looking ahead to when/if I get a usable 21FBP22, I gather that I'll need to fabricate a new HV lead for the CRT 2nd anode and make some provision to prevent arcing from the anode button area to nearby hardware. I'm hoping to use the same yoke and other neck whatnots, since nothing else is available. If that's a false hope, someone tell me now!

Phil Nelson