RCA 21CT55 #8802897 is Dead

[stromberg6]

Originally Posted by Tomcomm

Hey stromberg6......You're right on, the 6DQ5 and 6CB5 are electrically identical! The local elect store has them for $22. Mechanically its perfect, all I have to do is interchange the 2 grid pins with the 2 screen pins. In fact RCA used the 6DQ5 with my new FBX thru CTC12 then switched to the 6JE6 in the CTC15 with the same FBX. If this doesn't calm the ultor out of the mid 40KVs, I'm at a loss.
Thanks a lot......Tom

Your welcome Tom. I just looked at the RCA manual, and the specs for the tubes 6DQ5 and 6JE6 for practical applications are identical, only a few minor differences, and the 6DQ5 looks like an excellent sub for the 6CB5, but for the connections at the bases. Interesting that the pin outs are different, perhaps to prevent quick swapping, protect patents, or to generate service revenue when uninformed techs subbed one for the other lol.
Let us know how the swap works. Hope it all comes together the way you want.
Kevin

[Tomcomm]

doogie812.........The FBX I'm using was intended to have the EHV rect on the top of its HV doughnut. Any loose fit would produce a continuous arc that could take the FBX out. The CTC2B FBX had a HV lead and tube cap. I cleaned all the HV grease out and removed the little hooky spring. I then quickly soldered a tined spot on the large output contact area and tack soldered a EHV rated lead wire and cap going to the original EHV rectifier. I then completely filled the output cap cavity with RTV silicon. Works fine, but at an occational 40+kv non loaded run with no 6BK4 reg the little 3A2 EHV rect arcs across its full 2in length. Im using my original 21FBP22A rare-earth gray screen I installed in place of the 21AXP22 in '64. This is the last and IMHO the best roundy CRT. RCA rates it's ultor at 27.5kv and their data sheet states "Brilliance and definition decrease with decreasing ultor voltage".

[miniman82]

Originally Posted by Tomcomm

an occational 40+kv non loaded run with no 6BK4 reg the little 3A2 EHV rect arcs across its full 2in length.

And what are you hoping to accomplish by doing that?

Im using my original 21FBP22A rare-earth gray screen I installed in place of the 21AXP22 in '64. This is the last and IMHO the best roundy CRT. RCA rates it's ultor at 27.5kv and their data sheet states "Brilliance and definition decrease with decreasing ultor voltage".

Again, you need to stop misquoting the tech sheets. 27.5 is design maximum, not a 'rated value'. Here's a link to the PDF: http://frank.pocnet.net/sheets/049/2/21FBP22.pdf

Any time you operate the tube beyond it's deign center values (found on page 4, which clearly state 20-25kv), you open yourself up to excess x-ray production, and an increased instance of electrical shock or tube destruction from arcing. I caution anyone on these forums from doing anything you're attempting here, I feel it's unsafe on a number of levels as you've already demostrated by destroying a flyback.

[Tomcomm]

Originally Posted by miniman82

And what are you hoping to accomplish by doing that?

.

Since I was replacing the original CT2B FBX circuitry with the entirely different FBX circuitry from a CT almost 10 years newer, I had to know how high the ultor EHV would go if the CRT was at cutoff and the 6BK4 HV reg would suddenly burn out. Surly this makes sense, even to you??

[miniman82]

Originally Posted by Tomcomm

I had to know how high the ultor EHV would go if the CRT was at cutoff and the 6BK4 HV reg would suddenly burn out.

Same thing as any other HV section, voltage goes through the roof.... On my CTC-9, anode voltage shoots up to around 28kv without the 6BK4. But that's common sense, no? Shunt regs are pretty rugged though, why are you worried about burning one out?