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  #46  
Old 11-13-2013, 09:26 AM
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I'm not a good enough scientist to guess whether dripping is a possibility, or whether the rusting resulted from moisture in the ambient atmosphere. I could probably build a box with sturdy supports to hold it face up, if that seems important.

Whatever I do will need to be fairly low-tech. For instance, I could store it in a sealed plastic bag with some dessicant gel.

Phil Nelson
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  #47  
Old 11-13-2013, 10:10 AM
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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.
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  #48  
Old 11-14-2013, 11:50 PM
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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.
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  #49  
Old 11-16-2013, 10:47 AM
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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.

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  #50  
Old 11-22-2013, 12:35 AM
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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!

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  #51  
Old 11-22-2013, 01:21 AM
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Last year there were at least two 21FBP CRTs for sale at the ETF so chances of finding one are good. Nick (AKA miniman) told me when I bought my set from him that on another CTC-4 he has for a time he had a glass tube in it and there was a scope HV lead that either worked straight up or at least had the correct plug to plug into the HV cage. I took the lazy path and used a salvaged BPC TV HV wire and carefully stripped a long section on the end of the wire, folded and soldered it until it would mesh with the female HV connector on the HV cage. and I sandwiched some thick plastic bags between the yoke and the HV connection on the CRT and the yoke.
It ain't the prettiest metal to glass CRT conversion, but it DOES work just fine.

You can do the metal to glass CRT conversion. Others have made it work in the past so there is no reason that you can't.
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  #52  
Old 11-22-2013, 09:51 AM
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Tektronix scopes have the tower connection you need, but the glass tube anode does foul the yoke support causing arcing. You can try to insulate it somehow, cut the support to gain some clearance, or rig up your own crt mounting system.
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  #53  
Old 11-22-2013, 10:49 AM
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Speaking of arcing, in the HV cage the 22-ohm resistor was burned and broken and the hood for the 6BK4A regulator tube was nibbled away, with evidence there had been arcing through the hood to the inside of the cage. I scrubbed the hood inside and out when I replaced the resistor and the electrolytics. Let's hope that puts an end to the fireworks.

Phil Nelson

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  #54  
Old 11-25-2013, 07:58 PM
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With a couple of new tubes, now I have great audio and decent sweep waveforms, plus a reasonable stair-step waveform at the video amp when I supply a color bar signal. Here's one of the horizontal waveforms:



Too bad my CRT is a dud!

Phil Nelson
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  #55  
Old 11-26-2013, 06:59 PM
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Signs of life...I bet it makes high voltage, try it out.
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  #56  
Old 11-26-2013, 10:20 PM
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Yah, it makes HV. This looks like about 19.5 KV. At the moment I'm running it from an Isotap at 110 VAC line voltage.



Had to scrounge for something to defeat the HV interlock. This cap from an old Disneyland pen did the trick!



This chassis seems very stable. I feel like I could be watching a movie tonight if I had a usable CRT. There are other things I can do in the meantime, but none of them half as fun as seeing that first image on the screen.

Phil Nelson
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  #57  
Old 11-27-2013, 10:54 AM
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It really needs to be run at 117 VAC, that will stiffen it up quite a bit. Mine had the seleniums replaced with silicon diodes and a dropping resistor, so it's probably a little stronger than yours in HV production. I have mine set to around 24kv on the anode, but it will go much higher if you let it. Have you gone through the horizontal circuit setup procedure yet?
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  #58  
Old 11-27-2013, 11:40 AM
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I haven't done anything besides power it up at reduced voltage and take a few readings while watching out for smoke. After the holiday, I should have time to replace the seleniums and start on all that other good stuff.

Phil Nelson
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  #59  
Old 02-20-2014, 01:07 PM
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Thanks to the generosity of another VK member, I have a 21FJP22A with good emission. It arrived yesterday, in my homebrew CRT box that I shipped to him empty. He popped in the CRT and sent it back, and it arrived here in fine shape.



I haven't tried anything on for size yet, since the cabinet is completely disassembled, but I guess some people would cut a notch out of this retaining ring to avoid fouling the 2nd anode lead on the new CRT.



It may be a while before I get to try out this CRT with the chassis. During our remodel, my workshop is packed into 100 boxes and temporarily piled in our new garage, which doesn't have power yet. Our living quarters are so crammed with overflow that I had to unpack the CRT in our front entry -- and then clear away all the mess before dinner guests arrived.

Phil Nelson
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  #60  
Old 02-20-2014, 03:12 PM
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I previously posted this RCA production line photo to ETF. For those that have not seen them I'm posting them here as well. Phil, perhaps one of these is your CTC-4 "Director".

-Steve D.
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