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  #46  
Old 09-13-2008, 10:06 PM
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Thanks for the advice. I popped for the vac-seal. Scotty looked at the tube and thinks the face and neck seals look OK - he thinks it most likely that the leak was at the metal evacuation pinch off. Of course, there is no guarantee, which I fully understand, but I am willing to risk the cash based on a reasoned examination. If it doesn't work, it's back to looking for a dud under vacuum.
I think everyone involved has their fingers crossed!
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  #47  
Old 09-13-2008, 11:54 PM
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We who have attempted 15GP22 rebuilds have our fingers crossed for you!
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  #48  
Old 09-14-2008, 07:22 AM
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[1] Fingers are crossed...

[2] Yes, there's something unseemly about a stream of water under pressure cleaning a valued chassis, but there have been no negatives for me so far, and I use it just as a first step before the hands-on cleaning and polishing.

Drying the wet chassis is important and I always use some combination of:

*wiping it with a cloth

*making sure the day is hot, sunny, and dry to 'bake' out the moisture (turning occasionally to get all sides and the bottom)

*and using a leaf blower to remove standing water and 'blow dry' the beast (this is the best way to remove moisture from hard-to-reach cracks and crevices).

Pete
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  #49  
Old 09-14-2008, 09:23 AM
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I too use the hot water/pressure approach to cleaning a chassis. The only thing to be careful of is cardboard and paper. I've found that if the chassis is dried thoroughly, parts won't be damaged.
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  #50  
Old 09-14-2008, 01:27 PM
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So for the cardboard and paper do you just wrap them up the best you can, or just avoid them? My 63 Zenith is pretty dirty looking, lots of dust. My 53 B&W Zenith is alot cleaner.
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  #51  
Old 09-14-2008, 02:54 PM
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Quote:
Originally Posted by John Folsom View Post
We who have attempted 15GP22 rebuilds have our fingers crossed for you!
Scotty showed my some 15GP22s with obvious leak points - they look like filaments of air crossing the seal surface from outside to inside when you look from the front. Some tubes had a lot of them. No such obvious defects on the 21AX. He also tried a spark coil to see if he could get any sparking through the glass.
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  #52  
Old 09-14-2008, 04:23 PM
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Testing tubes in the CTC-5, using a Realistic model 108.

I'm getting suspicious results on the 12AT7 color demods. The tester table says to use a quite low setting (4) on the "D" dial, which means a low reading for a given amount of current; that is, the tester expects a lot out of these tubes. Anyway, both demods read really low unless I increase the setting (I tried this because one of the types that could substitute requires a higher setting). Also, the reading jumps to a peak value when the button is pushed and them fades to lower values (easier to see if the "D" knob is cranked up).

Any ideas? Something wrong with the tester? A mistake in the settings table? I have tested about half the tubes and the 12AT7s are the first ones to behave this way. Found one dead 5U4 rectifier, otherwise the other tubes behave reasonably.
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  #53  
Old 09-15-2008, 09:19 PM
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well, I found a couple of 12AT7's I bought last year for another project, and they test out OK! So, both in the CTC-5 were fried - must have made the color a little weak - but with the CRT dead I suppose it was dark too. So much for that recollection of it "working the last time it was turned on"
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  #54  
Old 09-16-2008, 01:51 AM
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Quote:
Originally Posted by old_tv_nut View Post
Testing tubes in the CTC-5, using a Realistic model 108.
I am amazed to see that Radio Shack once made an item like that. Times sure have changed, so much. Even as of the mid-70's when I started going to RS often and bought plenty of their kits and parts, I don't think they had anything close to a tube tester for sale.
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  #55  
Old 09-18-2008, 11:20 AM
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Well, bad news on the rebuild of the aired 21AXP22A. Despite liberal use of Vac-Seal, and Scotty's optimistic examination of the aired tube, it did not achieve a good vacuum. Scotty reports that the gun looked OK after evacuation/baking (indicating not much air if any), but the getter flash looked abnormal, and now the tube shows internal blue glow under test. So, there's some unidentified small leak.

I'll be driving out to see it and retrieve it on Sunday. At this point it's not worth a second try without knowing where the leak is and whether it could be sealed for sure.
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  #56  
Old 09-18-2008, 01:49 PM
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Sorry things are not going well, the set is worth the effort though. Hopefully you guys can figure it out or find a good AXP somewhere.
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  #57  
Old 09-18-2008, 03:31 PM
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Oh dear. That IS bad news. probably does not bode well for the leaker 15GP22s, but then again, who knows? We still intend to attempt a leaker 15G, possibly on our next trip to Hawkeye.
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  #58  
Old 09-18-2008, 08:49 PM
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Quote:
Originally Posted by old_tv_nut View Post
At this point it's not worth a second try without knowing where the leak is and whether it could be sealed for sure.
On the bright side, let's hope there's a possibility of gaining valuable insight as to how early roundies leak.

Pete
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  #59  
Old 09-18-2008, 11:18 PM
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To follow up on Petes suggestion, Wayne, you should ask Scotty if he can use his sparker (high voltage AC power supply) in an attempt to isolate where the leak is in the 21AXP22. Maybe this could lead to some insights.
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  #60  
Old 09-19-2008, 08:17 PM
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Quote:
Originally Posted by John Folsom View Post
To follow up on Petes suggestion, Wayne, you should ask Scotty if he can use his sparker (high voltage AC power supply) in an attempt to isolate where the leak is in the 21AXP22. Maybe this could lead to some insights.
He has tried it, but we will try again. I'm driving out tomorrow and will see Scotty on Sunday, so I'll have an update hext week.
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