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Re: [Amps] Replacement of plate caps on glass tubes

To: Amps@contesting.com
Subject: Re: [Amps] Replacement of plate caps on glass tubes
From: Bob Bruno - K2KI <k2ki@starc.org>
Reply-to: k2ki@starc.org
Date: Thu, 10 Apr 2008 11:12:53 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Hi Mike,

Yes, they can in most cases. I have successfully done it on many tubes.

Get some Furnace cement and use that to bond the cap to the tube..

What I do is make the hole in the top of the cap slightly larger than 
the wire. Then put some lead dressing, shrink, whatever through the hole 
and extend it past the bottom of the cap. Then I fill the cap with a 
generous amount of Furnace cement and then slip the cap with the 
dressing over the lead and slide it onto the tube. Then I carefully 
remove the dressing thus exposing the clean wire. I can then solder the 
lead to the tube. It works better if the dressing or whatever material 
you use is a snug fit to the hole. This helps prevent the cement from 
coming out with the dressing as you pull it out.

If you need to extend the lead a bit to make it clearly out of the hole, 
make sure your splice and solder the new wire to the old really well! 
You don't want the thing to open up or become resistive inside the cap 
from tube heating!

Also, a little amount of flux added to the top of the cap might help 
make the bonding process a little better.

As I stated earlier, it can be done in most cases. Your mileage may vary.

I'm sure there are many other ways to do this. and I look forward to 
hearing them.

Hope this helps...

73, cul...
Bob de k2ki

K6QD wrote:
> I have some old glass tubes where the plate cap bond to the glass envelope 
> has become loose; i.e. the cap is being held on by the soldered wire going 
> through the glass envelope to the internal plate.  The solder joint from the 
> wire connection to the plate cap is intact and the tubes are good, but the 
> bond to the glass has failed over time.  Can the caps be unsoldered, 
> re-bonded and re-soldered?
> Thanks for any help.  
> de Mike, K6QD
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