I also use furnace cement but do it in a slightly different way.
Clean out as much of the original cement as possible, rough up any smooth
areas.
Thin the cement with water so it is a little thicker than the consistency of
regular cement.
Tin the plate lead and put a thin film of flux on it..
Fill the upside down cap with cement.
Install tube, hold cap on with fingers, turn upright and place in a socket.
Hold down cap while flowing solder on the lead depression. Try not to burn
fingers!
Wipe or brush off any visible cement with water. You can also outline the
cap with a marker pen and lightly oil or Vaseline the surrounding glass.
Place tube in the toaster oven, in sunlight, or whatever to conform to
curing process detailed on container. Do not install connector until fully
cured. Some circuits may allow you to install tube and operate with filament
only.
For loose tube bases use another furnace product, refractory cement, aka
water glass.
If you live in an area without home furnaces go to a heating supply
contractor as they are used by commercial/ndustrial sites.
DO NOT use super glue on tube bases, it has been known to fracture tubes as
it ages.
Carl
KM1H
----- Original Message -----
From: "Bob Bruno - K2KI" <k2ki@starc.org>
To: <Amps@contesting.com>
Sent: Thursday, April 10, 2008 11:12 AM
Subject: Re: [Amps] Replacement of plate caps on glass tubes
> 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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>>
>>
>>
>>
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