On 9/16/2010 1:01 AM, Jeff Blaine wrote:
> I picked up an old 76pa which seems to be in otherwise FB condition. 2400v
> idle on the plate cooking away those pipes who have not been used in a couple
> of years prior to some initial power testing tomorrow.
>
> Only strange thing I noticed on the inspection was that every single one of
> the braid connections to the plate cap had delaminated. The braid is
> tarnished so I assume it's silver plated - hard to tell the condition of the
> solder connection otherwise. But the braid was lose enough that the cap
> could be removed from the braid just by bending the braid slightly.
>
> I got to thinking about what could have caused that. Came down to one of
> three possibilities:
>
> 1. The famous alpha plate clip desoldering issue, known world-wide to all
> Alpha owners but not to nubees who expect these things to be soldered in the
> traditional way.
I've owned a 76PA for 8 or 9 years and never had such a problem
> Not to worry though because....
>
> 2. The amp creates a virtual short when keyed down due to it's massive
Massive out of a 76? It is a lot of power out of small tubes though.
> high power output only to have the joint break again with key up. A
> technology known only to Alpha and is top secret such that RF Concepts was
> unable to dig the secret from the ETO data archives. The secret sauce lost
> for all time.
>
> 3. OR - The dogs were whipped mercilessly at one time, so hard that their
> anode temp rose high enough to desolder, AKA SB220 pins can sometimes do.
> Say it's not so!
Then there is the possibility of the fan failing. What do the sockets
look like?
> Hoping some of the learned 76 owners may have some insight.
>
> There was some what appeared to be "melted" gasket material visible on each
> tube.
Gasket material? The only gasket material in mine is the silicone rubber
chimneys and those are not likely to melt.
> Maybe 1/4 in long and a tiny fraction of an inch in height and depth. I
> say melted because it was stuck firmly to the tube and rounded and shiny on
> the exposed surface.
Where on the tube. Anode, base...?
> Interesting because the sealing material will break with age but in that
> case it generally has a rough and "flat" appearance.
I've never had the seals fail on any of the 8873, 8874, 8875, or 8877 tubes.
73 and good luck,
Roger (K8RI)
> 73/jeff/ac0c
> www.ac0c.com
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