[TMC] That pesky PAL 350/500

[Gary Schafer]

Hi Chris,

The screen bypass capacitor should be a large ring that mounts on top of the chassis. It will have finger stock around the inside where the screen ring makes contact. The screen ring is just beloW the plate. 
If you had the tube removed when you tried tried to check the cap via pin 1 it would be disconnected. Look at the bottom of the tube and you will see a small strap from pin 1 to the screen ring. 
Check capacitance from the finger stock to ground.

73 
Gary. K4FMX


Sent from my iPhone

> On Oct 21, 2021, at 10:54 AM, Chris Bolkan <bolkyboats at gmail.com> wrote:
> 
> Hi TMC lovers!
> 
> As you know I'm struggling with my PAL 350. Power output isn't near what it
> should be. The help and comments from the group so far have been wonderful.
> A lot to think about and digest, but so far no ah-ha moment.
> 
> Right now the amp is apart in order to focus on what looks like it could be
> the problem or at least a contributor.  Screen grid voltage is fed through
> inductors to pin 1 on the final sockets (screen grid) and inside the final
> sockets is supposed to be a 1000pf capacitor from pin 1 to ground.
> 
> I'm struggling with this 1000pf capacitor built into the tube socket.  I'm
> not seeing any evidence of it visually or by measuring it. Both sockets
> read exactly 4pf from pin 1 to the case of the socket which is the part of
> the socket that mounts it to the chassis.
> 
> A lot of the socket is translucent plastic and the pins all look exactly
> alike in the plastic. Where is the capacitor hiding? I know these are the
> original sockets. All the screws have the TMC marking dope on them. There
> are no external 1000pf caps on the pins but 1000pf caps are shown on the
> schematic. This amp must have worked as shipped from the factory.
> 
> Has anyone ever taken one of these sockets apart to see how they
> implemented the capacitor?
> 
> I'm so stumped. How did they both fail EXACTLY the same way? Im my world
> that doesn't happen very often.
> 
> Thanks as always!
> 
> Chris
> KI7NXY
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