That sounds totally wrong to me. The rf needs to go onto the
common point of the cathode and filament (or heater as I prefer to
call it where there's a separate cathode).
As long as the heater supply has a decent rf choke close to the
tube I think a capacitor across the two connections isn't vital,
but I can't see it does ay harm either.
Inside, the GS35 is a big planar triode. The cathode is a slightly
domed disc about 1" diameter and I assume the heater is spiral
wound against the underside so there's likely to be enough
capacitance between them to matter at VHF - but I doubt it's the
quality of capacitor you'd want to use to couple rf onto the cathode.
Steve
Just looking for a reality check here. I am trying to get an
amp running. It was not built by me and had apparently been
sitting for quite a while.
Everything seemed to be working but the input SWR wouldn't tune
below 4:1 with about 25W drive. I understand it will change
some at full power but I don't think this circuit is working as
desired and am reluctant to put my SS driver PA into it.
I pulled the bottom cover to look at the input circuit. It's
the usual T with two coils (not the usual dimensions) and shunt
capacitor between them. BUT, it is connected to the bottom
connection of the tube. I think that is the filament connection
that is NOT common to the cathode. There is NOT a capacitor
across the two filament/cathode connections. All of the
circuits I could find online this afternoon show the RF input
to the next ring up on the tube (filament/cathode common). Some
show a capacitor across the filament connections, some don't.
Comments?
I am inclined to rip this out and rebuild. The 10 AWG hard
silver plated wire the coils are made from makes it impossible
to spread or compress turns to experiment with the match.
Thanks, Paul
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|