Thanks to everyone for your responses. Here are the answers to all of the
questions, plus latest results.
The band is 40 meters. There are no padder capacitors in the circuit on
this band. There was a ferrite 'safety' choke across the output. It was
getting warm, so I replaced it will the usual 3 mH (300 mA?) pie-wound
type. I will revisit this because I want a choke that will blow the PS
breaker if the blocking cap shorts and I don't know if this one will.
I think this choke was part of the problem.
To answer G3RZP, the plate choke is an Ameritron 225 uh choke. The bypass
is an 0.01 disc in parallel with an 0.001 at the bottom of the choke. Then
there is a 25 ohm 50w glitch resistor, which is bypassed at the cold end
by a second 0.01. The HV coax is also bypassed by a third 0.01 where it
exits the RF deck.
The plate, screen and bias voltages are solid. What I am seeing now is
that the screen current drops while I hold the key down for 10 seconds,
from around 25 to 13 mA. But it more or less stays there and the amp
doesn't fault.
Tuning is VERY touchy. You really have to have the loading right or the
screen current is excessive in either direction.
Consider using less variable Load C on the higher bands plus a vernier as
most commercial amps use.
Carl
KM1H
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