[Boatanchors] HF RF Amplifier expert advoce needed

[David Stinson]

I am no expert of anything.   
I keep my "stupid" sign close for easy deployment.   
But I do have a suggestion someone else gave me:  
Check all grounding in the rig.
A lot of the older tube amps ( and just about every other 
boatanchor these days) are starting to experiance 
Hi-Z grounds- screw heads, tube sockets and terminal-strip 
bindings that get oxidized and lose ground.  
I just fixed problems in an aircraft transmitter this evening
that were related to Hi-Z grounds.

The last two amps I worked on 
( Heath SB-220 and Collins 30L-1)
both had very strange problems that were caused by this,
including nasty parasitics in the 30L-1 that were 
very hard on the 811s.  The hardware holding the tube 
sockets were the problem.  Tightened them up to 
clean-up the grounding and the parasitics vanished.
I refurbish an ART-13 once that measured 300-Ohms 
and more right across the places where pieces
of sheet metal were screwed together.
That transmitter was practically open-circuit
from end to end ;-)

Find every screw head that grounds something 
or ties to metal pieces together and give it 
a little eighth-turn tightening.
Any grounding rivets- either solder them or just give them 
a moderate "whack" with a punch.  That usually does it.
Good luck!