I do not wish to impede the quest for knowledge, nor the exercise of clear
thinking - or even unclear thinking, but it seems we have had a never-ending
debate about parasitic suppression.
So, I wish to include my 2 cents worth. I have a number of home built and
commercial amps. i have no parasitic problems with any of them. I have
never destroyed a tube with parasitics - nor by any other means. The only
SB-220 I had to repair was for a friend who turned the bandswitch while
tuning because he was not looking and thought it was the plate tune control.
When I build a cathode driven amp, and before using, I drive it at the
cathode - with a constant output signal generator and no tuned circuit - and
monitor the plate rf voltage with a 500 mhz voltage probe for various
conditions of the output tank circuit - loaded and unloaded. If there are
no hot spots (other than the frequency where the tank circuit is tuned), a
parasitic oscillation cannot be sustained. If there is a hot spot, it can
be addressed by correcting the problem or by constructing a parasitic
suppressor. If you know what the problem is, you do not need a do
everything parasitic suppressor.
Requiring one with special magical qualities seems an admission of defeat in
analyzing the problem.
Before I started a scientific approach, I had an old amp that did all the
bad things. Arcs were everywhere. I tried every parasitic suppressor I
could think of - even Rich's. It still did bad things. Finally, I figured
out that the Pi-L nework was not correct - causing extremely high voltages
to be present no matter what I did. I fixed the problem and the
"parasitics" went away.
73, Colin K7FM
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