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[AMPS] Suppress the Suppressors

To: <amps@contesting.com>
Subject: [AMPS] Suppress the Suppressors
From: k7fm@teleport.com (Lamb)
Date: Sun, 6 Aug 2000 12:50:37 -0700
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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