> Of course, with age things can change and the stability margin of the amp
> can shift. It is highly unlikely though that in an HF amplifier much could
> change and go wrong with age. Tubes end up putting out LESS gain as they
> get older not more (more would hurt stability) and most of the other
> components really don't change much. The only thing that could really
> change would be that the suppressor resistors end up dying from being
> constantly heated. Then you CAN have an oscillatory situation.
When the manufacturers started producing suppressors made of one or
two 2 watt carbon resistors and #12 wire for legal-limit amplifiers coincided
with increased use of 10 meters due to the sunspot peak in the 1980's,
it laid out the prelude to disaster that followed. IMHO, a suppressor with less
than a 6 watt rating belongs in an exciter or driver stage. I suggest that 90%
of the modern-day suppressors are under-engineered by at least 50%. Nichrome
retrofit kits are not magic; they are just more robust than what they replace,
in
most cases. In the case of a 4-1000A, a suppressor needs to be made of
nichrome or copper strap and at least a 12 watt resistor if you expect it to
last any length of time at all. There is a finite limit to how small you can
make
a 1500 watt amp, and I think that limit was exceeded several years ago.
(((73)))
Phil, K5PC
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