Jon wrote:
> Rich, you've never ever responded and tried to defend your suppressors
when I tell the story of how I thermally burned them up in my amp on 10M.
Just to throw in an empirical observation, I burned up the stock suppressors
on my "new" LK550 while tuning up on 10M at full power and trying to adjust
the ALO trip circuit. The procedure is to throw the loading off, let the
grid current soar, then quickly adjust a pot to make the ALO trip.
Unfortunately, I wasn't watching the plate current closely enough. Smoke
started billowing off of one of the parasitic suppressor resistors.
Subsequently, the amp tuned fine on the lower bands, but when tuned on 10M
beautiful chemical sparks danced all over the suppressor coils (kinda like
the Bride of Frankenstein.) Inspection revealed two resistors had split in
half, exposing the carbon (which was causing the sparks), and the resistance
of the third was about double its nominal value. IMHO, high levels of plate
current on 10M (inefficient due to poor tank circuit design) heated the
suppressor coils, cooking the resistors inside them. Both Tom and Jon have
indicated that some RF goes through the resistors at 10M, contributing to
the overheating. I'll bet this is not uncommon on 3-500Z amps, and I don't
think parasitics have anything to do with it.
Most amps I've seen have the resistors inside the coils. A number of
aftermarket replacements have the resistors outside the coils. I'm curious
about the origin of the design technique that places the resistors inside
the coils. Is there an electrical reason for this or was it just to save
space?
BTW, until I could get my hands on some aftermarket suppressors with
resistors external to the coils, I just replaced the resistors. Now I tune
up on 10M with a 75 WPM stream of dits at 1:3 duty cycle. I got that idea
from Rich.
73, Dick, WC1M
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