On 6/23/2016 4:41 PM, Floyd Sense wrote:
I recently acquired an early Centurion (serial 10A10221) from an SK's
estate. The resting plate current, PTT not keyed, is around 100 ma and
the 3-500ZGs have a nice orange plate glow. I had read in the archives
that later changes resulted in a much lower resting plate current and
set out to see what the current state of circuits is in this amp. (
Yes, I know that level of plate current is OK, but it generates
considerable heat on the desk that I don't need.)
The amp has obviously been updated at some point as the Filament-AC
board has the new bias circuitry and the QSK board is revision C. The
Filament-AC board circuit as shown in the 10/94 rev C diagram agrees
with the schematic. So, I'm guessing that I might have all the latest
changes in regards to bias. The question is: Is the observed 100 ma
resting plate current what others are seeing in the Centurion with the
later bias changes? If that level is normal, I was thinking about
maybe using the Ameritron ESB-1H board which would reduce the resting
current to just about nothing with no excitation. Any thoughts?
Tentec has not responded to an email on the subject.
73, Floyd - K8AC
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As I recall, the resting plate current should be close to zero. On my
Filament-AC board, I had to replace the transistor two different times;
for whatever reason, they were a bit notorious for failing. Before you
do anything else, take a close look at that transistor, Q1, 2N3055.
Also, according to the manual, the QSK board (81542) can cause a similar
problem.
LETHAL voltages inside, be careful!!!
73,
Carter K8VT
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