Rob Atkinson, K5UJ wrote:
I'm working from memory--I'm sure someone else knows exactly what this
is or you can find it in the reflector archive--the Centurion originally
was biased so the 3-500s were operating @ around one or two hundred
mills when not transmitting. the mod shut them down completely between
key closure. Do I have this right? someone help me out here--
I guess it depends on the vintage. Mine came from the factory with the
board already installed. It was a "Revision B" board. Very early
Centurions may not have had it at all. The rev B board blew up on me a
couple of times and I got tired of fixing it so I finally bought a new
Rev C board from TT and it has worked flawlessly for the last several years.
The only other mod I put in was a wire wound resistor to lower the
filament voltage. It is probably a quirk with my filament transformer,
but the filament voltage was quite high even with "nominal" primary
voltage. As the cost of 3-500s is steadily climbing, the point of the
exercise was to extend tube life. I guess the real fix would have been
to remove a turn or two off the secondary of the fil xfmr, but I wasn't
retired then and didn't have time to do it that way...
73/Carter/K8VT
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