[Amps] Questions on hot switching 2700V B+ to a 3CX800 amp.

Mike Krzystyniak K9MK k9mk at flash.net
Sat Aug 12 12:07:53 EDT 2006


Greetings all,

    I own several Henry VHF/UHF amplifiers that use 3CX800 finals.

    I have long been disappointed on the noise and mechanical vibration
noises created by these puppies.  They also get quite warm just sitting
there idling, I think mainly because of the heavy bleeder resistors across
the filter caps.  Not until this recent Texas heat wave has the heat
generated by idling the amps caused an ambient temperature build up in the
shack been an issue.  The obvious solution might be an exhaust fan or maybe
better ventilation which leads to installing another 3 tons of HVAC to keep
the shack cool. Yup, that would nail it.  But financially not very
attractive.

    I was wondering if there are any issues with warming up a 3CX800 without
B+ and then using Solid State relays (or maybe some other scheme) assert B+
only when PTT is keyed.  Implementation options seem limited and I'm far
from an expert in these matters so I was wondering if there could be some
issues with the tube being damaged, or possibly surge damage issues in the
power supply.

    Certainly there has to be some other novel ways to address these issues.
What say Ye experts?

    Thanks & 73's  Mike  K9MK/5








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