I'm retrofitting an Alpha 76A with 3cx800A7's. Eimac states
unequivocally, that "...heater voltage be applied for a minimum of 3
minutes before anode voltage and rf drive are applied...". Rather than
completely reconfigure the Alpha start up circuitry with their step
start and 1 minute delay sequence, I've decided to disregard that delay
function and add a 3 minute solid state delay relay and to switch in one
leg of HV from the plate transformer. Here's the questions: After the
delay,
1. Is it more prudent to switch in one of the HV AC legs before
the full wave bridge rectifiers or to switch in the B-?
2. Is a completely enclosed mercury displacement* SPST relay a
better choice than a standard P&B DPDT
relay reconfigured for SPST to accomplish the task?
* Can anyone familiar with the relative merits of a mercury
displacement relay explain its design?
Any guidance would be greatly appreciated. Ron W2CQM/3
PS: If I could ever locate the elusive SPST vacuum relay I have
somewhere in inventory, the questions would be academic!
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