[Drake] L7 Bias supply

[Greg Schultz Sr]

Just acquired a real nice L7.  When I powered it up, the HV only got to 200v
and then the breakers popped.  I dismantled the power supply and found one
diode string possibly shorted and one end of the bias dropping 50w resistor
with suspicious arching.

 

I will replace both rectified boards with a new Harbach replacement, but I
still feel that the bias circuit is just a disaster waiting to happen.  So
my question is this  ---  has anyone modified the bias by eliminating the
120v system(and those resistors) and installed a combination zener diode and
bias resistor on the RF deck.  I have read on the internet this is possible
and have some ideas as to how to use the relay to accomplish the necessary
bias in standby and in operation.  Looking for some experience and actual
values of the components.

 

Greg W5RY