On May 30, 7:20*pm, "coffelt2" wrote:
"JIMMIE" wrote in message

...

I want to replace the vr 0A3 tube used in the bias circuit of a 6146B
amp with a 75V zener string. Can I just directly replace the tube with
the diodes or *will I need to make other modifications to the circuit?

Jimmie

Don't know if I read all the responses, but I hope someone explained the
need to provide a series current limiting resistor in the zener string.
Something that would keep the no load current up near the top of the zener's
operating range would be good.

Old Chief Lynn, W7LTQ

Hey OM:
I take a DC supply from the filament voltage and use that to power a
programmable zener TL431. and use a FET to replace the OA3 driven by
the TL431.

I've replaced OA2's this way, all it takes is three 1/2 watt resistors
to set the voltage.

73 OM

de n8zu