"raypsi" wrote in message
...
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:


That resistor is part of the OA3 circuit. All you need is noisy zeners
that can handle the current. You would need 3 watts worth of zeners.
Three 25 volt 1 watt zeners, or five 15 volt 1 watt would give you
more head room. Or 15, 5 volt 1/2 watt zeners, or 1/4 watt. Put 15 SMD
5volt 1/4 watt zeners between the 2 pins on an octal plug, pin 2
connect the anode of the zener string and pin 5 connect the cathode of
the zener string. If you are lucky you can find a 5 watt 75 volt zener

73 OM

de n8zu

GE raypsi,
Wow, what happens when one is asleep! "programmable zener TL431?" One
of the hundreds
of devices that have slipped under my radar!
Is it as noisy in operation as just a few zeners?
My experiences as are no doubt yours too, are that solid state devices
inserted into
vacuum tube perfected circuits just add to the noise generated by computers,
cell phones,
switching power supplies etc.
Do you then need two of those little stinkers (TL431) to come up with
drive for series
FET? (shooting for 75 or so volts, I take it) (or am I too old to understand
solid state?)

TU RAYPSI

W7LTQ