Thanks Patrick!
That was my conclusion too. I DO plan on metering the Ik's and wanted to
incorporate
the Rk's for that purpose but wasn't sure why some other designs use other
values.

Thanks


"Patrick Turner" wrote in message
...


wrote:

Hi Group:
I'm working on an output stage of a FIXED BIAS output stage, UL, using
KT88's. According to the data sheet on the KT88, they recommend separate
cathode
resistors. I've seen values in other designs ranging from 0 ohms to 470
ohms! How is
the value derived? I'm using individual bias pots for each tube. The OP
transformer will be
4.3K @ 43% UL taps. I've read through all the books I have and can't find
any discussions on the
subject. I would like to be able to intelligently work this out.
Any help appreciated.

BTW
All of you have a great Christmas!

RonL

Just use 10 ohms, 5 watt, wire wounds.

The 10 ohms is only there to be able to monitor Ik for each output tube.
Fixed bias amps need negligible value cathode resistors to work properly,
and minimise current feedback which is unwanted in output stages.

Patrick Turner.