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In Reply to: RE: zeners posted by DAK on October 12, 2016 at 17:46:59
I have used both Zeners and glow tubes for the screens on both single ended and differential amps. It works well. It is not a perfect regulator, but it does not need to be. It only needs to be better than the ~18K series resistor you would use from B+ to drop 50V at 2.7mA.
And indeed, you'll probably want a ~100R screen grid stopper anyway which adds 100R of series resistance, reiterating that a few ohms of impedance in the shunt reg is not terrible.
That said, if I were building an amp to be as good as it can be, then the simple Zener shunt is probably inadequate. In that case, I'd include a pass transistor and feed it from a CCS.
I'll add that the zener noise has never really been a problem in this use, but a cap bypass will eliminate it.
Also, I like the series resistor for use on guitar amps for the added distortion.
Follow Ups:
I am almost finished building a SE KT120 amp and since it is "Deluxe" amp with expensive transformers and parts, i wanted to also give the G2 circuit an upgrade if possible. I thought about using the VR tubes but for my chassis , the big transformers have taken up half the space. So, i am pretty much forced to go underneath and compact.
The LR8 circuit with the pass transistor? It's great. I have used it myself. You'll want to make a PCB.
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