One other thing to be careful about in these designs is the minimum current- below a certain threshold (you'll have to check the datasheet, my memory says "5 mA"), the 317 won't regulate. At low voltages, this isn't generally a problem, the feedback resistor is set to 120R to guarantee 10mA. At high voltages, that means a lot of dissipation in the set resistor. Once your tube warms up, that's usually OK, but without some minimum, the output voltage will rise to something near the input. That may or may not be a problem for you, but you should be aware of it.
George's point about current through pot wipers is correct, which is why I did the little divider trick in the RLD regulator. It limits adjustment range, but in a screen reg application, that's OK- you might not even want adjustability in the first place.
George's point about current through pot wipers is correct, which is why I did the little divider trick in the RLD regulator. It limits adjustment range, but in a screen reg application, that's OK- you might not even want adjustability in the first place.
I guess regulated g2 is good for linearity, but having fixed biaszon both grid1 and screen grid can potentially promote thermal runaway. Also for amps where the plate swings below the screen it may be a bit hard on the screen. Stii, I need to try it since you all say it gives the best results, or maybe I'll stick to triodes.
There was an amp in Sound Practices that had a regulated screen supply... I think it was using a 6BQ5 as the pass element, regulating paralleled SE outputs. J.C Morrison designed it. Fascinating circuit, I was really tempted to build it. I was a college student at the time and it needed a monster output transformer...
I will see if I can dig up any info on it.
I will see if I can dig up any info on it.
The amp you are looking for is in Sound Practices issue #14 page 12. It is called the Blackie Box. It used a 5842 to drive two paralleled 6L6G's. A 6BQ5 is used as the pass element for the output screens but it doesn't appear to be a regulator since it has no reference voltage (zener or gas tube).
The material is copyrighted So I can't post it here. It is on the Sound Practices archive CD which may still be sold. It might be found out there somewhere on the web.
I have seen several screen regulators that used tubes as the pass element. In fact the zener - resistor - mosfet circuit works with tubes since the mosfet is wired as a source follower. A tube can be used in cathode follower configuration. Tubes that work good for cathode followers can be used if the current rating is OK. 7233, 6S4, 12B4, triode wired 6CW5, and triode wired sweep tubes are common.
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