Simplistic MosFET HV Shunt Regs

diyAudio Chief Moderator
Joined 2002
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Depends on what ailment that CCS was mainly fixing in a design. If its basically for PSRR and not for problems with stability of bias or to absolutely achieve a certain voltage gain, then a cleaner and already CCS blocked B+ can be a good reason to re-evaluate a proper value plate resistor in its place. That will change the load line from horizontal to slant and remove any intrinsic hiss from that CCS element if it was detectable. It will come out different. In other words, experiment and evaluate.
 
Would it make sense to forgo this plate ccs and connect the output of the sshv2 directly to the tube plate?
If you put the question this way - no. After the CCS in SSHV there is a shunt. In most cases CCS in the plate is the load for the stage (as the biggest impedance). The shunt from the SSHV would effectively dump all the signal from the plate to the ground.
 
Thanks! This makes a lot of sense. I like the idea of trying a plate resistor.

One more question, can you give a guideline of minimum capacitance needed before the regulator? I will have a CLC in a separate box with something like 10uF 15H 47uF. I simply don't have room in the amp chassis for much capacitance. I was wondering if I could get away with say a small series resistor in the second chassis and then 1uF right near the regulator input (another RC essentially)? I realize you have advocated many times to avoid this configuration but in this case it will be my best option, if I can keep the regulator performance up.
 
diyAudio Chief Moderator
Joined 2002
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1uF wouldn't be effective at ripple frequencies unless the R would be impractically big value eating out too much voltage. But it would still be a welcome cell for rectification's EMI attenuation and umbilical decouple. Practically try your prefilter config to measure no more than 500mV RMS ripple at the reg's input. Can't you use say 47uF electrolytic instead after some small R there? Still not that bulky.
 
luvdunhill: Why not add a 220uF electrolytic after the choke? that would improve things alot. I don't know why so many people here are afraid of electrolytics in PSU. At least to my findings there isn't pretty much any difference at all sound wise- if bypassing them with film caps.
And i also take the first 10uF that you have a tube rectifier? otherwise there is no need to use such small value.