I'm building a high voltage power supply for a tube amplifier preamp and I need some advice.

I need a power supply with a shunt regulator that is rock solid stable and dead quiet and outputs 600v with a maximum of 100ma current draw that will be adjustable down to 2ma. The next stage of the design requires a stable voltage and the stage will amplify any noise so I need a good design.

This is what I have right now enter image description here

I don't trust the stability or noise of that series regulator design. After building it in real life it seems to droop a few volts and I'm not sure what to think about the noise.

The resistor in the RC filter is underlined with question marks because I don't know the shunt design or overhead voltage that I will need for it.

Does anyone have any advice on a quality shunt regulator with as low noise as possible?

  • \$\begingroup\$ What parts did you use for Q1, Q4 and D6? What measurements have you made? \$\endgroup\$
    – Steve G
    Commented Feb 7, 2016 at 19:50
  • \$\begingroup\$ IRF840 for Q1 and Q4. D6 was mouser.com/ProductDetail/Vishay-Semiconductors/BZX85B100-TAP/… 1.3w 100v zener in series with a 56v equivalent for a 200v output power supply. It dropped several volts under load. I need a shunt regulator that won't drop anything. \$\endgroup\$
    – coinmaster
    Commented Feb 7, 2016 at 19:52
  • 2
    \$\begingroup\$ That's not a shunt regulator at all- it's a ~475V series regulator (with missing gate protection and dubious stability). What do you actually need? \$\endgroup\$ Commented Feb 7, 2016 at 19:59
  • \$\begingroup\$ Yeah sorry, not sure why I said shunt regulator for the above circuit. Now that you mention it, I'm not sure what it is that I need. Shunt regulators draw maximum current from the power supply at all times right? I've heard shunt has better peformance but then again, maximum current across the RC filter would require a whopping power rating on the resistor. \$\endgroup\$
    – coinmaster
    Commented Feb 7, 2016 at 20:22
  • 1
    \$\begingroup\$ Is this preamp for an antenna (if so, what band), or for a microphone? My 'gut' response would be to build/get a PWM SMPS to boost up to ~610V; make sure it operates several octaves outside your frequency band of interest; then add low/high-pass filters to block SMPS noise on Vout & short the noise to GND (i.e. at least 2nd order). \$\endgroup\$ Commented Feb 7, 2016 at 22:15

1 Answer 1


Yeah I just realized a shunt regulator would require far too much constant power draw through the power supply resistors at these voltages. I think I need to go with a series regulator. One that happens to be extremely quite and stable. I would prefer a shunt but I don't think it's an option here.

  • \$\begingroup\$ Valve stuff generally draws a more constant current than solid state equipment .This looks like high end audio so it will off course be class A so the average current is constant .This means that load regulation in not important .Your proposed regulator is only for line regulation .You may not need it and its noise .Maybe you could spend the money on more power supply filter caps \$\endgroup\$
    – Autistic
    Commented Feb 8, 2016 at 6:09
  • \$\begingroup\$ The maximum current draw will be 100ma, far below the maximum draw of the power supply. The anti-triode CVS gyrator load of the input tubes requires dead stable input voltage. This isn't for an output stage it's for the preamp/amplification stage. As far as I know a shunt regulator requires full current draw across its resistor which would require a over 100w of power dissipation. A series regulator only draws what the load draws right? \$\endgroup\$
    – coinmaster
    Commented Feb 8, 2016 at 10:18
  • \$\begingroup\$ OK you can keep your reg and you can post filter if there are still noise concerns .Now be careful about your Powermosfet in linear mode ,it is not as robust as you think. \$\endgroup\$
    – Autistic
    Commented Feb 8, 2016 at 10:35
  • \$\begingroup\$ Well I don't intend to be using that regulator, it's not stable. Which is why I made the thread :P I need advice on design. \$\endgroup\$
    – coinmaster
    Commented Feb 8, 2016 at 11:07
  • \$\begingroup\$ Try to use just one fet and a stable zener that is about 3V more than you need .You may need to make the stable zener out of lots of parts .If you do this you wont have any feedback loop stability problems. \$\endgroup\$
    – Autistic
    Commented Feb 8, 2016 at 21:41

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