• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Solid State Regulator for tube amp

Hi Folks,

Let me introduce. I'm from Brazil and i'm here in USA working as Electronic Engineer as i've graduated in Brazil.
I had a small company in Brazil which we use to manufacture old push pull amplifiers AB class for cars. In Brazil they call this amplifiers boosters. For so many reason in the economy i've decided to quit the company and move to USA.
I've never had built a tube amplifier, but i've decided to buy a DYNACO ST-35 to start. As a lover audiophile the sound was amazing. I really liked, but i have some problems and i would like to fix it.
First the power supply is keeping the voltage higher than it could be because i use another kind of transformer wich deliver 394 volts for the EL-84 where it should have maximum 300V right?
So i would like to build a High voltage solid state regulator for that using some mosfet. Is anybody have some idea. I know that it's hard to find some circuit to start because nobody seems to want a solid state to regulate high voltage.

Thanks guys,

Luiz Nickel
One MOSFET, for example IRF740, couple of SG-4S gas discharge tubes in series, 10KOhm / 5W resistor, and one 12V Zener to protect gate. Nothing more is needed. Except may be one 22 Ohm / 5W resistor to protect MOSFET against sudden surge current.
I.e. parametric stabilizer + source follower.

More than adequate regulation for your particular case, also nice purple glow.

I've build that one and I like it very much. I use it to power a 300B.
Especially the slow-startup is very nice, it takes about 50s to get to 500V.
Drawbacks are: You need a clean voltage to power the regulator and the amp makes some funny noises when you turn it off.

You can read about it here:

High Voltage supply
Solid State High Voltage Regulator

Hi Guys,

Let me explain what is going one...
I don't want to use any tube to regulate the voltage.
I don't agree with the DYNACO ST-35 MANUAL where they have the tube voltage measures for the EL-84's around 360 Volts on anode and 13 on cathode. With that the tube is going to be with 347 V where should be maximum 300 V.
I'm wrong with that ?
Actually I know that my problem is different than this. I want to build a solid state regulator with 394 VDC IN and 300 V out and at least 300mA. I mean around 9W.
I liked the idea to use the IRF740, but without the tubes.
I saw that i could use the LM317 too. Does anybody have another ideia ?
I would like to put my amp pictures here, so everybody could see my baby, but my pictures are around 500Kbytes each one and i don't know how to reduce the size. How can i get that ?


Re: Solid State High Voltage Regulator

NBBN_amplifiers said:

I liked the idea to use the IRF740, but without the tubes.

Zeners don't glow, the rest will be the same... I've found such a regulation, I mean a parametric stabilizer with a source follower, more than adequate. I use such approach to regulate G2 voltages for output tubes and B+ for preamp stages. Better regulation improves nothing sonically.

Edit: however, some 20 uF cap to shunt Zener noises out is desired.

I saw you said "I want to build"..... However, here are some links to solid state regulated high voltage PSU´s. If you do not want to buy them assembled I hope they might be of some kind of inspiration for you.




Kinds regards

Voltage Regulator

Ok Guys,

It's a pleasure to participate of this most valuable group.
I'm going to build a regulator using the IRF740 + zeners + resistors ...
Definetly will be enouth with a good head sink.
I'm going to put the circuit when i have time here based on

I still want to put my amp pictures here can anybody help me with ? The pictures are around 500kbytes...
How can i reduce this size ? Is that any trick ?