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Regulated Variable High Voltage Power Supply - Stereo Amp
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Author:  NW2K [ 14 Nov 2020, 07:49 ]
Post subject:  Regulated Variable High Voltage Power Supply - Stereo Amp

I'm building a couple of variable regulated HV power supplies for a stereo amplifier, which use the Antique Wireless Association's printed circuit board. The circuit uses a TIP50 pass transistor on a PCB-mounted heat sink.

With natural convection at room temperature, the heat sink works fine with a dissipation of 10-12 watts or perhaps higher. I have not had any TIP50 failures and I've used the supply extensively between 150 - 330 VDC, staying within the 10-12 watt CCS dissipation. I've also used it down to 90V with good results. I can say that I exceeded that dissipation significantly, intermittently.

I'm considering mounting the pass transistor remote from the AWA PCB on another heat sink. Before doing that, I wondered if there were any HV alternatives to the TIP50.

Someone mentioned the MJW18020 and it looks like a good candidate. Has anyone here used it in a piece of audio gear?

To get a sense of scale, here is what it looks like in a 6SN7 stereo preamp prototype, a light-duty application. It works at B+ 320V. Thank you.

Attachment:
6SN7 Stereo Preamp with Antique Wireless Association High Voltage Power Supply PCB Small.JPG

Author:  M. Gregg [ 14 Nov 2020, 08:25 ]
Post subject:  Re: Regulated Variable High Voltage Power Supply - Stereo Am

Quote:
I'm building a couple of variable regulated HV power supplies for a stereo amplifier, which use the Antique Wireless Association's printed circuit board. The circuit uses a TIP50 pass transistor on a PCB-mounted heat sink.


I have never used the PCB you talk about.
My experience with HV power regulators is they are OK until a short occurs and blows the pass device apart.

From a dissipation point of view you can put a "burden resistor" in front of the regulator and calculate the voltage drop across it so the heat dissipation is shared between the pass transistor and the burden resistor in series with the regulator. As long as the voltage drop across the resistor isn't to great you won't get SAG. You can calculate the drop so you have enough head room for good regulation.

You could use a MAIDA style regulator with a FET and LM317 as another option. Apparently the pass device can have an effect on the HF response of the amp but its down to your own ideas really.
The burden resistor can be a HV wire wound type.

Regards
M. Gregg

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