[serengetiplains]

Paul, are you able to make a power supply to operate at 650VDC?  I need a supply to power an EL34 amplifier.  The amp runs two tubes per channel for a balanced-out headphone amplifier. 

Will two supplies, one for each channel, allow better noise reduction on the output?  Or do you think running one supply per tube is best?

Cheers!

[Paul Hynes]

Hi Tom,

I can regulate 650 VDC with a high voltage version of the PR3 topology, which will work very well with a push-pull tube output stage.

This will be a custom design, as I will have to do a new board layout for this regulator to accommodate high voltage capacitors. However, it is a proven high voltage regulator design, as I have already used a 500 volt version of this regulator to regulate a 6L6 push-pull output stage and numerous tube preamps. The regulator will be very quiet with the same regulation capability of the PR3.

I will need to know the load current requirements to optimise the design thermally and to assess the cost. Also do you have any space limitations within the equipment chassis?

Use one regulator per channel, as this is a balanced output stage.

Regards
Paul

[serengetiplains]

Great, Paul.  I'll be regulating both the driver and output stages.  I'll thus need two regulators per stage, so four regs total:

• two for the driver 6SL7, one reg per two tubes; total load current for two tubes (4 triodes) is ~3mA; input V to the reg is 295VDC;

• two for the output EL34, one reg per two tubes; total load current for two tubes is ~60mA; input V to the reg will be 657VDC.

I have some space inside the chassis---enough for your PR3-sized regs.  I'll be adding another chassis in any event, so space isn't really a consideration.

[Paul Hynes]

Hi Tom,

The same module PR3HVDC can be used on both the EL34 and the 6SL7 supplies. The regulator dropout voltage is around 10 VDC so for the EL34 supply you will either have to find some additional DC input voltage or adjust the output voltage down a little to allow for this. Running at 640 volts should not upset the EL34 stage. I can do these high-voltage DC input modules for £100 each plus insured carriage and packing. I will mail you with shortly.

Regards
Paul

[serengetiplains]

Thank you, Paul.  The voltage dropout is not an issue; both the driver and output supplies can operate at 10VDC less at the tubes.

I have one question.  The 6SL7 driver is a basic series-triode set-up.  In a single 6SL7, the output of triode 1 is capacitively coupled from its plate to the grid of triode 2.  Triodes 1 & 2 share the same supply, very similar to this design but without the feedback loop:

http://diyaudioprojects.com/Tubes/12AX7_Preamp/

Would I see greater PSU noise reduction having separate regulators for the two halves of the 6SL7?  If so, and given the balanced design, I would then need two regs per channel for the driver tubes.  Reg 1 would supply triode 1 of two 6SL7s; reg 2 would supply triode 2 of two 6SL7s.  What do you think?

[Paul Hynes]

Tom,

You will get the best performance by having a completely separate regulated supply for each valve stage including the transformer winding. In other words each power supply is galvanically isolated. This will remove any ground return current inter-modulation caused by having a number of stages all powered from the same common supply. Use a local star ground for each valve stage with its own power supply referenced to this star ground. The signal ground follows the signal path. The ground return current stays out of the signal ground route to the next stage and therefore will not pollute its ground reference. This is a big upgrade over a common power supply for all stages, as it improves the musical presentation across the board, regarding image size, image stability, dynamic scale, and the intelligibility of the vital low-level information.

Regards
Paul

[serengetiplains]

Thanks for your advice, Paul.