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G3PIJpeter · 6th Nov 2019, 3:36 pm

The PSU works OK so none of the passive components can be that far out. My main question is about the specification: 200-210 VDC out - but at what maximum current?

The EL34 is used as a series-pass element and its maximum anode current is given as 91 mA. From this, is it OK to assume that the PSU is rated at a nominal 100 mA? The EL34 maximum anode dissipation is 25 W: it can drop 250 V at 100 mA before exceeding this dissipation, which allows the unregulated voltage to be 220 + 250 = 450 V. I have measured 540 V unregulated but that was at zero load. . . . . . perhaps I am answering my own question here!

It would still be nice to have sight of a circuit diagram to save tracing it out. Then I can replace the EL34 with an S11E12 and sell the EL34 to the audio brigade. Also - why does it have 2 x 12AX7 instead of the much simpler EF91 or similar? None of the standard circuits that I have seen uses a pair of double triodes.

Peter G3PIJ

6th Nov 2019, 3:36 pm	#3
G3PIJpeter Hexode Join Date: Nov 2011 Location: Chippenham, Wiltshire, UK. Posts: 323	Re: Roband Electronics M34 PSU The PSU works OK so none of the passive components can be that far out. My main question is about the specification: 200-210 VDC out - but at what maximum current? The EL34 is used as a series-pass element and its maximum anode current is given as 91 mA. From this, is it OK to assume that the PSU is rated at a nominal 100 mA? The EL34 maximum anode dissipation is 25 W: it can drop 250 V at 100 mA before exceeding this dissipation, which allows the unregulated voltage to be 220 + 250 = 450 V. I have measured 540 V unregulated but that was at zero load. . . . . . perhaps I am answering my own question here! It would still be nice to have sight of a circuit diagram to save tracing it out. Then I can replace the EL34 with an S11E12 and sell the EL34 to the audio brigade. Also - why does it have 2 x 12AX7 instead of the much simpler EF91 or similar? None of the standard circuits that I have seen uses a pair of double triodes. Peter G3PIJ