What is the plate current through the 2A3 in stock Stereomour II?

[Paul Birkeland]

The 30A likes high plate voltage and a lot of current.  The plate of a tube loaded with a C4S can't swing above the incoming voltage to the C4S, but with a plate choke this is possible.

[Deke609]

Thanks PB. I think I get that.  So that rules out C4S loading. But isn't shunt reg still possible, provided the regulator can handle the voltage and current?  Or does the voltage swing of the plate choke conflict with voltage regulation? Linear Audio makes a high voltage shunt reg pcb that can output 600+ VDC at 200+ mA. I was thinking of using it to regulate the plate voltage on the EML 45B by placing the reg between the power supply (post rectification and some smoothing) and the plate choke. Would this not work?  If it's workable (and useful) I could use a separate reg for the EML 30A.

cheers and many thanks, Derek

[Paul Birkeland]

A shunt regulator needs to operate at a lower voltage than B+, and you will need to pass the operating current of the 30A (which is usually pretty high), plus some current for the shunt regulator to operate.  The extra current will heat up the C4S part of the regulator.  You could raise the regulated voltage to help reduce the heat across the C4S.

[Deke609]

Hmm. But stepping back, I'm not sure I want to go without a CCS loaded driver. My mostly uneducated understanding is that (1) a CCS presents such a high impedance to AC that it effectively produces a ruler flat load across all audible frequencies, and (2) no plate choke can compete with that.

So that suggests going with the 5670.

Question: can one run two distinct B+ lines off the same power transformer HV secondary? More specifically, one line via a voltage doubler and a second via a tripler?  I have in mind using the tripler to feed a CSS loaded EML 30A - but that presumes I can find a CCS design that can handle a lot of voltage. I've searched before (hoping to CCS load an output stage) and never found one, or even mention of one. So maybe this is pie-in-the-sky.

cheers and thanks, Derek

[Paul Birkeland]

The issue you may run into with a voltage tripler is that the AC current from the power transformer necessary to run the 20mA of driver current will be really high.