Using an imbalanced PT.

[Alan0354]

Good to know.
Nice statement but you don't give any reason for it

Don't worry, in *this* case it will work.

I did post that I measure about 13V across both 250V resistors in the schematic in post #7. This proved the two Red wires source almost identical current. So each side is providing 50% of the power. That's the reason I don't need to derate the transformer with the circuit I posted in post #7. The important thing is the two resistor that drop voltages. This will correct the difference of voltage between both sides.

The "magical solution" would be to short together R/Y and B/R wires to recreate the original (missing) center tap .... except that you would be shorting the bias winding and magnetically all transformer windings are in parallel so it's a no no.

That's what I was guessing in the former post. Instead of shorting the Red/Yellow and Blue/Red wires, I would put two inductors in series across this two wires. The inductor has to be like 4 henrys. So at 60Hz, the reactance is 2 X 6.2832 X 60 X 4=3Kohm. So at 60Hz, it only draw 45V/3000=15mA. But at DC, it's like shorting the Red/Yellow and Blue/Red wire to get the CT. The inductor don't have to be too big as long as it can handle 150mA.

I thought of this already, but as I said, unless I change to cathode bias, I need the 45VAC tap. I already designed in the power scaling with scaling grid voltage, that would be a bigger change than I like.

[J M Fahey]

If you use the transformer as a full wave rectified 2 diode supply (you are already doing that) ), you don´t actually *need* a bias tap, you can use a resistive voltage divider from the HV tap, what Marshall does.

And you can "Power Scale" that bias voltage if needed.
So no big problem.

[Alan0354]

If you use the transformer as a full wave rectified 2 diode supply (you are already doing that) ), you don´t actually *need* a bias tap, you can use a resistive voltage divider from the HV tap, what Marshall does.

And you can "Power Scale" that bias voltage if needed.
So no big problem.

Ha ha, I use the -45VAC to get -63VDC to power the high voltage opamp in my design. I was really debating using cathode bias, I went fixed bias on this. It's just too much hazel to change this at this point.