Getting bias vltage from a non-centertapped secondary

[booj]

AC voltage from the secondary is 391 volts. The original bias winding supplys 33 volts which gives about -44 volts bias which is just shy of what I need. (Thje cust. supplied me with #7 GT Mullards) The plate supply is about 515 volts.
I figure a couple of 220k resistors from ground to each leg of the secondary would provide an artificial ground to supply source voltage.
'twould be nice to get another opinion.

[Albert Kreuzer]

I suggest you use the original bias winding and a voltage doubler.
If you are dead set on using the HT, look how Marshall and Ampeg did it.

Someone (Rick Erickson?) posted this some time ago, maybe it helps:

[booj]

Yea, the voltage doubler would work fine. Marshall and Ampeg use center tapped secondarys. This amp has no center tap.
Thus the question, which is how to get voltage from an ungrounded transformer winding. I'm thinking capacitive coupling?

[Steve Conner]

We just covered the ungrounded winding thing in this thread:
http://music-electronics-forum.com/t17788/

Also see schematics of Bogen PA amps.

But what you REALLY want is the voltage doubler on the existing bias winding. You add one more diode and one more capacitor et voila, the bias voltage is doubled. Works great to convert an EL34 amp to 6L6s. See Fig. 4.44 here: http://www.tpub.com/neets/book7/27m.htm

Note the schematic there gives a positive output. You need to turn the diodes around for a negative output.

[booj]

I did the voltage doubler on the bias circuit.



I drew in what I did just above the original bias circuit.

I'm not sure if the thread mentioned by Steve was actually answering my question, since it seems the guy wound up with a voltage doubled main HV sorce.
Thanks guys.