Back-to-back transformers + bias tap voltage doubler. check?

[Michael Allen]

I put together a submini amp, using two 12V transformers back to back. So 110V - 12V - 12V - 110V. I made a bias tap by adding a diode bridge to the secondaries. The bridge is isolated from the secondaries with .1uF capacitors to prevent shorting as drawn up by Bruce in a previous thread.

So I'm not getting enough voltage out of the bias tap. I want to add a voltage doubler to it. I've drawn this schem up (poor quality from camera phone) and i have some questions.

I found the schem for the doubler (or is it quadrupler?) on the net. Do I still need to isolate this from the secondaries with the two vertical capacitors?

Will this work?

[R ski]

No you don't need to isolate the bias supply, the first transformer already limits the potential of power from the 115 vac wall plug.

[Steve Conner]

0.1uF capacitors are far too small, try 10uF or more.

You don't need any isolation unless you also want to use the winding for something else.

The two diode/two capacitor doubler should work fine, you'll get 12*2*the square root of 2 = about 30 volts DC, as opposed to 15V with a plain rectifier.

[guitardude57]

Here is a design that I want to try with an old PT that is giving me about 196 volts and 600mA.

This may work for you too.

Anyone know which diode and cap values I would need to get this PT closer to 400V?