Voltage doubler questions

[Aaron]

That cap hasn't shorted, but its only rated at 630v. I'm getting 273v AC before the cap then only 16v AC after it before the diode.

[martin manning]

I'd try replacing the cap.

[Aaron]

Thanks Martin, I replaced the cap and now I'm getting -80v.
But, thats only when i take out the 12BH7 driver. Put it back in and it drops down to -10. I've tried two different valves same result.

[martin manning]

That supply has too much source impedance to deliver any significant current. What does the driver schematic look like?

[Aaron]

Hi Martin,

I have attached the schem.
Valves are 12AU7-12BH7-KT88's.

Thanks,
Aaron

[martin manning]

So there are two bias supplies, and you are working on the one connected to the 12BH7 grids?

[Aaron]

The bias tap after the diode feeds the 47k resistors and bias pot feeds the 330k resistors. If that makes sense?

[martin manning]

Supplying all the current for the two 12BH7's is more than the capacitively coupled supply can provide. Is this a new design you are working on?

[Aaron]

There's only one 12BH7 for the driver tube.

I was going for a Dumbleland/SVT output, but with KT88's.

Here's a copy of the schematic it came out of,
[img1385]http://milas.spb.ru/~kmg/files/schemati ... 160_ps.gif[/img]

[martin manning]

Yes one 12BH7, but it has two triodes with ~10mA idle current. Notice in the 160PS the bias supply has a dedicated PT winding, and it is not capacitively coupled. Your situation is even more demanding, since you need a supply that is capable of providing grid current for the output tubes plus the driver tube current (like an SVT power section). I would consider adding a small transformer for the bias supply.

[Aaron]

Ahhhh, okay. Thanks Martin.

Back to the drawing board.

Aaron