Metropoulos Forum

Greetings folks,

I came across an old tube PA system (Knight brand) and I've been looking under the hood trying to figure it out. I had a question about the placement of one of the filter caps in the power supply, and was wondering if anyone had an answer.

The amp in question has a separate rectifier and B+ for the plates, the screens and the rest of the amp run off a different rectifier / transformer tap. I have a question about the placement of the plates filter cap. Instead of being connected to ground, this cap is connected between the plates B+ and the screens B+.

I made a schematic here, you can see the cap in question circled in red:

http://www.riscchip.com/guitars/power_supply.jpg" onclick="window.open(this.href);return false;

B+1 is 600 volts, B+2 is 400 volts. I'm guessing this was done simply because the plates filter cap is only rated 300v, and this arrangement places it in series with the screens cap for better voltage handling. Still...I'd rather beef up the filter caps and isolate the B+1 filter cap. Any reason that would be bad idea?

Thanks for any thoughts.

You can do that, but it won't sound as good.
The plate cap is in series with the screen cap, not just for voltage rating.

Cool...thanks for the feedback. Much appreciated.