help deciphering weird power supply

Discussion in 'The Workbench' started by Rockbert, Sep 17, 2020 at 1:50 AM.

  1. Rockbert

    Rockbert Active Member

    Joined:
    Feb 4, 2009
    Messages:
    358
    Likes Received:
    97
    Location:
    California
    I'm rebuilding an old PP 6L6 PA in to something with a vaguely Marshall front end, and I ran into a weird power supply. Can't quite figure out what's going on. It has a PT with a 145V secondary and a voltage doubler. It's almost like a typical half-wave voltage doubler, but not quite. I've retraced it like 5 times because I'm sure I got it wrong, but no it's right. Schematic attached. Seems to be missing a series diode, and I can't figure out what that other diode to ground is doing. Or why there's that 5.6ohm resistor in there.

    I may just leave it alone since it seems to work, but I'd like to understand it better if anyone can help explain what's going on, thanks!

    ps.png
     
  2. thetragichero

    thetragichero Well-Known Member

    Joined:
    Jun 6, 2010
    Messages:
    2,625
    Likes Received:
    732
    Location:
    flo rida
    it's a voltage doubler. I've got 4 bogen PAs that use the same thing. copy what you see for the first node and then adjust dropping resistors and filter cap values to suit your needs
     
  3. Rockbert

    Rockbert Active Member

    Joined:
    Feb 4, 2009
    Messages:
    358
    Likes Received:
    97
    Location:
    California
    Thanks, that's pretty much what I'm planning to do, just trying to get my brain around how the circuit works on each half of the cycle. This seems to differ from the "textbook" doublers and the Bogen's I've looked at, it has the diodes and the capacitors in the opposite location. Like if you switch the position of the diodes and caps in this schematic, you have the CHB35A power supply. Maybe that's what's throwing me off.
     
  4. thetragichero

    thetragichero Well-Known Member

    Joined:
    Jun 6, 2010
    Messages:
    2,625
    Likes Received:
    732
    Location:
    flo rida
    yeah they should be functionally similar. i wouldn't bother with a 400v and 200v capacitor there. probably easier and cheaper using two 450v there (I'd rather overspec than underspec and usually only stock 450v+ filter caps anyway)
     

Share This Page