Question on the Champ 5C1 power supply

Discussion in 'Shock Brother's DIY Amps' started by vvelt, Feb 22, 2020.

  1. vvelt

    vvelt TDPRI Member

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    Hello, I have this breadboarded with the power supply like in the schematic. The last filter node supplies both the screen of the 6V6 and the plate load for the 6SJ7. It sounds fine this way and it's dead quite, but my screen voltage on the 6V6 is only 270v while the plate is at 324v. I'm using a smaller power transformer for this hence the lower voltages. I've also tried adding another filter node with a 1k resistor and 10uf cap to feed the screen and my screen voltage goes up to 317v. Is it better at the higher voltage or is running the screen on the low side for the 6V6 OK?

    I've also tried feeding the screen of the 6V6 from the 2nd filter node that goes to the OT, but I got a lot of hum that way. Any thoughts on which way is better?



    champ_5c1.png
     
  2. elpico

    elpico Tele-Holic

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    That's okay, and it's the way they designed it (the layout drawing says fender got 280v on the screen with the particular tubes they tested with). It's your amp though and if you prefer the sound of it with the screen voltage higher that's fine too. A third option is to use the higher screen supply voltage but add a screen resistor, which will provide more protection to the tube. You'll find this option was the one taken in Fender's champ reissue, they used a 305V supply with a 470ohm 2w screen resistor.
     
    Mr Ridesglide, Paul-T and vvelt like this.
  3. vvelt

    vvelt TDPRI Member

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    Thanks!
     
  4. vvelt

    vvelt TDPRI Member

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    Ok, so I tried the power supply a few different ways just to see:

    1st node to OPT, 2nd node to screen, 3rd node to preamp = hums badly
    1st node prefilter only, 2nd node to OPT and screen, 3rd node to preamp = hums badly
    1st node prefilter only, 2nd node to OPT, additional node* to screen, last node to preamp = screen voltage is up
    1st node prefilter only, 2nd node to OPT, 3rd node to screen and preamp = screen voltage low but sounds good

    The last way is how it's shown in the Fender schematic and I think I'm going to leave it this way. Adding another node for the screen does bring up the screen voltage but I'm not sure if this is an improvement or just uses up more parts.
     
  5. elpico

    elpico Tele-Holic

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    If it aint broke right? Have fun with it.
     
  6. sds1

    sds1 Tele-Afflicted

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    What about decreasing the 25K drop to say between 1K and 4.7K? Then your screen (and preamp) voltages both go up with same filtering. Could be fun to try.
     
  7. vvelt

    vvelt TDPRI Member

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    That's a good idea, I'll try that just to see.
     
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