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Would a SE single 6V6GT Princeton Reverb be the equivalent of a...

Discussion in 'Shock Brother's DIY Amps' started by DrPepper, Apr 13, 2021.

  1. DrPepper

    DrPepper Friend of Leo's

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    Milkman Halfpint? I love the sound clips. So, if I were to build a PR and use a SE OT and one power tube, would that get met close?

    If so, I would be dropping the PI section.

    But, should it be cathode biased or, fixed biased?

    I have a PR chassis and cab, hmmm...
     
  2. Uncle Daddy

    Uncle Daddy Tele-Afflicted

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    Do you want those 6 watts to be like a Tweed Champ, or more like a Vibrochamp?
     
  3. radiocaster

    radiocaster Poster Extraordinaire

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    You'd have to drop the tremolo because it wouldn't work as a single-ended amp. The Vibro-Champ uses a different circuit for it.
     
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  4. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I don't find a schematic for the Halfpint.
    Since it is single ended I imagine it is a vibrochamp-ish variant???
     
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  5. DrPepper

    DrPepper Friend of Leo's

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    Thanks... Yes, I guess it would be like a VC with reverb... time to start looking at schematics...


    So, a VibroChamp with reverb built in a PR chassis and in a PR cabinet with a 10" Celestion Gold it will be... more to come...
     
  6. NTC

    NTC Tele-Holic

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    A Champion Reverb.
     
  7. printer2

    printer2 Poster Extraordinaire

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    [​IMG]

    Just for curiosity sake.
     
  8. DrPepper

    DrPepper Friend of Leo's

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    Love it... Got a schematic?
     
  9. DrPepper

    DrPepper Friend of Leo's

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    Got the Milkman just about figured out thanks to printer2... Fixed bias, I don't need the power scaling.
     
  10. printer2

    printer2 Poster Extraordinaire

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    What do I look like, the Fairy Godmother?

    Ah, see your later post, seems you have been busy. Let's see how we both fared.

    The first tube and parts going to it is, Input Stage - BF tone stack - Gain Stage. The left side of the board is hooked up to the Speed and Intensity pots, I would guess that the circuit there resembles the Fender values. Three ceramic caps, obviously the oscillator. To the right of it the cathode bias resistor and bypass cap. Now what happens with the reverb? It could be a one tube design, one half the 12AT7 as driver and the other half recovery. Right of the trem circuitry is a bypassed cathode resistor, right of that is a coupling cap. These are going... ...to the other triode of the Trem circuit. So they are only using a single stage and not the cathode follower as in the Vibro Champ. They are using this triode as reverb recovery. Maybe.

    The coupling cap of this stage has a blueish wire running along the top of the board, seems to be going under it and to the 6V6. So where does the grid of this stage go? Following the yellow wire it goes under the board and is almost not visible coming up through a hole beside the coupling cap with the three resistors and the mica capacitor. I would hazard a guess that the cap is the 10 pF with a 3.3M resistor going to, the coupling cap of the second gain stage. We need a grid bias resistor to ground, the lower resistor goes to what looks like a ground, the upper resistor goes to the Reverb pot. The other mixing resistor that goes with the 3.3M.

    So that leaves us with the 12AT7. The power goes into the grommet, comes to a plate and the cathode of it goes to a resistor biased with a cap. It's grid is coming from a resistor that goes to ground and a mica cap to the coupling cap of the second stage. Typical Fender reverb although it looks to be only one side of the tube. The other triode is a gain stage with its coupling cal going to the Reverb pot also. The cathode resistor and bypass cap is going to ground by what looks to be a effects loop. No, none of that makes sense. Step back and look at the big picture. The grid of this triode seems to go, to the grommet. So this triode is the recovery, the line to the reverb pot makes sense. So a one tube reverb. So what is left? Right, the tremolo, where is it hooked up? A resistor comes off of the intensity (depth) pot, can't see where it goes. Looks like the last gain stage output does not go directly to the 6V6 but to a turret with the resistor from the depth pot on it. So varying the bias of the 6V6?
     
  11. DrPepper

    DrPepper Friend of Leo's

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    From first seeing the pic I was not aware that it was a Milkman, once I zoomed in I could tell...

    What can you make from the bias circuit for the 6V6, looks like bias vary trem and not cathode biased power tube (look at pin 8)... where's my fairy Godmother?
     
  12. printer2

    printer2 Poster Extraordinaire

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    The brown wire of of pin 8 goes to the electrolytic and the the ceramic resistor. So no question there. Looks like they are elevating the heaters off of the cathode resistor. The signal wire from under the board goes to pin 1 and then across to pin 5 using a grid resistor. So what is missing from this picture? The grid to ground resistor. It has to be the one going to the Depth pot. And since we are there, why not add some trem? Now not a single ended amp, the Traynor Guitar Mate YGM1, is cathode biased and it has the trem sent to the output tubes grids.

    https://www.thetubestore.com/lib/th...ynor/Traynor-Guitarmaterev-YGM1-Schematic.pdf

    I think Gibson did that also but I am too lazy to look it up.

    Or maybe it was Ampeg?

    http://www.stagecue.com/ampeg/schematic.jpg

    This one is cool.

    https://www.thetubestore.com/lib/thetubestore/schematics/Ampeg/Ampeg-J12T-Amp-Schematic.pdf
     
    Last edited: Apr 14, 2021
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