5U4 --> 5Y3 in a Recto?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Beam Tetrode, Oct 13, 2006.

  1. Beam Tetrode

    Beam Tetrode Member

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    Hi,

    I have a 3 channel Mesa Dual Recto which runs 4x6L6 and 2x5U4 as stock.

    I prefer to run the amp with 2x6L6 (observing push-pull operation) and 1x5U4. I use the 4 ohm tap with an 8 ohm speaker. I always use the 'spongy' AC power setting. All together, it sounds pretty cool.

    Would it be safe to run 2x6L6 and 1x5Y3?
    Why exactly does a 5Y3 'sag' more than a 5U4?

    Thanks!
     
  2. jetlag

    jetlag Member

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    The 5Y3 doesn't have the current handling capability for larger amps like yours. It'll work for a little while, then smoke. If you want more sag, try a 5R4G recto or a GZ37 (the former is much cheaper).
     
  3. Beam Tetrode

    Beam Tetrode Member

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    What about 2x5Y3 and 2x6L6?
     
  4. Blue Strat

    Blue Strat Member

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    That would probably work. In the '50s, there were numerous cheap PA amps that used 2 6l6s with one 5Y3. With your amp, I'd feel safer with 2 5Y3s or maybe one 5V4.
     
  5. Beam Tetrode

    Beam Tetrode Member

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    In certain amps with two rectifier sockets, would it be safe to mix types? For example, could I run 1x5U4 and 1x5Y3 together with 2x6L6 in my Mesa? Just curious at this point...
     
  6. Leftee

    Leftee Guest

    Or 2 6L6's 2 5Y3's. :D

    http://www.leftee.net/images/boggy_IV_chassis_front.jpg
     
  7. Beam Tetrode

    Beam Tetrode Member

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    Thanks, that makes sense. I have a related question:

    I've been using a Fender 5D8 Twin with 2x5Y3 and 2x6L6 cathode-biased. I guess the amp was meant for 110VAC operation, 'cause the amp runs hot. Every voltage is high, and so is the bias.

    Could I use a different rectifier tube in place of the 2x5Y3 to lower the voltages? Maybe it would be better to use a variac...
     
  8. Leftee

    Leftee Guest

    I'd run a variac with that one.
     
  9. Blue Strat

    Blue Strat Member

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    There's no rectifier that I know of with the same pinout that would lower the voltage more than a 5Y3.

    I wouldn't worry about the voltages since they're probably already lower than spec with the 5Y3s. If the bias is to hot, increase the cathode resistor value about 30-50%. This is about a $1 mod.
     
  10. Beam Tetrode

    Beam Tetrode Member

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    All of the internal voltages are higher than spec with the stock 5Y3s. Even the heater supply is higher than normal. What is your recommendation for a Variac? Built-in output voltage display would be a useful feature...
     

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