Input voltage on 5E3 clones

Discussion in 'Amp Central Station' started by mherrcat, Feb 27, 2018.

  1. mherrcat

    mherrcat Tele-Holic

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    I have been reading about the “benefits” of lowering input voltage for vintage amps like the 5E3. I can see using one on a vintage amp that was designed around 110V input.

    My question is about modern transformers in current 5E3 clones. I have a 5E3 clone with a Mercury Magnetics FTDP-MM power transformer with a spec of 335-0-335 unloaded with an input voltage of 120V. Is there any benefit to using a voltage regulator/variac to lower the input voltage on an amp like this? Or would lowering the heater voltage in the process be undesirable?

    My wall voltage is about 120V to 121.3V depending on the outlet I am measuring.
     
  2. dan40

    dan40 Tele-Afflicted Silver Supporter

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    If it is a new, voltage compensated PT then I would not bother lowering voltages unless the filament voltage was unusually high.
     
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  3. CoffeeTones

    CoffeeTones NEW MEMBER!

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    Do you recall what the plate voltage is with that Mercury power transformer at your normal wall voltage? Thanks
     
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  4. printer2

    printer2 Poster Extraordinaire

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    And your heater voltage.
     
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  5. mherrcat

    mherrcat Tele-Holic

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    I'll have to check. It's been a while since I had the chassis out of that cabinet.
     
  6. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    Whatever you do DON'T do it with a Variac for more than test purposes. Use a Voltage Regulator. A Variac is simply a large rheostat - a huge pot - and is not stable. They can fluctuate and be easily bumped to the wrong setting. They should never be used for extended periods.
     
  7. printer2

    printer2 Poster Extraordinaire

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    I have a rehostat where the previous person drilled a hole (I am sure they mitigated for the shavings) just past 120V, I am guessing to insert a screw so the knob could not be rotated further. Quite possibly he he had an issue at some time.
     
  8. mherrcat

    mherrcat Tele-Holic

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    Outlet = 121 VAC
    Rectifier = 5Y3GT
    B+1 = 337 VDC
    B+2 = 298 VDC
    B+3 = 219 VDC
    Plates = 327/324 VDC
    Heater = 6.3 VAC
     
  9. SacDAve

    SacDAve Poster Extraordinaire

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    Those voltages look low
    5E3_Voltages.png
     
  10. mherrcat

    mherrcat Tele-Holic

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    With 5V4GA rectifier:

    Outlet = 121 VAC
    B+1 = 364 VDC
    B+2 = 323 VDC
    B+3 = 236 VDC
    Plates = 353/350 VDC
    Heater = 6.3 VAC

    I’m not an electrical engineer, so any thoughts on the efficacy of either scenario are welcomed.

    Again, the PT is Mercury Magnetics FTDP-MM 335-0-335. OT is Mercury Toneclone FTDO-59.
     
  11. mherrcat

    mherrcat Tele-Holic

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    Bumping this up 'cause I'm interested in hearing thoughts on using the 5V4 rectifier as opposed to the 5Y3...

    Here are the numbers again:

    Outlet = 121 VAC
    PT = 335-0-335

    Rectifier = 5Y3GT
    B+1 = 337 VDC
    B+2 = 298 VDC
    B+3 = 219 VDC
    Plates = 327/324 VDC
    Heater = 6.3 VAC

    Rectifier = 5V4GA
    B+1 = 364 VDC
    B+2 = 323 VDC
    B+3 = 236 VDC
    Plates = 353/350 VDC
    Heater = 6.3 VAC
     
  12. DrPepper

    DrPepper Tele-Afflicted

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    Yeah, shoot for 6.3 - 6.9 on the filaments...
     
  13. DrPepper

    DrPepper Tele-Afflicted

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    As long as the transformer can handle the current requirements of the 5V4 go with what sounds best to you...
     
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