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5e3: 310vac Pt

Discussion in 'Amp Tech Center' started by itsa68, Mar 16, 2016.

  1. itsa68

    itsa68 Tele-Meister

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    "Sounds right"
    [​IMG]
     
  2. itsa68

    itsa68 Tele-Meister

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    Good news everyone! I have fresh voltage measurements!

    Ac in: 308vac
    After rectification: 322vdc
    So b+: 322v
    B+2: 290v
    B+3: 226v

    6v6 (1) is as follows
    Pin 3 (b+ through OT): 317v
    Pin 4: 289v
    Pin 6 (bias): 18v

    6v6 (2) follows
    Pin 3: 310v
    Pin 4: 286v
    Pin 6: 18v

    12ax7 stage one
    Cathode: 160v
    Bias: 1.1v

    Stage two
    Cathode: 137v
    Bias: 1.3v

    Stage 3 (phase inverter)
    Cathode: 182v
    Bias (anode): 46v

    Any comments or suggestions welcome! Thanks folks
     
  3. itsa68

    itsa68 Tele-Meister

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    I still have not seen a 5e3 use a power transformer with such low secondary voltage. My hunch is that I need a 350Vac PT instead of this one, which looks like a 300v. However, I'm a bit strapped for cash right now so I won't be able to order another one in order to test this theory.
     
  4. mozzman

    mozzman Tele-Meister

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    You originally said you were getting 414 for b+, without tubes.

    A 5v4 will bring it up, but you may need solid state diodes to get it much higher. You can wire 2 diodes in a old tube socket and plug it in.

    It will also work fine with 322v , just maybe a bit dirty.
     
  5. robrob

    robrob Poster Extraordinaire Ad Free Member

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    A GZ34 rectifier will boost the voltage almost as high as solid state so if you want to stick with a tube give that a try.

    How does the amp sound? Still have the ratty tone?

    How is the circuit grounded to the chassis? You need a big iron to solder directly to the chassis or you can end up with a cold, noisy joint.
     
    Last edited: Apr 5, 2016
  6. robrob

    robrob Poster Extraordinaire Ad Free Member

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    I hate to say it but your layout is nowhere near optimal. I would have put the rectifier in the upper left "empty" socket and drilled some new holes to put the tone and volume pots over by the preamp tubes. As someone stated earlier, your layout may be conducive to oscillations, noise and hum.

    [​IMG]
     
  7. itsa68

    itsa68 Tele-Meister

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    After assembly, I've been realizing the gravity of my layout sins. I did update the heater and grounding schemes with notable improvement. But if the general layout of the amp needs to be changed, perhaps I'll disassemble and reassemble soon. Ah well, this is how we learn!

    I plugged the 5u4 back in earlier today with no sound improvement. I could check the voltages later.
     
  8. dankilling

    dankilling Tele-Afflicted Silver Supporter

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    Your voltages actually look ok- definitely within 20%. Is it still 'flarping?' And by Pin 6 (bias) you mean Pin 8, right?
     
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