1969 With Low Plate Voltage

Discussion in 'Building the Classics' started by Chris4189, Nov 5, 2019.

  1. Chris4189

    Chris4189 Well-Known Member

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    How the hell do I wire the pilot light? The replacement I got from Valvestorm is a 120 volt. They have the red 120 tap going to the board where the death cap was and have the orange common going to the Bottom of the polarity switch.

    Which of these wires can I zip tie in order to clean this mess up a bit?
     

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  2. Chris4189

    Chris4189 Well-Known Member

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    So, I would tweak the 47k then correct?
     
  3. ampmadscientist

    ampmadscientist Well-Known Member

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    Yes.
    Start w/ 47K and see where pin 5 is at.
    -52 volts is about where 6550 should be on pin 5.
    -44.5 is about where EL34 should be on pin 5.

    But ya know, there is variations in power tubes and this is normal.
    That's why tubes are matched into sets.
     
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  4. Chris4189

    Chris4189 Well-Known Member

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    Brother I cannot thank you enough! I learned a good deal and hopefully tomorrow will be able to play this bad boy!
     
  5. ampmadscientist

    ampmadscientist Well-Known Member

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    the pilot light can be wired directly to the power switch if you have usa 120v power.
     
  6. Chris4189

    Chris4189 Well-Known Member

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    Yes, on the 120. I live in Virginia.

    According to George’s instructions you solder the red wire onto the power switch which I did and then put the black wire onto the mains fuse which I did. Plug the amp in light comes on. Turn the amp from off to on light goes off.
     
  7. ampmadscientist

    ampmadscientist Well-Known Member

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    1959 powersupplypilotlt.png
     
  8. ampmadscientist

    ampmadscientist Well-Known Member

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    Yes, on the 120. I live in Virginia.

    Near Herndon?
     
  9. ampmadscientist

    ampmadscientist Well-Known Member

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    Does the pilot light work now?
     
  10. Chris4189

    Chris4189 Well-Known Member

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    Somewhat. I live in the Shenandoah Valley right off I-81. I’m probably about an hour south of Herndon depending on traffic.
     
  11. Chris4189

    Chris4189 Well-Known Member

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    27B6C62A-2056-4070-9A16-A0C6B45DFF1B.jpeg
    I haven’t tried it yet but if I’m reading the schematic right the red wire would go to the 120 tap on the death cap board and the black wire goes to the main fuse?
     
  12. ampmadscientist

    ampmadscientist Well-Known Member

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    Shenandoah? That's fucking awesome.
    We used to drive there all the time and cruise around when I was in High school.
    It's a disconnect from city existence that's for sure..
     
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  13. Chris4189

    Chris4189 Well-Known Member

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    Are you still in NOVA?
     
  14. ampmadscientist

    ampmadscientist Well-Known Member

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    no im in central coast ca
     
  15. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    @Chris4189
    It seems or looks like the issue with the indicator/pilot light is that your amplifier has both the fuse and POWER switch in the neutral AC supply line.
    The indicator/pilot light will work correctly if you move its black wire to the other side of the POLARITY switch with the other black wire that is already there.
    It looks like the indicator/pilot light red wire is connected to the other side of the POLARITY switch via link to POWER switch.
     
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  16. Chris4189

    Chris4189 Well-Known Member

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    That did it!!

    I seriously can’t thank all those the helped enough! This is the first amp I’ve “tore into” and it’s been a learning experience. My goal one day is build an amp from ground up like many of you do.
     
  17. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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  18. Chris4189

    Chris4189 Well-Known Member

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    OMG! Now I’ve hardly got any volume! Biased, plug into my Fryette powerstation and with the amp dimmed I could barely hear it. Unplugged from the attenuator and with volume on 10 it’s like I was playing a 1 watt amp turned down for sleeping babies.

    Bet I got a bad power tube.
     
  19. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Try this.
    Crank your amplifier to 10 as before and measure pins #5 of the power tubes for VAC.
    What measurements do you read?
     
  20. Chris4189

    Chris4189 Well-Known Member

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    -48.7 VDC with power tubes out and cranked to 10

    I’ve tried several different quads of known good power tubes and same thing. Very low volume and obviously no break up.
     

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