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  1. I think the 0V of the 12V supply should be...

    I think the 0V of the 12V supply should be grounded.

    Elevation is normally done by connecting the centre tap of the 6.3V winding to an elevated voltage. This could be the cathodes of the power...
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    Was the 1A fuse a fast blow type? I'm in the UK...

    Was the 1A fuse a fast blow type? I'm in the UK too. I have 4W, 15W and 30W amps running with 1A T mains fuses and they never blow. Do the fuses hold up now with the power tube inserted?
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    If you remove the jack plug from the guitar and...

    If you remove the jack plug from the guitar and touch the end contact with a finger does the amp make a loud hum? Try it with just the amp and cord first.
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    Reading the sentence before I assumed it was...

    Reading the sentence before I assumed it was peak-peak that was 1/3 HT.
  5. The Marshall circuit has a 750R screen supply...

    The Marshall circuit has a 750R screen supply resistor (the one between the two 50u caps). Your circuit looks like it has 470R. Changing it to 750R would lower the screen voltage a little but...
  6. The original 2061 ran the EL84s way over data...

    The original 2061 ran the EL84s way over data sheet spec. too. With nearly 400V B+ and a 125R cathode resistor it's almost guaranteed to red plate. That's how they were able to get 20W out of two...
  7. It will have horrible crossover distortion if the...

    It will have horrible crossover distortion if the cathode resistor is increased too much. It's better to reduce plate dissipation by reducing plate voltage not current (as Helmholtz said) I use a...
  8. Thread: Stabbed myself

    by Dave H
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    I've done that. I was working behind an old style...

    I've done that. I was working behind an old style TV in a tight corner and touched something live. My arm contracted back violently and smashed my right elbow on the wall behind. It still hurts...
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    You could try it like this. Connect the sig gen...

    You could try it like this. Connect the sig gen between the (guitar?) pickup and ground. Connect the cable under test to the pickup hot and ground. Terminate the other end of the cable with a 1M...
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    Thanks, I see it now. I must have been half...

    Thanks, I see it now. I must have been half asleep. It was way past midnight in the UK.
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    Thanks Enzo. Where does he say that? I missed it.

    Thanks Enzo. Where does he say that? I missed it.
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    Does this mean the -45V rail is OK? The +/-15V...

    Does this mean the -45V rail is OK? The +/-15V regulators are bottom left on the schematic. Pin 4 of the op-amps is -15V. Is it the -15V rail that reads 0.5V (or -0.5V)? You have to check the...
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    The -15V comes from the emitter of series pass...

    The -15V comes from the emitter of series pass transistor Q213 at the bottom left of the schematic. Also check Q211 as it's part of the -15V regulator circuit.
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    For a straight guitar to amp connection it should...

    For a straight guitar to amp connection it should be enough to just measure the cable capacitance as a measure of "quality" as all cables with the same capacitance will sound the same (ignoring...
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    That dot should be here - 58472

    That dot should be here -
    58472
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    I think it works by loading down the outputs....

    I think it works by loading down the outputs. Imagine the master vol pot (rheostat) is two equal resistors in series. The PI outputs are out of phase so the junction of the two resistors is always at...
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    I don't think it will be audible. The 500k...

    I don't think it will be audible. The 500k loading will just cause a slight attenuation of the signal.
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    Leave the kid alone!

    Leave the kid alone!
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    When working out the voltages and currents in...

    When working out the voltages and currents in guitar amp circuits you'll be using Kirchoff's all the time without realising.
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    All voltage sources have output resistance even...

    All voltage sources have output resistance even if it's not obvious. If you connect two voltage sources together the resulting voltage will depend on their respective voltages and output resistances....
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    It needs a resistor from the right hand side of...

    It needs a resistor from the right hand side of each coupling cap to ground.
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    I don't think it's a good idea to reduce the...

    I don't think it's a good idea to reduce the value of R88 to attenuate the signal as it has no other resistor to work with only the output impedance of the tube (35k?) You'd have to use a very low...
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    To reduce the gain of the blue channel I'd add a...

    To reduce the gain of the blue channel I'd add a resistor in parallel with the Blue Gain pot and increase the value of R112 so the frequency response is unchanged. If the parallel resistor is 47k (as...
  24. I must have been half asleep. I didn't see the...

    I must have been half asleep. I didn't see the posts below #9

    I just remember 1k drops 1V at 1mA so 1k at 50mA drops 50V
  25. Put the resistor in the B+ line where the 470 ohm...

    Put the resistor in the B+ line where the 470 ohm resistor is on the Princeton. The B+ current is 50mA so a 1k resistor will drop 50V. The resistor will have to dissipate 2.5W. I'd use a 5W or higher...
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    You only have to find components in the library...

    You only have to find components in the library the first time then they can be saved to either Custom Components, Custom Symbols or Favorites for quick access.
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    That's normal. Moving a screwdriver near the...

    That's normal. Moving a screwdriver near the pickup has the same effect as a vibrating string. It produces a voltage at the output of the pickup which disturbs the resistance reading.

    Edit:...
  28. You could just use a resistor and capacitor to...

    You could just use a resistor and capacitor to make a pi filter (like the 5D2 Princeton) to reduce both B+ voltage and ripple.
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