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  1. Replies
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    It would be very unusual for the wiring to be...

    It would be very unusual for the wiring to be steel, but I guess it's possible. More likely it's tinned copper. As Helmholz notes, a magnet tells the tale.

    Solder plated steel has been used for...
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    The cheaper Asian restaurants often have...

    The cheaper Asian restaurants often have paper-wrapped pairs of chopsticks simply sitting in containers on tables or at the cutlery pickup. The two sticks are still joined at one end and you snap the...
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    It seemed patently obvious to me that a circuit...

    It seemed patently obvious to me that a circuit block that met the input/output specs of a reverb tank but was solid state inside was needed. So I went and looked. It's been a couple of years since I...
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    I also did a PCB to let a Beltone BTDR2 accept...

    I also did a PCB to let a Beltone BTDR2 accept almost all coil-tank input levels and output signal acceptable to most tank recovery circuits. That is - a BTDR tank replacement.
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    True, but then nothing succeeds like excess. :) ...

    True, but then nothing succeeds like excess. :)


    Sure.

    https://ethanwiner.com/filters.html

    Built one. Works. The only issue with using this in general for hum-killing is that different...
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    There is a hum suppressor that is a bit more...

    There is a hum suppressor that is a bit more work, but that would probably turn in good results. It involves generating 60, 120 180, and 240 hz from the power line, then feeding a variable amount and...
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    Humbucking is a way to use iron and copper to...

    Humbucking is a way to use iron and copper to pick up an equal non-signal hum and electronically subtract it from signal+hum. It's an exercise in cancellation. The classic humbucker pickup uses a...
  8. It's developed internal or external leakage. Note...

    It's developed internal or external leakage. Note that you also redid the solder joints on the ends of the cap leads, and if one of those was a cold joint, it could have become noisy as well.
  9. This is the issue I was referring to. If you use...

    This is the issue I was referring to. If you use a Y cable to connect the inputs of two amps in parallel, you guarantee that any issues with ground leakages in the two amps will cause hum problems if...
  10. Two boxes may make more sense than one. It...

    Two boxes may make more sense than one. It depends entirely on what the person can deal with in terms of running cables and not getting speaker cables and coaxial shielded cables mixed up. It is...
  11. Anything that can switch an AC line motor load...

    Anything that can switch an AC line motor load probably won't even get its hair mussed up with speaker loads from nominal tube amps. It ought to be fairly easy to protect this. You're right about...
  12. I missed the first part of this one. You need...

    I missed the first part of this one.

    You need to not leave the amps unloaded. Some, but not all, tube amps oscillate and destroy themselves with no speaker load. You can fix this issue by using a...
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    As Mr Fourier told us, any repeating signal can...

    As Mr Fourier told us, any repeating signal can be decomposed into a number, possibly infinite, of sines of various amplitudes. If you take a sine wave and do anything to its waveshape, the spectrum...
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    Absolutely correct. The quirky, nonlinear...

    Absolutely correct. The quirky, nonlinear dependence of the speaker's complex impedance and sensitivity and the crossover's components to get a clean changeover from the bass to treble is very...
  15. Looks like one of the output tube's cathode is...

    Looks like one of the output tube's cathode is connected to the speaker. That would do it I think.
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    OK, in the spirit of nuggets of information... ...

    OK, in the spirit of nuggets of information... :)

    A really common mistake made by many folks is that they don't account for the "invisible resistors". "Invisible resistors" are the internal...
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    Another source of mysterious hum that simply...

    Another source of mysterious hum that simply won't go away is mis-wiring of the center tap of the power transformer. This lead absolutely has to go to the negative terminal of the first power filter...
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    All I said was OK, fine, it doesn't matter....

    All I said was OK, fine, it doesn't matter. That's not a question.
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    I think I'd say that a different way. In this...

    I think I'd say that a different way.

    In this circuit, the pot is DC blocked at the wiper and has one end open. There can be no voltage >difference< across the pot, as it all floats at the same...
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    It's possible that you were on the edge of...

    It's possible that you were on the edge of motorboating. This is the low frequency equivalent of high frequency oscillation. You sometimes run into it if you keep increasing bass response in the...
  21. That is 100% true. It's CIRCUITS that affect the...

    That is 100% true. It's CIRCUITS that affect the sound.

    I'll insert my standard complaint about anecdotes: reputation is interesting, but by no means definitive. You can't measure reputation, and...
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    It's an interesting case in imponderables. I...

    It's an interesting case in imponderables. I think you're right J.M. - the real threshold would be when you get arcing to another electrode. 300V would be a good guess. Probably this varies a lot...
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    Sticky: Correct or not is hard to say. In an amp with no...

    Correct or not is hard to say. In an amp with no feedback from the speaker output, there is no particular reason to ground the speaker leads for the circuit's operation. You can ground one of them,...
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    The design of the E-I lamination and coils makes...

    The design of the E-I lamination and coils makes the magnetic field run along the length of the center leg of the E, then return through the outer legs of the E. Think of the field orientation as a...
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    Were you measuring your 400V at the first...

    Were you measuring your 400V at the first 22uF/450 or the second one?

    I guess, put another way, what are the current (sorry, meaning now) voltages on both caps.

    If the event opened the OT...
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    A transformer with 750ac across a ct high voltage...

    A transformer with 750ac across a ct high voltage output makes 375vac on each half secondary to be rectified. The UNLOADED voltage when rectified is 530Vdc peak, which agrees well with your 513...
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    There is one more step in the humdinger...

    There is one more step in the humdinger evolution. I'd have to go looking for where I saw this, but it was clever.

    There may be some level of hum you just can't get rid of by reasonable means....
  28. First, get that shorted speaker out of there....

    First, get that shorted speaker out of there. These amps don't have any clear protection against shorted outputs, and you could melt down the output transistors pretty easily. In fact, you have...
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