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  1. 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...
  2. 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...
  3. 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...
  4. 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...
  7. 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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    570

    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...
  13. 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....
  20. 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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    If you're going for the "artificial center tap",...

    If you're going for the "artificial center tap", yes, that works. Two 100R resistors in series, across the whole 6.3V winding, with the center connection between the two resistors tied to ground. The...
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    I'm still a little confused by the question, but...

    I'm still a little confused by the question, but maybe I can add some useful data.

    Is what you're thinking about an attempt to get lower hum? If so:
    > You have to have some kind of reference...
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    Yeah, give them a try. You're actuallyl buying...

    Yeah, give them a try. You're actuallyl buying Newark's assurance that these are quality devices. I trust Newark that much.

    @juan:
    Yeah, they were intended to replace TO-66s. I suspect that...
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    The "has spare capacity" on a 5V winding might be...

    The "has spare capacity" on a 5V winding might be a problem. If the 5V winding is powering a tube rectifier, nearly all tube rectifiers have the cathode connected to the heater. It floats on B+ in...
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    Wow! They're still around! Neat. I was...

    Wow! They're still around! Neat.

    I was expecting him to find a few on ebay for $50 each. I did a few amps early on with 40409/40410, and fixed a few others. The industry zoomed right past that...
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    Add to or mess with the values on the Zobel....

    Add to or mess with the values on the Zobel. Can't hurt, can it?
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    Possible? Sure. You'll run into several...

    Possible? Sure. You'll run into several difficulties, all of which are relatively well known. There are solutions for them, though.

    The 6.3V/3A winding can be full wave rectified into 6.3V*1.1414...
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    Oh. If the drivers are the 40409/40410 types and...

    Oh. If the drivers are the 40409/40410 types and are damaged, don't even try to get exact replacements. The combination TO-39 device and pressed on heat sink are unique. Count on using TO-220 devices...
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