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    It needed a new cabinet. It was under warranty.

    It needed a new cabinet. It was under warranty.
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    I had an issue like this on a (almost new) Fender...

    I had an issue like this on a (almost new) Fender Hot Rod that Fender could not figure out where the problem was. It turned out to be a crack in the cabinet under the amp chassis where it was hard...
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    The 80V supply is not regulated. This is hardly...

    The 80V supply is not regulated. This is hardly unusual for a non hi-fi audio amplifier. Also, given the very low source, winding resistances and leakage inductance I wouldn't be surprised if it out...
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    The is about the cheapest lowish distortion idea...

    The is about the cheapest lowish distortion idea I can come up with:
    55380

    Taken from pg 12 of this TI app note

    55381

    An output level control would be an essential addition.
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    You will need two ( or a dual output supply). As...

    You will need two ( or a dual output supply). As Juan said, it may be possible to get an estimate looking at the schematic, thanks for that. It can get a bit time consuming and is prone to error.
    ...
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    Hook it up to a bench power supply and measure...

    Hook it up to a bench power supply and measure the current demand for the +15 and - 15V rails. Next look as the physical size of the transformer. Go and search for transformers of that size with...
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    New amp -> new problems -> start a new thread to...

    New amp -> new problems -> start a new thread to avoid confusion.

    You made the measurements so lead the new thread with your results.
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    If you have an ohmmeter, check the DC resistance...

    If you have an ohmmeter, check the DC resistance of the pickup while tapping it. I suspect it has a coil with a break and vibration is causing it to make and break contact.
  9. X-Rays are electromagnetic waves and so are not...

    X-Rays are electromagnetic waves and so are not affected by magnetic fields to the best of my knowledge.
  10. I guess I was really trying to get a number for...

    I guess I was really trying to get a number for the time averaged power and on reflection that's not really what the OP looking for.

    That's interesting about the 10% increase on limit for music....
  11. These amps are not used to produce continuous...

    These amps are not used to produce continuous full power so for that reason an input power of 170W (350mA at 480V) is conservative, not that there is anything wrong with that.

    I find a pretty...
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    Call them and ask. There's no shame in outright...

    Call them and ask. There's no shame in outright replacement and it's sometimes a less expensive route. Might be a good time to update your profile with your location so others can chip in if they...
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    Well it's good progress - you crossed a big...

    Well it's good progress - you crossed a big hurdle. I think a new thread is probably a good idea.

    This a Berhinger Europower mixer, right?
  14. The has happened to me on more than one occasion,...

    The has happened to me on more than one occasion, although not from Marshall.

    I have noticed that most packages nowadays arrive in an oversized large single walled box with perhaps a couple of...
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    It sounds like you've been pretty thorough and...

    It sounds like you've been pretty thorough and that bodes well.

    A bulb limiter is easy to make. Just search for it.

    On the gate voltages, first measure the supply voltage between pins 1 and 4...
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    I think either will work. Did you check all...

    I think either will work.

    Did you check all the other components listed? I should add C15 to the list but that would be a rare failure.

    For the first test, remove R11 (or R12) to disable the...
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    Check T3 and T4 for shorts. If either is bad...

    Check T3 and T4 for shorts. If either is bad check all associated driver components i.e T1, T2, T5, T6, R1, R2, R28, R5, D24, R29, R7, D25 and IC1. When one of these FETs blow it often takes a bunch...
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    I've done this in the past by using an...

    I've done this in the past by using an inexpensive dual 50uf + 50uf 500V radial can cap plus a single axial 47uF 500V.
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    The problem is it takes a long time to research...

    The problem is it takes a long time to research and compare parts. Per my comment above I suggest you find one with a lower forward voltage drop. I don't think the switching speed is crucial,...
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    The cap is in the feedback path. If it develops a...

    The cap is in the feedback path. If it develops a higher than designed-for internal resistance then you will have too much feedback at higher frequencies. If you also have an extra 180 degrees of...
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    Do you see oscillation on the speaker out? ...

    Do you see oscillation on the speaker out?
    What if you turn the master to zero?
    Does it still happen if you have so speaker connected?
    What are the characteristics of the probe you are using?
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    It's close but the forward voltage drop is quite...

    It's close but the forward voltage drop is quite a bit higher. Therefore the power dissipation will be significantly higher too. That might not matter if the thermal margins are good.
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    But one input is 5Meg and the other is 5K! Why...

    But one input is 5Meg and the other is 5K! Why not just use a differential amplifier? You'll get about 20db of gain too.

    54916


    But anyway. One signal is dry and the other is wet from the...
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    Let's wait and see it in the final context. It...

    Let's wait and see it in the final context. It seems that this is just a part of the picture.

    BTW, I'm actually more envious of the drill press.
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    Ah! Okay doke. Done like that Zin is 220 ohms.

    Ah! Okay doke. Done like that Zin is 220 ohms.
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    Please note my revision above. I made a boo...

    Please note my revision above. I made a boo boo...
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    About 820 ohms. Remember the model might be...

    About 820 ohms. Remember the model might be poor....

    PS: Ignore that. I should have AC bypassed the 10k resistor so the DC conditions were changed to be closer the the answer you needed. Zin by...
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    @HH Some observations using the 6111 model...

    @HH

    Some observations using the 6111 model above, I see the input Z as
    2.5K for the circuit shown
    If you AC ground the grid of the second stage the Zin goes down to 600 ohms. Not a surprise...
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