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  1. Replies
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    THe 6L6-GC datasheet specifies 5.6k for...

    THe 6L6-GC datasheet specifies 5.6k for Vp=450/Vs=400V. Fender typically used 4.2k but with Vs= 420V or higher. Optimum Rpp depends on Vp and Vs. Lower Vs requires higher Rpp.
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    The way you described your problem, the cause...

    The way you described your problem, the cause must be before the channel mixing point.
  3. Will be lower with the bulb limiter. PT voltage...

    Will be lower with the bulb limiter. PT voltage verification does not work on the bulb limiter.
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    Good point! (My 1967 Marshall JMP100 Tremolo...

    Good point!

    (My 1967 Marshall JMP100 Tremolo puts out exactly 60 clean Watts with 2 Svetlana EL34s and a plate voltage of 474V. Plate voltage drops to 448V at full power.)

    The GE 6L6-GC...
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    This would mean a leakage resistance of around...

    This would mean a leakage resistance of around 2M.

    I recommend to disconnect the wire from either 1A or 1B and measure resistance between 1A and 1B again.




    You described an asymmetrial...
  6. Sorry, this is negative DCV again. What about the...

    Sorry, this is negative DCV again. What about the original positive DCV?

    A little negative DCV is normal. The tube datasheet recommends a 10M grid leak resistor for grid leak biasing. One can...
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    Looks ok except that I would have expected to see...

    Looks ok except that I would have expected to see 2M instead of 1M. Reason is that between 1A and 1B there is a DC path through both vol pots in series. Does your amp have 500k vol pots instead of 1M...
  8. Even without tubes? Do you have a bulb limiter?

    Even without tubes?

    Do you have a bulb limiter?
  9. What about the positive DCV? Can you still...

    What about the positive DCV? Can you still reproduce it?
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    I can't find this remark about G2 and G3. Rather...

    I can't find this remark about G2 and G3. Rather this:

    "Plate power dissipation of EL34-B can reach 30W, whereas EL34A is 25W. EL34-B belongs to tetrode
    tube compared to pentode tude of EL34A. g1...
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    An underrated OT is likely to cause ugly...

    An underrated OT is likely to cause ugly saturation distortion, limit bass transfer and reduce available output power. When saturation occurs OT primary current strongly increases which may shorten...
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    Still the same problem? What are the cable...

    Still the same problem?

    What are the cable defects?
  13. Good point! In fact, the output coupling cap is...

    Good point!
    In fact, the output coupling cap is part of the output impedance of the circuit and output impedance is reduced by the loop gain. So the capacitance should appear to be increased by the...
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    Tube amps don't kill proper speaker cables (might...

    Tube amps don't kill proper speaker cables (might be different if instrument cable is used instead). Analyse the defective cables and find the failure cause.
    Also clean jack(s), cable plugs and...
  15. Now this is confusing as all voltages are now...

    Now this is confusing as all voltages are now negative and inconspicuous regarding level. What does it take to restore the higher positive voltages?

    Again my earlier questions: What changes with a...
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    Seems the facts speak for themselves. And facts...

    Seems the facts speak for themselves. And facts (as opposed to internet rumours) is all I am interested in.
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    That's what I was hinting at.

    That's what I was hinting at.
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    Good question, provided we are speaking of the...

    Good question, provided we are speaking of the same tube.

    The whole story seems obscure to me. I mean, why should a manufacturer give his tetrode the name of a classic pentode? Tetrodes and...
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    So pentode.

    So pentode.
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    It should be possible to tell a pentode from a...

    It should be possible to tell a pentode from a beam tetrode by dissecting a (defective) tube and see if it has beam confining/reflecting plates or a third (suppressor) grid.
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    With 100R it should have a power rating of 0.5W...

    With 100R it should have a power rating of 0.5W or more.
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    4A and 4B are ground (please verify) and are...

    4A and 4B are ground (please verify) and are jumpered, so they will always be shorted. In MINUS position, the switch connects 3B with 4B and 3A with 4A, so all of them will be shorted with each other...
  23. Depends on how much you can load your wet/dry...

    Depends on how much you can load your wet/dry signal sources and how much gain you need. In post 4 I gave an example. The total gain as seen from each source will be roughly given by feedback...
  24. Normal grid leak current is caused by electrons...

    Normal grid leak current is caused by electrons hitting the grid and charging it negative. This is how and why grid leak biasing works.

    Positive grid leak would mean a gassy tube that must be...
  25. Strange. Have you also tried different tubes in...

    Strange. Have you also tried different tubes in V2?
    Does the instrument connected have active electronics? Just excluding the DCV comes via the instrument.
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    I would think of OT core saturation caused by PI...

    I would think of OT core saturation caused by PI signal asymmetry (means net DC in the primary) and low frequency content. Only a (preferably dual channel) scope could tell.
  27. Correct, I missed this path. It was just a...

    Correct, I missed this path.
    It was just a general remark. As shown without coupling caps the grid will see (high) positive voltage.
  28. Is the DC positive or negative wrt ground? I...

    Is the DC positive or negative wrt ground?

    I guess the voltage drops to zero without a plug inserted?
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