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  1. Replies
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    6.8K from post #11. Cathode and plate voltage are...

    6.8K from post #11. Cathode and plate voltage are consistent, so I don't suspect cathode resistance.
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    So finally we have all relevant V1/V2 voltages....

    So finally we have all relevant V1/V2 voltages. They look good except for the first triode of V1, which has 30% increased plate current. Is R2 (5.6M) ok and correctly connected?



    What does...
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    The method I am proposing requires to know the...

    The method I am proposing requires to know the orientations of the coilformers/center legs. The centerline through the coilformer defines the (main) magnetic axis. I suggest to orient the...
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    Positioning the laminations of PT and OT at right...

    Positioning the laminations of PT and OT at right angles is a good rule. But there are (at least in theory ) different ways to achieve this. The best orientatation is with laminations at right angles...
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    Feedback requires gain. The more gain the more...

    Feedback requires gain. The more gain the more likely is (unwanted) oscillation. The "2203/2204" channel can be assumed to have way more gain than the other channel, so no surprise here. Actually I...
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    Seems the "L-pad" (actually a simple power pot)...

    Seems the "L-pad" (actually a simple power pot) is not properly grounded.
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    I would start with checking all ground...

    I would start with checking all ground connections with an Ohmmeter. Should measure below 0.5 Ohm with a calibrated meter.
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    The attenuator might have lost a ground...

    The attenuator might have lost a ground connection. But how could we really know without seeing what's inside the attenuator or having a schematic?
  9. I don't know how the BBE Sonic Maximizer works...

    I don't know how the BBE Sonic Maximizer works but the speed of sound does not change with frequency.
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    At the moment I am only interested in V1/V2...

    At the moment I am only interested in V1/V2 voltages.

    I assume these:
    V1 12ax7 228v
    V2 12ax7 228v
    are pin 1 voltages? Please always specify pin numbers as each tube has 2 plates and 2 cathodes....
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    No, channels are not completely independent. In...

    No, channels are not completely independent. In fact the plates (pins 1) of the respective second triodes of V1 and V2 are connected and share a common plate resistor (R13). Consequently these plate...
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    I think model YJC with the ground wire and...

    I think model YJC with the ground wire and (probably) voltage reduction would be the best choice. Will reduce power, though.
    Ground wire shorts the existing cathode resistor.
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    Do you have any idea which of the many Yellow...

    Do you have any idea which of the many Yellow Jackets converters this refers to? I understand that some of them reduce plate and screen voltage while others don't.
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    Is the amp in original condition (no mods)? ...

    Is the amp in original condition (no mods)?

    What is the common plate voltage at V1/V2 pins 1? (This is the point where both channels are mixed and could possibly interact.)

    What happens/changes...
  15. Such behaviour is common to many component...

    Such behaviour is common to many component (including transformer) and contact failures and doesn't prove anything.
    I am not saying that it is likely that a transformer is defective but if so, it...
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    Check cathode voltages (pin 3) of V1 and V2. Do...

    Check cathode voltages (pin 3) of V1 and V2. Do these change with vol settings?
  17. First thing I'd do is check if PT and OT are ok,...

    First thing I'd do is check if PT and OT are ok, as these are the most expensive/valuable parts.
    Amp could easily be converted to a Dual Showman Reverb or Bassman 135.
    ...
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    To me it is not clear up to now what kind of...

    To me it is not clear up to now what kind of "feedback" you have. Could be acoustical (meaning feedback between speaker and PU or a microphonic tube) or purely electrical. How does it manifest/sound?...
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    Yes, it's descibed here:...

    Yes, it's descibed here: https://www.yellowjacketstc.com/detailed-information
    Many different versions.
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    Good observation. I also think that the black...

    Good observation. I also think that the black lead is used to short-circuit any existing cathode resistor and use the internal resistor for biasing instead. This would allow for better center biasing.
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    Yes it will raise plate voltage. But the tube...

    Yes it will raise plate voltage. But the tube only cares about/sees plate voltage minus cathode voltage, so...
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    ??? Why not VC? I mentioned this aspect as...

    ??? Why not VC?



    I mentioned this aspect as the Yellow Jacket leaflet says "converts from class AB to class A operation", which does not hold for the VC.



    This makes the tube run very...
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    Sorry, but what is VB and what is biasing down?

    Sorry, but what is VB and what is biasing down?
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    This might be a misunderstanding. My general...

    This might be a misunderstanding. My general remark above was about converting class AB designs to class A, which must decrease output power as losses significantly increase.

    But the Vibro Champ...
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    I guess it will safely work in a BF Vibro Champ...

    I guess it will safely work in a BF Vibro Champ (already operating in class A) having supply voltages like this:
    ...
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    Maybe this helps: For the tube only the...

    Maybe this helps:

    For the tube only the voltage between grid and cathode matters, consisting of DC bias and AC signal.
    The grid leak resistance always should be smaller than the internal grid...
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    Sorry, not clear what you mean (double language...

    Sorry, not clear what you mean (double language barrier). Maybe you give an example.
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    Cable thickness does not matter.

    Cable thickness does not matter.
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