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    It's a common tweak to lower the bias current....

    It's a common tweak to lower the bias current. Nothing to do with the tube PCB.

    I have two other other versions on Reverb. One is for the early V1 "Green Board" FBJs. The other "premium version"...
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    Aw shucks. Thx :bigsmile:

    Aw shucks. Thx :bigsmile:
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    Should you change your mind there are PCBs...

    Should you change your mind there are PCBs available e.g. https://reverb.com/item/10803881-fender-blues-junior-fbj-cream-board-compatible-replacement-tube-pcb-with-bias-test-points-by-mox
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    I expect these are customer returns that have...

    I expect these are customer returns that have been tested to ensure they are OK. I would say they are as good as new.
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    I have plenty axials 22uF -220uF, 450 to 600V in...

    I have plenty axials 22uF -220uF, 450 to 600V in stock, just pm me if you want some.
  6. In order to diagnose your issue you need to post...

    In order to diagnose your issue you need to post the scope shots as requested. You are just repeating the description that doesn't tell us what we need to know. The Ge diodes should work just as...
  7. With D2 & D5 removed, feed a 100mVpp 1Khz sine...

    With D2 & D5 removed, feed a 100mVpp 1Khz sine into the input. Put scope on DC coupling with 2V/div, Post a photo of the scope display when monitoring Q4 collector.

    Reduce input to 5mVpp and...
  8. You may not be doing anything wrong! With all or...

    You may not be doing anything wrong! With all or one direction set of diodes of diode removed you just have a high gain amplifier. The maximum output signal will be close the battery voltage, about...
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    If that really is a 100uF cap in there it'll be...

    If that really is a 100uF cap in there it'll be leaking far too much current for this high impedance circuit. A 100nF film cap would be more like it.
  10. ...or Faraday suit.

    ...or Faraday suit.
  11. Himm.. I think I'd one of those transducers...

    Himm.. I think I'd one of those transducers might be just the thing to make those pesky intermittent faults show up on so much of the gear I see.
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    The usual reason is because someone connected an...

    The usual reason is because someone connected an input to something they should not have. Where are "2CR?" and "2C4" on the schematic?

    An "arc" would be very unusual. A burn scorch due to over...
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    It's a ten ohm resistor then links the local...

    It's a ten ohm resistor then links the local ground to the chassis.
  14. You'll need to add a DC blocking cap in series...

    You'll need to add a DC blocking cap in series with the feedback resistor on the mixer stage. Since you want heavy local feedback you might as well make the stage have as much gain as possible by...
  15. I had meant to type 1000uF, not 100uf. Try the...

    I had meant to type 1000uF, not 100uf. Try the bigger ones.
  16. I'd focus on those two 100uF caps that filter the...

    I'd focus on those two 100uF caps that filter the input diff amps. If there were a power supply noise rejection issue then that input stage is the sensitive area. Just parallel them with 100uF and...
  17. ***Yikes! That schematic is full of errors :(...

    ***Yikes! That schematic is full of errors :( Suggest you look at what you actually have and feed back a corrected schematic.
    **Scrub that. It's just sheet one that is misleading.

    Turn vol to...
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    Then you have a symbol of the same name but...

    Then you have a symbol of the same name but different shape in your sym lib.
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    Didn't get to that point as there was no symbol...

    Didn't get to that point as there was no symbol for the pot. You will have seen the same problem if you tried to load my version above as I didn't include it. No symbol, so no lib reference.
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    You can just include the model right on the...

    You can just include the model right on the schematic:

    54225
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    You're missing a ground connection. The model...

    You're missing a ground connection. The model for the pot is missing.

    I tried it out but I could not get it to work as drawn. I then first did a plot of Rp vs Vg1 for a 6SN7 with a constant 120v...
  22. Thread: Yamaha EM1600

    by nickb
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    Try Yamaha. They often will give you old stuff...

    Try Yamaha. They often will give you old stuff for no charge. Failing that iI see it can be bought is you search for it. I don't have it though.
  23. Thread: Yamaha EM1600

    by nickb
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    2,361

    54210

    54210
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    I think it's going to have very non linear...

    I think it's going to have very non linear compression, that is to say the peak signal amplitude to attenuation plot is not a straight line. That might be desirable, or course, in some cases.
  25. Another hotly debated subject, for sure. Read MEF...

    Another hotly debated subject, for sure. Read MEF Thread
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    'Please' might be nice. 54167

    'Please' might be nice.

    54167
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    54166

    54166
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    Well spotted. Those are expensive at $30 a pop. ...

    Well spotted. Those are expensive at $30 a pop.

    You can substitute a pair of transistors such as KSC1845 that are inexpensive. For best results super glue them with the flats touching each other.
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