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  1. Replies
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    I'm glad that you are reanimate an old man. He...

    I'm glad that you are reanimate an old man.
    He deserves to be gladden with new tubes.
    Now take the guitar in your hands and 55671
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    FBT is absolutely silent, when you play (the...

    FBT is absolutely silent, when you play (the previous clip) sounds solid.
    All the audible sensations which you hear when the guitar is plugged in are normal because the PU detects all EM radiation...
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    You have not overreacted, but you expect too much...

    You have not overreacted, but you expect too much from the old man.
    Can you record an audio clip with the amp on without a guitar, let's hear what's really going on.
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    Your amplifier is a music amplifier, it's not a...

    Your amplifier is a music amplifier, it's not a HiFi amplifier.
    The best way to see if an amplifier is working properly is to compare it (one to one) with another amp of the same model. (FBT 200 to...
  5. Is the earthing from the wall to the mains cable...

    Is the earthing from the wall to the mains cable correct
    Does exist noise when the guitar is plugged into the amplifier:
    - when the volume on the guitar is at max (10)
    - when the volume on the...
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    PT transfer own vibration to the chassis, and...

    PT transfer own vibration to the chassis, and this vibration via tubes socket transfer to the tubes.

    It happens over time that the electrodes in the (old) tube slightly mechanical relax , and some...
  7. Good news Marshall half-worked. Since clean ch...

    Good news Marshall half-worked.
    Since clean ch sounds really really loud, we don't need to test the power amp. If the power amp works properly on clean ch fault is in dirty ch.
    For this repair do...
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    Same story turns around over 100 posts, and we...

    Same story turns around over 100 posts, and we still don't know what Fender signal test voltages are.
    ...
  9. Since the bias voltage is insufficient because...

    Since the bias voltage is insufficient because the quiet current is still large, it may be possible to increase the trim pot from 25 kOhm to 50 kOhm.
  10. For your plate voltage 455V ClassAB Ia = 44 mA ...

    For your plate voltage 455V
    ClassAB Ia = 44 mA
    High AB Ia = 58 mA
    If you measuring current at the cathode, besides anode current you should have added current Ig2 (5 - 10% Ia)
    ...
  11. Where we left off with Marshall?

    Where we left off with Marshall?
  12. What does not connect in series 150 KOhm and 68...

    What does not connect in series 150 KOhm and 68 KOhm so with mini switch have a choice 150 KOhm or 220 kOhm

    55614
  13. Replies
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    Krank schematics

    https://guitar-gear.ru/forum/topic/1491-krank-krankenstein/

    https://el34world.com/Forum/index.php?topic=15354.0

    https://www.diyaudio.com/forums/instruments-and-amps/85870-krank-circuits.html
    ...
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    Before testing, soldering elco contacts or clean...

    Before testing, soldering elco contacts or clean from the oxide.
    When testing cathode elco unsolder cathode resistor from elco
  15. For the 6550, the cathode and screen g3 are...

    For the 6550, the cathode and screen g3 are connected in the tube itself and executed at pin 8.
    To adjust the quiet current connect a 1 Ohm resistor from pin 8 to the chassics.
    Pin 1 is neutral (N...
  16. Pin 8 is cathode and must be grounded. Screen g3...

    Pin 8 is cathode and must be grounded.
    Screen g3 in some tubes is connected to the cathode in the tube itself, or as EL34 derived as a separate electrode that must be grounded.
    Look at layouts...
  17. Basically at octal power tubes except 7027 and...

    Basically at octal power tubes except 7027 and EL34 pin 1 is no connected and is used for various purposes.
    At EL34 pin 1 (screen g3) must be connected with pin 8 (cathode)
    7027 has a different pin...
  18. When measurement the cathode current, in addition...

    When measurement the cathode current, in addition the anode current, screen current g2 also enters.
    Measuring by the OT resistance is perhaps the more reliable variant since only the anode current...
  19. Quiet current or calm current or idle current is...

    Quiet current or calm current or idle current is defined by bias voltage.
    One tube don't damage OT.
    When adjusting the bias, the loudspeaker must be connected to the amplifier.
  20. When you set the quiet current with one tube, you...

    When you set the quiet current with one tube, you can normally put another tube.
    It goes without saying that the tubes are relatively matched.
    With only one tube in the socket you can measure and...
  21. To start, put one tube 6550 in socket. ...

    To start, put one tube 6550 in socket.
    Previously with the bias trim pot set to the highest -Ug1 value (- 55 V min), put one 6550 and gradually decrease the -Ug1 to set the quiet current to the...
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    The voltages on V2 and V4 are fine.

    The voltages on V2 and V4 are fine.
  23. Replies
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    If volume and tone controls not work at anode V2...

    If volume and tone controls not work at anode V2 (pin 6) check capacitor connection .1uF; .022 uF and 250 pF with tone control pots.
    Check the anode and cathode voltages on tube socket V2.
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    https://www.scribd.com/document/369047600/MXR-117-...

    https://www.scribd.com/document/369047600/MXR-117-Flanger-Service-Schematic

    https://drive.google.com/file/d/1vpHJanRoGtZgz-OA0p3wA4mDucRT0-ca
    ...
  25. The value of the bias voltage depends solely on...

    The value of the bias voltage depends solely on the bias voltage divider (15 kOhm) according to (56 kOhm + 22 kOhm bias trim pot)
    Bias feed resistors (100 - 220 kOhm) and grid leaks resistors (1.5...
  26. About biasing tube guitar amplifiers

    https://music-electronics-forum.com/showthread.php?t=8291

    Bias adjusts depending on the + HV and working classes of service (A, AB, B) to the specified anode current value.
    ...
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    Since sound sensations do not exist when the head...

    Since sound sensations do not exist when the head is separated from the cab, the cause should be sought in the head.
    In the background when you're not playing there is a modulated sound like a...
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    With a gentle knock with finger on the output...

    With a gentle knock with finger on the output tubes check if there are any audible sensations.
    If the output tubes worked for a long time, the electrodes in them move slightly (usually in rhythm of...
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