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Thread: Fender Twin Reverb - Massive Farting Sounds!

  1. #1
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    Fender Twin Reverb - Massive Farting Sounds!

    OK guys...

    I have a Twin (1979 SF - 135W) that sounds OK at low volume levels, but when it gets up around mid way it makes a disturbing fart noise that sounds like an overdriven tuba.

    Amp has all new tubes. I checked them in my Super Reverb, all OK.

    Speakers are good. Checked on Super Reverb.

    I checked all the voltages against schematic and they are OK. The bias is OK around 41mA per tube.

    I looked for DCV on the signal side of all the coupling caps.

    I changed the filter caps.

    I re-flowed, over time, every solder joint on the eyelet board and the tube sockets.

    I tried lower gain preamp tubes (12AU and AY).

    A friend suggested possibly blocking distortion, but I am relatively new to this game and didn't really absorb what I was reading.

    At my wits end and would appreciate any help you guys can offer...

    Thanks,
    Mike

    http://schematicheaven.com/fenderamp..._135_schem.pdf

  2. #2
    Forum Member curtisstetka's Avatar
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    Re: Fender Twin Reverb - Massive Farting Sounds!

    Did the amp sound okay for a period of time and then it started farting? If so, did the farting come in gradually or suddenly?
    s'all goof.

  3. #3
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    Re: Fender Twin Reverb - Massive Farting Sounds!

    This amp came to me this way. The owner has brought to two techs that have BS'd him into buying a new speaker and a new set of tubes.

    If it helps... The problem IS common to the normal and tremolo channels which makes me think maybe its further down the line like maybe the next gain stage or the PI. The reverb or trem controls have any affect and the problem exists with both completely cut.

    I think its probably a coupling cap, but I am not a well equipped shop with a cache of spares hanging around. I hate to order $20-30 on a hunch. But then again maybe thats how I'll get that cache of spares:)

  4. #4
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    Re: Fender Twin Reverb - Massive Farting Sounds!

    four things or a combination of any of these three could be happening.
    1) arcing output tube socket, look for burned pitting form pin to pin on the socket.
    2) burned or some what bruned grid resistor on the output tube socket(s). On these latter amps the wireing is souch a mess that some times you can even see them, so double check them.
    3) Shorted output transformer whos demise may have been assisted by any of the three things above.
    4) Power supply caps going bad, if they are original its high time they where changed out!

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