Ratty distortion on 70 Deluxe Reverb

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by steveb, Feb 7, 2010.

  1. steveb

    steveb Member

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    Oct 11, 2006
    I have a 70 Deluxe Reverb that I haven't played in a few months & decided to bring it to rehearsal yesterday. I did okay for a hour or so, & then started making a few noises. I switched to another amp for the rest of the rehearsal, but checked the Deluxe later on. The reverb channel of the amp sounds good until about 5, & then starts making a ratty, busted speaker sound as the volume is increased to 9, but then, the nastiness decreases a bit at 10.

    The normal channel does not sound as bad as the reverb channel.
    Tried plugging into another speaker & the nasty sound is still there.
    Tried all different preamp tubes, & the nasty sound is there, too.
    I tightened the power tube sockets, & it made no difference.

    I made a recording, but the nastiness is not as noticable as in person, but you'll hear it. I start off playing with the volume at 4, then increase it a bit during the recording until reaching full volume. Bass & treble on 4.
    http://www.sbkustoms.com/music/amps/70 deluxe reverb.mp3

    The power supply caps were changed before I got the amp, but the rest of the caps look to be original.
     
  2. soldersucker

    soldersucker Member

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    May 20, 2006
    My vote is a bad 25mf cathode bypass cap.
     
  3. TheAmpNerd

    TheAmpNerd Member

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    While you got it apart might as well do 'em all and
    the Power supply electrolytics too.
     
  4. steveb

    steveb Member

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    Thanks.
    I have 3 other Fender amps that I changed all the electrolytics on the circuit board not long after getting them, & it escapes me why I never did this one, too.
     
  5. JJman

    JJman Member

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    Mar 12, 2006
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    New Jersey
    My '71 was doing this recently. I had removed the anti-oscillation grid-to-ground caps from the 6v6 tubes previously. So I changed their grid wires to shielded and the problem went away. Same story on my '74 VC.
     

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