super reverb single channel reverb no tremolo new build

Discussion in 'Amp Tech Center' started by gianluigi, Sep 20, 2019.

  1. gianluigi

    gianluigi TDPRI Member

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    I just finished a new build ,a single channel super reverb with no tremolo
    the amp sounds clean but too much bright just like having a super bright switch engaged
    I changed cabinet
    reverb tank
    reverb cables
    guitar
    guitar cable
    4 different sets of power tubes
    too many pre amp tubes
    all voltages are ok
    checked the electrolytics with a capacitor tester
    no noise is present
    sometimes changing a tube seems to tame the treble but issue appears next time I switch on the amp
    double checked all resistors value
    the sound is metallic and you can notice it better playing the bridge/ middle position on a strat
    two techs tried to see if something is goin' on on a scope.and both of them told there's nothing wrong
    please need help
    thank you in advance
     
  2. Mexitele Blues

    Mexitele Blues Tele-Holic

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    What happens when you turn the treble knob? Are the speakers broken in?
     
  3. gianluigi

    gianluigi TDPRI Member

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    even with the treble low the metallic highs are present .it's a kind of out of phase thin sound ,metallic ,unpleasant
     
  4. schmee

    schmee Poster Extraordinaire

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    Do you have a layout we can see? If single channel you need to change one resistor, but really, I dont think that is your issue. Are all your ground points on the top of the board grounded? Trace and retrace your wiring.
    It's the 1500 ohm shown in this layout near the D location, it was 820 ohm on the dual channel.
    [​IMG]
     
  5. Mexitele Blues

    Mexitele Blues Tele-Holic

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    Is it possible you wired the treble pot as a variable resistor (like the Bass knob) instead of a potentiometer?
     
  6. gianluigi

    gianluigi TDPRI Member

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    IMG_20190920_172351.jpg IMG_20190920_172359.jpg IMG_20190920_172406.jpg IMG_20190920_172410.jpg IMG_20190920_172419.jpg IMG_20190920_172430.jpg
     
  7. FenderLover

    FenderLover Friend of Leo's

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    Maybe check your coupling cap values carefully. You may have neutered the bass completely and all you have left are highs. Do you have bass response with the bass knob?
     
  8. gianluigi

    gianluigi TDPRI Member

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    I think I found it!!!
    could it be the pilot lamp holder that was completly loose ?
    it should be a bad ground issue
     
  9. Wally

    Wally Telefied Ad Free Member

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    Tighten that pilot lamp nut. Did that fix the problem? I doubt it.
    Have you made a voltage chart? Did the tech who put a ‘scope on the circuit do any voltage checks? The voltages may well be correct, a chart should be done in all cases, imho.
    I feel your problem is in the tone stack...as Fender Lover points out. Perhaps you could lift the tone stack and see what the amp does with it out of the circuit?
     
  10. gianluigi

    gianluigi TDPRI Member

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    this is what happened after tightening
    it's not the first time to me,years ago I had an amp with intermittent issue thin and dirty ,thin and clean,loud ,and it was a loose pot
     
  11. Wally

    Wally Telefied Ad Free Member

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    Tightening a pot to make good ground is a different thing than tightening the pilot lamp, ime. That said, it needs to be tightened; and if the amp comes to life with ONLY the tightening of that nut, then I will take that under advisement. Did you tighten it?
     
  12. gianluigi

    gianluigi TDPRI Member

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    This is what I did and thi is what happened...

    Inviato dal mio LLD-L31 utilizzando Tapatalk
     
  13. Wally

    Wally Telefied Ad Free Member

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    My apologies. Your English is far superior to my Italian, but I don’t do taptalk. Did you tighten the pilot lamp nut? If so, did your amp
    Start to work properly?
     
  14. gianluigi

    gianluigi TDPRI Member

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    Sorry.. I dont understand perfectly what you re saying... I don't do taptalk...
    Yes I tightened the nut and the amp started working properly
     
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  15. Wally

    Wally Telefied Ad Free Member

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    Thank you, Gina Carlo. The taptalk reference was to the “Inviato dal IMO LLD-L31 utilizzando tapatalk”.
    Good find on the problem.
     
  16. robrob

    robrob Poster Extraordinaire Ad Free Member

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    For a single channel AB763 if you don't add a "normal channel load" resistor to simulate the load the other channel places on the vibrato channel you'll have a lot more preamp gain than a real AB763. See the Blackvibe schematic and layout for how I did it.
     
  17. gianluigi

    gianluigi TDPRI Member

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    thanks Rob ,your suggestion helped a lot but I found out that cleaning the tubes pins made the amp sound perfectly.
    what do you think about it?
     
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