Problem with amp tremolo

Discussion in 'Shock Brother's DIY Amps' started by mdancakster, Feb 20, 2018.

  1. mdancakster

    mdancakster TDPRI Member

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    Hello there,
    I have a problem with tremolo in my Tremolux. The pulses are really strongly audible (ticking) if the tremolo is engaged/on (even if there´s no signal from the guitar) and I don´t know what´s going on. It´s the tweed 5e9A schematics but I finally changed the paraphase PI for that of tweed deluxe 5e3 because of better overall sound (as in EC Tremolux circuit – cathodyne PI); if the circuit was the original one (5e9A) everything with the tremolo was OK. After changing the PI scheme the problem with tremolo occurred. All the measured voltages values in tremolo are + or - 20% of the original 5e9A schematics. I´ve already tried to change the tremolo valve for another three but nothing changed). Any suggestions? Many thanks. Regards, Martin.

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  2. clintj

    clintj Friend of Leo's

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    There's quite a few differences between the two amps, obviously. Did you do the complete conversion to the EC version, where it drives the power tube grids instead of the screens?

    In any case, thump regardless of setting implies the LFO signal is being picked up somewhere unintended. It's either climbing back through connected circuitry, or being picked up as radiated noise. Do you have pics of what we're dealing with?
     
  3. JuneauMike

    JuneauMike Friend of Leo's

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    Did your component swaps change the bias any?

    If this is a bias vary trem that affects the output tubes, you might try just swapping the tubes to see if it goes away. If they are not matched well to begin with, the variation in bias may have made the thumping noise more pronounced. (If anything, this is a test you can do in about 2 minutes and it won't cost you anything.)
     
  4. dan40

    dan40 Tele-Afflicted Silver Supporter

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    Good lead dress or the use of shielded wire on the oscillator's grid has often helped me to cure the thumping sound in a few of mine.
     
  5. JuneauMike

    JuneauMike Friend of Leo's

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    I really liked this video. Maybe if can help you begin to sort out your problem.


     
  6. JuneauMike

    JuneauMike Friend of Leo's

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    Why did you select 470k on the plates? What does it actually measure? That would lead to the power section, right? Was that when the problem started?

    So you swapped a 2M pot for a 3M pot and adjusted the tail resistor accordingly. What effect did that have?

    I'm sorta trying to understand the care and feeding of these old tremelo circuits too. I liked parts of this article:
    http://www.aikenamps.com/index.php/designing-phase-shift-oscillators-for-tremolo-circuits
     
    Last edited: Feb 26, 2018
  7. JuneauMike

    JuneauMike Friend of Leo's

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    Are you still working the problem?
     
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