super reverb incredible issue

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by gianluigi, May 13, 2015.

  1. gianluigi

    gianluigi Member

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    I have a15 years old super reverb clone that always served me perfectly.
    it started having intermittent issues with volume drop and distortion ,I tried anything starting from tubes then components ,trying other output transf etc.nothing.so I decided to rebuild it in a single channel configurationis with no tremolo(I don't use it)
    everything seemed fine for a couPle of days than the problem appeared again this time I changed power tubes,fine for 2 days then again sometimes it sounds with more volume than normal sometime it seems ok .the only things that I didn't changed are the transformers but I've already changed the output one.can it be the power transf ? voltages seem ok ,there is nothing left to change.the choke? all the sockets jacks and pots have been changed too,
    NEED HELP
     
  2. jay42

    jay42 Member

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    You'll need very good light, your DVM, and a magnifying glass. You need to figure out if the problem is mechanical or not. Test the tubes in other amps to rule them out. You're looking for cold solder joints first and foremost. Breathe evenly and take your time. hth

    [edit] Look for socket issues...solder splash, arcing residue, loose tube connections.
     
    Last edited: May 13, 2015
  3. gianluigi

    gianluigi Member

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    Ok but it has been rebuilt.it can't have the same issue as before
     
  4. Blue Strat

    Blue Strat Member

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    Can you post a schematic and some photos of the board and wiring? Trying to figure this out without seeing it is like playing darts blindfolded. ;)
     
  5. amphog

    amphog Silver Supporting Member

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    New tubes may not be good tubes.
     
  6. gianluigi

    gianluigi Member

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  7. gianluigi

    gianluigi Member

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  8. Blue Strat

    Blue Strat Member

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  9. gianluigi

    gianluigi Member

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    Everything is ok voltages within specs.no fluctuating voltages.
     
  10. Blue Strat

    Blue Strat Member

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    What's your bias setting? Also, monitor the power tube cathode current when the amp starts having the problems.
     
    Last edited: May 15, 2015
  11. gianluigi

    gianluigi Member

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    what can it be?
     
  12. Steppin' Wolfe

    Steppin' Wolfe Member

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    gianluigi, without knowing the current draw and using that with the plate voltage; it is impossible to know the plate dissipation factor. IT may be that the amp is running very hot and going through tubes quickly. At least, one would want to know these things before going farther into the analysis/diagnosis, ime.
    So....+1 with Blue Strat on the current draw and monitoring during good and bad times.
    Rebuilding and repalcing components without knowing the basic situation/problem is or could be very frustrating and expensive.
     
  13. gianluigi

    gianluigi Member

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    I'll take measurements as soon as I can and I'll report back
    thanks
     
  14. Blue Strat

    Blue Strat Member

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    Also, try setting the idle current to about 30-35mA for now. If you're not sure how to do that, let us know.
     
  15. gianluigi

    gianluigi Member

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    The pin 8 has got a 1 ohm res to ground and the bias is set around 31 ,32 ,mvolts.but if that resistor is not so precise the real bias can be very different from what the dvm says
     
  16. gianluigi

    gianluigi Member

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    I own two other amps built the same way .the only differences are the octal sockets (belton in the amp we're talkin about).
     
  17. Blue Strat

    Blue Strat Member

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    Ok, that's perfect. Now, keep your meter on the bias test point(s) (the 1 ohm resistors) and play the amp. When it starts to misbehave, see if those 31,32 readings change significantly (you'll have to stop playing).

    If any of your ground connections are soldered to the chassis pull on them with a pair of pliers to make sure their solid. Check all other ground connections too.
     
  18. gianluigi

    gianluigi Member

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    The bias stays stable.but I measured the 1 ohm res and in the circuit it reads 1,5 ,ohm .is it normal?.this can change the mV readind.
     
  19. walterw

    walterw Gold Supporting Member

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    i think it's a general rule that you should find and fix the problem with an amp before modding it.
     

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