Left Chanel out, dynaco pas3

Discussion in 'Tube Audio' started by Jacques_579, Jan 12, 2019.

  1. Jacques_579

    Jacques_579 Member

    Messages:
    85
    hi guys,

    Been working on recapping a dyna pas3. For now, I’ve changed the power supply and bypass the tone controls and the loudness tap. I’ve changed the multi selector switch,and kept the original volume and balance tap. Now when I power it up all tube light up ok but no sound is coming from the left channel, I rolled the tube but still no sound. Do you guys have any idea as to why?

    Thanks
    Fred
     

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  2. peterh

    peterh AK Subscriber Subscriber

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    Yes. You messed with it !
     
  3. Jacques_579

    Jacques_579 Member

    Messages:
    85
    So I should of all left everything original and wait for it to die before changing anything?
     
  4. kvflyer

    kvflyer AK Subscriber Subscriber

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    I think you just were being messed with!

    Seriously, if you have a schematic, you can try to follow the signal and see where it stops. If you have test equipment, oscilloscope and/or signal generator you can visually trace the circuit. If not, take a capacitor and hold one lead. Touch the other lead on the grids of the tubes and work your way back toward the input. When the signal stops, you know which circuit has the issue.

    Does that make any sense?
     
  5. 8xlaxx

    8xlaxx It's all ball bearings nowadays. Subscriber

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    A little more back history about your preamp would be most helpful. Was it functioning properly prior to your mods, selector switch swap, etc? Was it completely stock before you recapped and changed out the power supply?

    Most of the Dynaco purists here would recommend putting it back to stock form first, then modifying AFTER you give it a good audition.
     
  6. Jacques_579

    Jacques_579 Member

    Messages:
    85
    I don’t have any oscilloscope but have a voltmeter, the grids is pin 2 and 7 is that what u mean? And if yes do I measure it with tube in or out?
     

     

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  7. Jacques_579

    Jacques_579 Member

    Messages:
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    It was working and I just wanted to give it a little fresh look. I didn’t wanted to modify it too much too and I’ve read that the switch might not been the best, so I’ve changed it. But the rest is pretty much like stock but with new componenent
     
  8. heyraz

    heyraz AK Subscriber Subscriber

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    Check for a cold solder joint.
     
  9. Jacques_579

    Jacques_579 Member

    Messages:
    85
    I checked them all and they all seems ok, I resolder two that looked suspicious but nothing changed
     
  10. ConradH

    ConradH Addicted Member

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    When all you've got is a meter, try comparing voltages between the two channels. Make a nice copy of the schematic and write down the DC voltages (to ground) for all the critical points. Chances are something will be different. If it isn't, you probably have some break in the signal path.
     
  11. knockbill

    knockbill Addicted Member

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    Selector switches are pretty complicated, unless it was an exact replica it would be pretty easy to mix up the leads/parts on it... I would be looking at teh switch wiring very closely, after confirming all the original changes match the schematic... Worst case,,, put the original switch back in, and follow the schem to get back to square one...
     
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  12. peterh

    peterh AK Subscriber Subscriber

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    Yes. It would still have worked.
     
  13. 8xlaxx

    8xlaxx It's all ball bearings nowadays. Subscriber

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    @knockbill is right. From your pic it looks like you swapped this switch in:

    [​IMG]

    Re-install the stock switch per schematic. Even though the stock switch gets 'soft' (not a firm click) it probably just needs a quick shot of D5 or F5 FaderLube to get the contacts reinvigorated.
     
  14. 8xlaxx

    8xlaxx It's all ball bearings nowadays. Subscriber

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    @peterh

    Looks like the newer caps (installed above...Panasonics or Sprague Orange Drops,...maybe?, can't really tell) are taking up a ton of real estate on the board.

    If the originals were out of spec, which ones would you recommend? Just curious. No intentions here of hijacking the OPs thread. Just a question,... Thx
     
  15. petercapo

    petercapo Super Member

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    Is the left channel out for all of the inputs or only certain ones?
     
  16. primosounds

    primosounds Powered with pure tube sounds. Subscriber

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    If all you changed was the switch then definitely your problem is in how you wired it up or something like that.
     

     

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  17. s-petersen

    s-petersen Scott Subscriber

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    The first thing i would do is connect the pre to a cheap set of speakers and amp, and touch the center terminals of the volume control with just a test lead, if the tubes and power supply are correct, it will buzz in each channel.
     
  18. Jacques_579

    Jacques_579 Member

    Messages:
    85
    Out for all of the input
     
  19. Jacques_579

    Jacques_579 Member

    Messages:
    85
    I just try this and it’s not buzzing at all. Do you mean inside the amp where the wires are or on the front where is the volume knob?
     
  20. Jacques_579

    Jacques_579 Member

    Messages:
    85
    Ok I’m pretty noobs when it comes to this. First; do I put in when doing so and with power on it yes?
     

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