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Fender PA 100 to Twin Reverb convertion

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  • Fender PA 100 to Twin Reverb convertion

    Hello everybody I'm kind of a beginner in electronics(made a few stompboxes).I bought this amp(fender PA 100) about 7 years ago and intended to work on it but sorta put it on the backburner.Anyway I have recently vowed to actually finish it now.I have looked at the amp and found out it would actually be a good amp to turn into a twin reverb.Here are a few things that the amp is similar to the twin reverb :
    Power transformer
    output transformer
    choke
    reverb transformer
    all the valve tubes (4 6L6's and 1 =12ax7 2+12AT7 and 3 7025
    All I basically have t do is put the right circuit board on there and the pots and I think that should be it(I thinK)

    And now to my question.I want to save as much of the other capacitors as I can from the PA cause I dont want to spend too much if I dont have to.My question is that the filter caps on the PA are 2 caps of 100MFD 350Volts and 3 caps of 20MFD at 500Volts.On the otherhand the schematics for the AB763 twin reverb is 2 caps of 70 MFD at 350 volts and 3 caps of 20MFD at 525 volts.The question is can I use the existing caps on the PA in place of the AB763 values.Also how do I make sure that the caps are still good.Sorry about the long intro I just want to be thorough.any help would be appreciated
    Last edited by bluesmojo; 08-10-2007, 11:43 AM. Reason: posted before i was actually finished

  • #2
    If you're rebuilding an amp, you probably ought to replace all of the electrolytic capacitors while you're in there. If you want to save money, use the cheap no-brand ones instead of Sprague Atoms.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    • #3
      Thanks for the reply steve.I did went ahead and replaced the caps on the board with orange drop capacitors.The filter caps considering that they are a bit pricey.I wanted to know if the capacitors are values I could use for the twin reverb project.Steve I am now in the process of installing eyelets on the board for the new circuit.I used the bottom board and will remove the eyelets form the original PA board and put that on the bottom.I'll keep you posted on the build!Thanks

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      • #4
        By electrolytic caps, I meant the filter caps. They are the most important ones to replace, since they are known to degrade after about 10 years. The other caps (that you already replaced with orange drops) don't actually need replacing unless they go bad. Unless they were paper-in-oil types instead of plastic film.

        Sure, the values are close enough to use in your Twin Reverb build (ever seen the tolerances on electrolytics? many are -20%, +80%) but you really are better throwing them away and getting new ones.
        "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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        • #5
          Oh thanks for that reply Steve.That is really helpful.I like the look of the orange drop caps anyway so I'm still glad I bought them.maybe I will go ahead and replace that if I find the right values from my local electronic store.My local electronic store found a supplier for carbon comp resistors too.So I would now be able to get the values I need.Thanks again for your help steve I'll keep you posted>

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