Which filter caps for a '66 Twin Reverb?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Heritage, Mar 17, 2003.


  1. Heritage

    Heritage Gold Supporting Member

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    I just changed them out about 2 weeks ago but I don't know if the info I read on the net was right or not. I just really started thinking about it right now.
    Also, what else besides the capacitors in the can should I change?

    Thanks,
    Scott
     
  2. VaughnC

    VaughnC Supporting Member

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    Most of the one's I've worked on had three 20uf/500v & two 70uf/350v in the hv power supply.

    You should also replace the bias supply cap which is probably a 50uf/70v.

    And, if you feel real ambitious, it wouldn't hurt to replace all of the preamp cathode bypass caps. They're probably dual pack 25uf/25v, but can be replaced with 2 individual caps of the same value or one's with higher voltage rating.
     
  3. Heritage

    Heritage Gold Supporting Member

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    Thanks for the reply VaughnC.
    When I replaced the filter caps I used 3 20uf's and 2 100uf's.
    Did they originally use 70uf's?
    What brand caps do you recommend using for the preamp cathode bypass caps?

    Thanks,
    Scott
     
  4. VaughnC

    VaughnC Supporting Member

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    Yup, that's what my schematics say. 80uf is probably the closest you'll come these days but they are in tolerance. Theoretically, 100uf could change the feel of the amp but that could be a good thing too.

    As far as the preamp cathode bypass caps, as long as you stay away from the cheap one's you'll probably be ok. Mallory or Sprague should be fine.
     
  5. oldepicker

    oldepicker Guest

    Scott,
    Vaughn is right on. The list he gave of the power supply electrolytics, bias supply cap and cathode caps is what I usually do to an old warhorse when I get it. He's also correct about the value changes with the 70uf cap. In essence, going up in value, voltage rating, and tolerance will usually change the sound of the amp slightly. But, as he said, it may be for the better. I tend to like my Pro Reverbs with the higher values as it tends to clean up and produce better bass response. The Pro is a blackface that tends to break up sooner than others in the line (twins, bassmans and supers as examples). It's got the Vibroverb output tranny and a mod is to swap in the bassman style tranny to tighten things up. Sometimes I'll change some of the interstage coupling caps to better quality than the disc ones, just to feel better, since I'm in there already doing the others.One variation I haven't tried yet is to forego the usual Sprague Atom "Blue Can" caps for some high quality (small tolerance percentage) Black Gate or Solen fast caps just to see what, if any, difference it may make in the sound. Anybody done that out there?
     

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