Deluxe Reverb Power Capacitor Question?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by teleman55, Feb 19, 2015.

  1. teleman55

    teleman55 Member

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    Can an amp still kind of function with one disconnected power cap??? My silverface DR seemed to have lost a bit of luster of late. Still functioned fine, no excess noise, etc. Just was like it lost a step. Tried different tubes, etc. So I have been using something else with band of late. But did use it Saturday night. Worked OK but same thing. So I just decided to open it up. This thing got re-capped, etc. about 7 years ago but has had a lot of use so thought I'd check. All seems OK inside. But I took the doghouse thing off and lo and behold, the power cap furthest from the rectifier tube was no longer connected at the neg. end. Could the amp function like this??? Or maybe the house was holding it down enough for marginal connection? Got it all discharged so gonna solder it back. But I gotta wonder why it worked at all. And if so, was that the problem. Any insight would be helpful. Thanks.
     
  2. WaltC

    WaltC Member

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    That's the stage farthest down the line of filter caps where, relatively speaking, the filtration is doing the least work on the most filtered part of the B+ rail, so, yes it could easily work with that cap "undone".
     
  3. Blue Strat

    Blue Strat Member

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    What Walt said. Are you noticing any increase in hum?
     
  4. teleman55

    teleman55 Member

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    Thank guys. No increase in hum really. So if it could easily work with that cap "undone" could that be a likely cause of the amp seeming to work fine but just loose a little something that's almost too subtle a difference to describe but you know is there?
    Fixed it last night but too late try it out, so gonna do that now.
     
  5. EpiglottisDynasty

    EpiglottisDynasty Member

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    A bad or disconnected filter cap on the preamp stage will usually inject in a bunch of ghost notes. It is most noticeable on higher notes, and at higher gain levels. When it is really bad, it will sound like someone is playing along with you, but terribly out of tune.

    A DR has, I think 3 cap stages and a choke ahead of the preamp cap, so cutting that cap won't add too much hum, and it won't ghost note as badly as most amps would. I had an amp where the pre-stage cap was only one resistor off the transformer, and when it came loose, every note sounded like a dissonant chord and every chord sounded something like this.
     
  6. zenas

    zenas Member

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    E.D. I listened to your bad amp sound link. Glad you got that fixed! :)
     
  7. Bruce Gerard

    Bruce Gerard Member

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    99% of the time these get new caps, the person doing it does not put a new chunk of weatherstrip foam in the ceiling of the capacitor tank. Unless you put a new chunk of foam rubber in there, the caps will eventually break off. You can also glue the caps to the eyelet board with silicone - but using the old weatherstrip material is the cleanest most authentic way to go. You can get the stuff at some hardware stores and many auto repair parts stores. It is sold as door weatherstrip - closed cell foam.
     
  8. teleman55

    teleman55 Member

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    Thanks. The old weatherstrip most likely put in when it was recapped about 7 or 8 years ago was still fine. I soldered the cap back. Amp has it's mojo back.
     
  9. pdf64

    pdf64 Member

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    I think that the ghost note thing is more usually due to poor B+ smoothing at the plate or screen grid B+ nodes of P-P amps, due to high levels of 120Hz in the B+ modulating the signal.
    Agree that by pre amp B+ node, there's little need for smoothing; rather the key function may be decoupling, ie prevention of feedback paths (positive and negative) between stages being created via the B+.

    Are you able to verify that the strip is actually pressing on the newer caps? Rather than the original (maybe larger) caps having permanently compressed the strip, so that it isn't actually supporting the newer caps.
     
  10. teleman55

    teleman55 Member

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    Yeah, the strip looks like it went in when this was recapped in 2007 or so. Definitely no some old original stuff from the 70's.
     

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