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Recapping an amp: where to start?

Discussion in 'Amps and Cabs [BG]' started by abarson, Apr 9, 2009.


  1. abarson

    abarson

    Nov 6, 2003
    Santa Cruz
    I'm thinking that it may be time to replace the capacitors on my old TubeWorks RT-3300. My assumption is to start with the power supply caps, as you want to have the cleanest power running to the rest of your circuits.
    Does anyone have a good procedure for recapping an amp?
     
  2. Giraffe

    Giraffe Supporting Member

    Nov 6, 2003
    San Diego, California
    I am no amp tech, but I've recently picked up a few '60's and '70's Fenders, and getting them up to speed has been something of an education!

    With amps of that vintage, it seems most prudent to go ahead and replace all of the electrolytics at once. I have one mid-sixties Princeton that will be hitting the bench for at least the third time because I followed the practice of keeping it as original as possible, and just replacing what needed to be replaced for something close to normal operation. This seemed to maximize the number of visits to the tech, and I now think it would be best to get all of the "perishable" components replaced at once.

    "Buy once, cry once." Good luck with your amp!
     
  3. aye replace all the electrolytics and check all the resistors to make sure there atleast 10 - 20% of their original spec!
     
  4. jimbilly

    jimbilly

    Apr 19, 2006
    I've got one of those amps, I didn't think it was all that old, until now...
    My tech does a visual check (I'm learning), and some sort of electronic stress test on the caps, it's usually pretty clear if they're bad or not. What's it doing that makes you suspect the caps are bad?
     
  5. If it's an Point-to-point or turret design, the easiest way is to cut out the caps from their leads, and twist the old leads together with the new leads on the cap. Not as pretty, but it's faster, simpler, and you do not have to mess with any old solder joints.
     
  6. abarson

    abarson

    Nov 6, 2003
    Santa Cruz
    First off, I'm definitely changing out the 12ax7 in the preamp section, but in general the amp is a bit noisier than it was when I bought it. C'mon, it was made in 1993! It's still got plenty of power, but it has sounded better in the past. Any other suggestions?
     
  7. seamonkey

    seamonkey

    Aug 6, 2004
    Get hold of an oscilloscope and probe each section to find where the noise is coming from.
    Maybe do this before you recap.
    Heed all safety warnings and understand the risks of working on live equipment.
     
  8. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Made in '93! The caps should be fine! You shouldn't need a recap until around 25-30 years. You may well HAVE a bad cap but I doubt all of them have failed. As seamonkey suggests, diagnose the problem first. just throwing parts into an amp in the hope of fixing an unknown problem is not too wise, not to mention expensive!

    If you have no knowledge of electronic trouble shooting and repair, as seems obvious from your original question (sorry if I'm wrong), leave this to a tech. It'll be cheaper and safer in the long run.

    Paul
     
  9. Ummm, I'm gonna have to disagree with this recommendation.

    Gary_Cole_in_Office_Space.


    Please don't take this personal, but this is definitely not the proper way to normally replace components. Rather, it's a lazy or unskilled hack.
    Turret, eyelet, or P-T-P terminal strip construction even lends itself to easily de-soldering the old leads or components. It can also be done on printed circuit boards with good technique and proper care.
    If someone is concerned that you do not have to mess with any old solder joints then they shouldn't be inside an amp in the first place.
     
  10. In a word: BAD advice. Components are soldered down for a very good reason(s)... to counter vibration and maximize current flow.. not to mention combating oxidation/corrosion at those 'tie' points. On the places where components are unsoldered, they will need to be very carefully resoldered with good-quality electronics-grade solder. Don't take "short cuts" when dealing with expensive amplifiers and high voltages.
     
  11. abarson

    abarson

    Nov 6, 2003
    Santa Cruz
    Okay, I'll agree that it probably is a lazy approach rather than proper troubleshooting. Maybe I've been trolling the hifi forums too much, and am influenced by their claims of recapping being some kind of holy pursuit or elixir.

    Although the Tubeworks is not point-to-point, but rather a hand-drawn printed circuit board, the advice above about properly desoldering and resoldering rings true, and not just for amps. If you care about what you play through to the point that you own such an amp, you certainly won't take shortcuts in its maintenance.
     
  12. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    Are you using a newer cab than the one you had back then?

    A new cab, with modern drivers, may simply be revealing noise that was always there.
     
  13. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Thank you DaveM and Rattman. I'm not alone in thinking the clip approach is poor workmanship. To me the inside of a amplifier should be virtually a work of art. If it doesn't look good it isn't good. On the other hand I've seen this method recommended time and time again in books and on various forums so I can see where it comes from. A wise man once said, well more than once actually, "Do it right the first time!".

    Paul
     
  14. no reason to solder to the leads ona p2p design. i've done it with diodes on a circuitboard that would require a huge amount of desoldering to get to the back of, but caps are bigger than diodes, and p2p makes things easy to solder properly. some old circuit boards are pretty dodgy and lifting the traces is not difficult to do.
     
  15. abarson

    abarson

    Nov 6, 2003
    Santa Cruz
    Yes, I've got a totally different set of speakers going on. I'm still going to do the rudimentary troubleshooting to make sure all is well in the bass head and in my head.:smug:
     
  16. +1 on this, i hate opening up a second hand amp/pedal and seeing bodge jobs that people have done as you just have to waste time rectifying there laziness
     

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