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Cap/can Question

Discussion in 'Amp Tech Center' started by BeegReeg, Dec 2, 2018.

  1. BeegReeg

    BeegReeg TDPRI Member

    23
    Jun 29, 2017
    Hawaii
    I have a late ‘70’s Princeton Reverb. I just installed cap-can #3 over a period of about 10 years. I gig at least once a week where the amp is on for 3+ hours and use it intermittently at home. When it has gone bad it will start hissing and belching, whether a guitar is plugged in or not. If I thump the cap-can with my finger it will stop for a while-sometimes days or weeks, but progressively get worse. When I put the new cap-can in it runs perfectly for a few years, then starts acting up again. I have swapped out tubes and cleaned connections. I’m wondering if some other component might be going bad, putting extra stress on the caps, or if there are other caps that should be replaced as well when I replace the can. I also have a Vibrolux that just keeps chugging along. Never seems to need attention- but I’d rather tote the Princeton.
     
  2. aerhed

    aerhed Tele-Afflicted

    Age:
    59
    Dec 24, 2016
    Boulder, WY
    Are you doing the cans yourself? What's the voltage rating on your last can (for starters).
     
  3. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    Could be a bad/loose/dirty tube socket; you could try retensioning them.
    Also, I would make sure to replace *all* electrolytic caps that you haven’t already done, like the smaller bypass caps and any others. It’s 40+ years old.
     
    BeegReeg likes this.
  4. BobbyZ

    BobbyZ Doctor of Teleocity

    Jan 12, 2011
    Snellman MN
    What cans are you using?
    Brand and specs.
     
  5. BeegReeg

    BeegReeg TDPRI Member

    23
    Jun 29, 2017
    Hawaii
    It’s the one from Antique Electronics. CE Mfg 4x20 @ 475. I did the first & last. Had a pro do the middle one.
     
  6. BeegReeg

    BeegReeg TDPRI Member

    23
    Jun 29, 2017
    Hawaii
    It’s the one from Antique Electronics. CE Mfg 4x20 @ 475. I did the first & last. Had a pro do the middle one.
     
  7. BeegReeg

    BeegReeg TDPRI Member

    23
    Jun 29, 2017
    Hawaii
    I did clean w/Deoxit & tighten. Haven’t replaced any other caps, tho. Thanks.
     
    RLee77 likes this.
  8. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    I have not witnessed failure of those CE cap cans at that rate...in fact, I have never seen one that I installed fail...and that is over a period more than twice as long as your problems of 10 years. Such a situation would make me want to take very careful note of the wiring and operation of the amp.
     
    Andy B, BobbyZ and D'tar like this.
  9. schmee

    schmee Friend of Leo's

    Jun 2, 2003
    northwest
    I had one CE bad right when new. But I would think if it was good to start, it would last. You are soldering the can to the chassis right?
     
  10. BeegReeg

    BeegReeg TDPRI Member

    23
    Jun 29, 2017
    Hawaii
    Thanks. Makes sense.
     
  11. BobbyZ

    BobbyZ Doctor of Teleocity

    Jan 12, 2011
    Snellman MN
    I've yet to have a CE can fail as well. Thought maybe you were buying NOS caps off Ebay or something, those failing wouldn't be a surprise.
    I've read about bad CE caps on line, but that seems pretty isolated.
     
  12. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    If we are talking about the same cap can failing about every three years, the conditions that might cause e-caps to fail quickly are (a) persistant over-voltage by around 20% or so; (b) getting subjected to high AC voltage/current (as in, the rectifier is failing); (c) very high heat (which the previous conditions mentioned would likely cause).

    "Thumping" the cap and having it then start working better is not consistent with it failing electrically... that sounds more like a bad connection, like an oxidized ground connection or something... moving it causes it to reconnect for a period of time.

    If you can feel the temp of the cap after it has been on for awhile, you could tell if it was excessively hot. You should easily be able to hold your fingers on the cap without being burned.
     
  13. BeegReeg

    BeegReeg TDPRI Member

    23
    Jun 29, 2017
    Hawaii
    I think so. I have a big iron for that kind if work. Thanks.
     
  14. BeegReeg

    BeegReeg TDPRI Member

    23
    Jun 29, 2017
    Hawaii
    Thanks. When you say rectifier, do you mean rectifier tube, or some other component? I have a new JJ rectifier tube, as well as new JJ 6V6’s. Will keep at it....
     
  15. flyswatter

    flyswatter Friend of Leo's

    Jan 12, 2013
    Quebec
    Often when you thump on one component it is not actually the component itself that is the problem, but some other intermittent connection -- such as a cold or broken solder joint -- that is connecting/ disconnecting through vibrations in the chassis.

    Tapping a can cap might for instance be exposing a bad connection elsewhere in the power supply.

    If you are comfortable working in live circuits (if not, take the amp to a tech), chopsticking the connections might locate the problem. Testing voltages, as someone mentioned, is also a good idea. Check also for wires with frayed or melted insulation shorting out against a bolt or the chassis. Check the voltage drop across all resistors in the power stage for signs of failure.

    As Bobby and Wally have said, a newish CE cap is not all that likely to fail -- probably the tenth most likely thing on the list of things to check.
     
    BobbyZ likes this.
  16. BeegReeg

    BeegReeg TDPRI Member

    23
    Jun 29, 2017
    Hawaii
    Thanks. Here’s where I’m at. Since installing the new cap can the amp is dead quiet. Before - thumping on the can produced microphonics, but not now. Also, before, wiggling or tapping preamp tubes produced noise, but not now. The cap can got pretty warm during 3 hour long sets last night, but not too hot to hold. When I was having problems before I changed it out the noise was a fizzing that oscillated in pitch and was independent of having the guitar plugged in or any of the pots on the amp. I would be comfortable checking voltages - keep one hand behind your back!
     
    flyswatter likes this.
  17. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Okay...I reread the thread after your last post, beegreeg. Now, if I understand things correctly......you have recently replaced the cap can for a third time and the amp is working properly. Youre simply concerned that it too will fail prematurely. However, the symptoms when tapping the can are not now present, correct? And...the amp is working properly...as far as youhave ascertained...correct?
    If this is the situation, then imho a voltage chart needs to be worked up and biasing numbers need to be known. If all of that seems to be correct, then you have a baseline.
     
    Last edited: Dec 8, 2018
    RLee77 likes this.
  18. Faceman

    Faceman TDPRI Member

    61
    Aug 15, 2018
    Ohio
    Just a suggestion, I like to bring power supply caps up slow on a variac over around a 1 to 2 hour period. I've had brand new ones go bad prematurely as a result of, what I believe to be, going full on high voltage right out of the gate. Could be in my mind but I have never had that problem again after doing it that way.
     
  19. Silverface

    Silverface Poster Extraordinaire Ad Free Member

    Age:
    66
    Mar 2, 2003
    Lawndale CA
    Modern electrolytic caps don't need that. No manufacturers use that procedure either. A new cap does not need to be "formed" in that manner, and NOS caps (that some use by forming them over a specific time period.should not be used.

    That procedure seemed to become more known after Gerald Weber published his first book, but no professional techs I know do it - I've been servicing amps since the 70's, never brought caps up to voltage like that (and never hd a failure) and that procedure has never been commonly used as far as 'm aware.
     
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