Broken off filter cap (bassman ab165)

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Lobotomie, Apr 22, 2016.

  1. Lobotomie

    Lobotomie Member

    Messages:
    848
    Joined:
    Mar 21, 2016
    Location:
    Montreal, Canada
    So this happened at band practice...

    [​IMG]

    It's one of the big 70uF filter caps in series on an AB165 Bassman (blackface).
    I'm thinking this was caused by vibrations, but I'm still pretty surprised about it.
    The replacement part is on its way... in the meantime, I'm curious if removing that cap from the circuit while the amp was on would have damaged any other part of the circuit, or tubes for that matter.
    Would anybody care to speculate on this?

    Anyone run into this kind of problem before? I'm thinking about putting a strip of hot glue at the base of these caps to hold them in place and dampen vibrations.

    Thanks for the input!
     
    Last edited: Apr 22, 2016
  2. PushedGlass

    PushedGlass Member

    Messages:
    413
    Joined:
    Sep 26, 2014
    It would be very reasonable to hot-glue or silicone-glue down those caps so that they're supported by their bodies in addition to their leads. This open-circuit condition would have made the amp go bonkers with hum but I don't think it would have hurt anything.
     
  3. Lobotomie

    Lobotomie Member

    Messages:
    848
    Joined:
    Mar 21, 2016
    Location:
    Montreal, Canada
    It was more of a "bacon in frying pan" sound and a big loss of output.

    Fortunately my buddy's V4 was sitting nearby, so I got to try it out.
    Wow these things can sing!
     
  4. xtian

    xtian Member

    Messages:
    1,796
    Joined:
    Dec 15, 2010
    Location:
    NorCal
    Fender put a foam strip inside the doghouse to help hold those caps steady.
     
  5. Lobotomie

    Lobotomie Member

    Messages:
    848
    Joined:
    Mar 21, 2016
    Location:
    Montreal, Canada
    Aha! That's interesting. I bought this amp with a missing doghouse, it might be a good idea to replace it then. Thanks for the info!
     
  6. KissTone

    KissTone Supporting Member

    Messages:
    2,592
    Joined:
    Dec 29, 2002
    Location:
    Pgh., PA
    The only problem there is that most new production filter caps (like F&T, Xicon, Illinois. etc.) are physically much smaller than their 'vintage' counterparts, so the foam under the doghouse isn't thick enough to provide any downward pressure on them.
     
  7. Lobotomie

    Lobotomie Member

    Messages:
    848
    Joined:
    Mar 21, 2016
    Location:
    Montreal, Canada
    Good point. I have a big piece of foam I cut bits off of to put under pickups in guitars I service; I'll just stuff more of that in there.
     
  8. KissTone

    KissTone Supporting Member

    Messages:
    2,592
    Joined:
    Dec 29, 2002
    Location:
    Pgh., PA
    Before you do that, hopefully one of our more knowledgeable members will chime in and confirm that just 'any old foam' is safe for this application. I know that Fender usually used a pretty dense, closed-cell foam---so I don't know if the foam needs to have any certain qualities.
     
    Last edited: Apr 23, 2016
  9. swiveltung

    swiveltung Member

    Messages:
    14,549
    Joined:
    Feb 5, 2011
    Location:
    PNW
    Just adjust the foam you put in to the thickness you need. But frankly, I think you must have had a bad solder joint or something (cant open your picture) A lot of amps have filters that aren't under doghouses and don't break a filter. It probably got damaged.... not from the vibration.
     
  10. Baxtercat

    Baxtercat Member

    Messages:
    11,079
    Joined:
    May 11, 2009
    Location:
    just west of Monterey, CA
    Can't see the pic here either.
    Replacement cap covers are available [if this hasn't been mentioned yet].
     
  11. Lobotomie

    Lobotomie Member

    Messages:
    848
    Joined:
    Mar 21, 2016
    Location:
    Montreal, Canada
    The lead from the cap actually broke off, the solder joint is fine.
    It seems like you can't link images from google images on forums anymore... I'll try it again.

    [​IMG]

    Anyway, I'll just replace the cap, order a replacement doghouse and stuff it with foam.
    Thanks for the input guys.
     
  12. zenas

    zenas Member

    Messages:
    6,672
    Joined:
    Jul 1, 2011
    Go to the hardware store and buy a roll of weather stripping. It's got adhesive on one side just like the stuff Fender used.
    Cost under 10 bucks and one roll does alot of Fenders.

    Off the top of my head I don't remember the dimensions but it ain't too hard to figure out.

    And never use an amp without a dog house.
     
    Jeff Gehring likes this.
  13. pdf64

    pdf64 Member

    Messages:
    5,497
    Joined:
    Aug 9, 2008
    Location:
    Staffordshire, UK.
    Yes, it presents a horrible electrocution hazard.
     
    guiltless and Jeff Gehring like this.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice