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Lots of hiss from 70s bassman head

Discussion in 'Amps and Cabs [BG]' started by TheGeneral, Sep 5, 2002.


  1. Hey tube amp oficionados,
    I have this old 70s Fender Bassman 100w tube amp that I recently got on ebay. The seller had all the caps cleaned and the amp serviced, but there is considerable hiss from this amp, except when switched to standby. Is this typical of bassman amps or is there something I can do to quiet the thing down a bit?
    Thanks
     
  2. Paul A

    Paul A

    Dec 13, 1999
    Hertfordshire U.K!
    ????
    Caps Cleaned??????
    They NEED to be replaced!
    :eek:
     
  3. Could be a noisy tube. Try swapping in different 12AX7A's and 12AT7A. If that doesn't do it, then the plate resistors may be noisy. If you don't know what I'm talking about, take it to a tech and let him find the problem and fix it.

    It's not supposed to sound like that.

    Chris
     
  4. Thanks, guys for the input.
    I'm not sure if the caps were replaced or cleaned--I'll have to check the repair ticket. I think I'll look for a tube amp tech to check it out.
     
  5. The caps probably need to be replaced. They can't be cleaned, so if that's what the guy you bought it from told you, it was BS. The capacitors dry out after about 10 years or so and must be replaced. That's the main drawback about buying a vintage tube amp. They actually dry out even faster when the amp sits for years.
     
  6. I am going out on a limb here and say that the pots are what was cleaned, not the caps. What has been stated above should be your plan of action. These are very common amps and you should have no problem finding a tech that can whip it back into shape. Although components such as caps, resistors, etc. don't have a expiration date as alluded to above, they do have a MTBF based on time, temp, operating conditions (humid, dry), and all that other stuff. The functionality of every component is fairly easy to check by an experienced tech.

    Good luck!
     
  7. I just recapped the guitarist 67 Fender Pro reverb. It took all but the power supply caps to get rid of the hiss and egg frying sound. PS all the original tubes were good. It is a common problem if an amp has sat. They often go for years like that becase the still work. New caps will bring the amp back to life. The Pro reverb only cost 26$ in parts with a new power cord. good luck and let us know how it comes out.
    Benton