Anemic Super Champ

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by PFunk, May 11, 2008.

  1. PFunk

    PFunk Member

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    Last night's gig was in a small room so I took my Super Champ. During our second set, as I started to push the amp more- master on about 6 1/2- 7, lead volume on about 5 with the gain on about 6, I started to notice a degragation with the amp's headroom. It became pretty squishy-sounding (kind of cool, actually) and wasn't cutting through the mix as had been the case earlier and at previous gigs.

    By the third set, I noticed that the pilot light was dim and when we finished out the performance the on/off switch was pretty hot when I turned it off. I had good NOS tubes in the amp- hopefully they're still good. Also, I power all of my gear with a Furrman AR 15 II regulator.

    I'm thinking that one of the transformers has issues as maybe this was the result of insufficient voltage within the amp. This happened once before some time back and I thought that it was attributed it to the wall voltage.

    "Short" of having it on the bench- can anyone offer some opinions as to whether this may be the case or any other theories?

    Thanks.
     
  2. Nolatone Ampworks

    Nolatone Ampworks Silver Supporting Member

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    Others may have other experience, but I wouldn't expect the amp to fade over time due to wall power, plus you say you have a conditioner, so...

    I'm thinking the power tranny could be getting "tired" and breaking down after good and hot, especially considering the pilot lamp going weak. The same voltage that drives the power lamp supplies the heaters on the tubes, so if you've got a shaky filament supply, that'd cause what you were seeing.
     
  3. Blue Strat

    Blue Strat Member

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    There are about 50 things that are more likely to be the problem than transformers.

    Start by testing or swapping in a known good set of 6V6s and CHECK THE BIAS...or just check the bias on the ones you have in there now. I suspect that you've lost your bias supply (likely culprit:shorted/leaky bias supply cap), the 6V6s are running wide open and overheating. Any of the power supply caps could be failing too.

    After you've done this let us know. First things first and this is definitely the first thing to do.

    If you're uncomfortable doing any of this, take the amp to a tech. It's probably overdue for a checkup.
     
  4. guitardude5

    guitardude5 Member

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    I'm not certain on what the cause of your problem is, but as a heads up to those who do know and can offer assistance, the Super Champ is a fixed bias amp.
     
  5. Blue Strat

    Blue Strat Member

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    Right. Fixed bias means that the bias must be checked/adjusted. ;)
     
  6. PFunk

    PFunk Member

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    Thanks for the replies. Would the dim pilot light be related to bias and cap issues? The problem has happened with what started out as a good pair of RCA GTA's and again the other night with my Brimars onboard. I'll have them tested as well.

    I'll have to take it in.
     
  7. Blue Strat

    Blue Strat Member

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    Take it in. It's impossible to repair amps over the internet.
     
  8. PFunk

    PFunk Member

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    Come on Mike- Think harder!
    You have the power to fix this thing Telepathically...You can do it....

    THINK!

    :)
     
  9. Blue Strat

    Blue Strat Member

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    You'd hate to see my fee for this service :D
     
  10. PFunk

    PFunk Member

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    If you can pull it off, I'll gladly pay handsomely!

    Thanks for the tips.
     
  11. Nolatone Ampworks

    Nolatone Ampworks Silver Supporting Member

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    Mike, would you expect any of this to account for a fading pilot lamp? That was the key to my suggestion.

    Cheers,

    Paul
     
  12. PFunk

    PFunk Member

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    Thats what I was wondering as well, Paul....

    Paul
     
  13. Blue Strat

    Blue Strat Member

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    Why speculate on something you can't touch or see? Put it in front of someone who knows what he's doing and let him sort it out.

    I don't understand endless threads about speculations on top of speculations on top of, often, incorrect or incomplete trouble reports.
     
  14. PFunk

    PFunk Member

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    Easy, Mike.

    I took it in, so no need to comment on speculation any further :)
     
  15. Blue Strat

    Blue Strat Member

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    Can't we speculate on what the tech will find? :D
     
  16. guitardude5

    guitardude5 Member

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    OK, maybe a dumb question... on a fixed bias amp how do you adjust the bias? I'm not tryin' to be a smart ass or anything, I'm curious.
     
  17. Blue Strat

    Blue Strat Member

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    Some fixed bias amps have bias pots, like most Fender amps, Marshall amps, etc.

    The word "fixed" confuses people. What it means is that the bias must be "set", or "fixed", as opposed to "self biasing" (AKA cathode biased).

    If there is no bias pot, you either install one or use a different value for the bias set resistor to make the particular pair of tubes you're using bias correctly.
     
  18. guitardude5

    guitardude5 Member

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    Thanks, I'm not near the amp now. If memory serves me, the only adjustment on the amp is a 'hum balance' trim pot.
     
  19. jay42

    jay42 Member

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    There isn't any bias adjust or balance adjust. The nominal setting is -33Vdc (-56V bias supply looking at a 10K to 15K to ground divider). Nominal B+ of 400V, 6V6GTA's.
     
  20. Nolatone Ampworks

    Nolatone Ampworks Silver Supporting Member

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    Because that's what the man asked for.

    It's a good thing to go in to a tech with some ideas about what the problem may be. Worth passing on to the tech, then let them do with it what they may.
     

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