Would bad tubes cause overdriven fizz

Discussion in 'Amp Tech Center' started by tapollok, Feb 26, 2014.

  1. tapollok

    tapollok Tele-Holic

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    I have a Genz Benz Black Pearl
    It's a 30 watt EL84 amp based, as I read, on the AC30.
    It has a master volume and a foot-switchable boost.

    I just recently started using it without effects...straight in.

    But I am finding the top-end of the overdriven sounds to be fizzy...a very unpleasant fizzy----almost an overtone of fizz---with all my guitars...and regardless of EQ.

    The speaker is a 12" Red Fang.

    I have an issue with a microphonic tube...metal-on-glass.
    I re-tubed the original Ruby's with JJ's last year.
    Took it to a tech for a once-over 6 months ago...he replaced the microphonic tube...but that one, or another went shortly after.

    Could a bad tube, power-preamp-rectifier, cause this fizzy overdrive?
    Clean settings are stellar.

    I don't know what speaker cone cry sounds like. Could that be it?

    Sorry if this is not specific enough.
    I don't want to waste time with another tech...want to begin learning myself.

    Thanks,
    Tom
     
  2. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

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    Short answer, yes.

    Turn the amp on and gently tap the tubes with the eraser of a pencil or a chopstick. If one of them is louder, try swapping it out for another. Or, if it's really microphonic, you'll know right away!
     
  3. Frodebro

    Frodebro Doctor of Teleocity Ad Free Member

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    Many master volume amps will sound fizzy if you have the gain cranked up but the master volume set too low.
     
  4. ProToneThinline

    ProToneThinline Tele-Holic

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    Tom, what preamp tubes are you using? Modern tubes have been known to be bad right out of the box. Also, not sure about the BP, but some amps (like the Vox AC15/30) generate a lot of heat, so tubes cook rather quickly.

    I wouldn't expect cone cry, since you're only getting the fizz on overdriven sounds....

    I have a few old US-made 12AX7's left in my stash. You're welcome to come over some time and try them out (yes, I'm back home now). PM me if you're interested.

    K
     
  5. Cirrus

    Cirrus TDPRI Member

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    Man, I miss my Black Pearl. It's one of the few things I regret selling.

    Yeah, as already mentioned it could well be a tube. In particular, I can't remember but I thinkthe black pearl has a cathode follower setup in the preamp, so one of those 12ax7s will be run harder than the others.

    Fizz could also be a blown speaker (sometimes they blow and sound fine except for a bit of fizz!) or a bias issue in any of the tubes, or a bad cathode bypass cap, or a dodgy resistor... there's a LOT that it COULD be, even if the most common culprit is a tube.

    I got mine along with perhaps 6 other people as a store here in the UK was blowing them out cheaply, I think of the 6 mine was the only one that didn't have problems with crackles/ blowing valves etc - the rest all had to return for different problems. So it might be something like a cold solder joint etc. Really, your only option is to replace valves and if that doesn't help go get the multimeter and soldering iron out/ get a tech involved!

    And yes, they do run "AC30 hot" - that's why they put a fan in it!
     
  6. tapollok

    tapollok Tele-Holic

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    Thanks Axis.....the tube that is known to be microphonic rings out glassy and fades out as a note fades. I had a preamp tube changed last Aug when I had a routine checkup....the tech had to go thru several to get one that didn't ring...I'll be checking them all soon.


    Frodebro: Thanks...I have been told that this amp was designed to run with the master at below 1:30....others have said they love the sound of the gain dimed with master at any level...not workin for me yet.

    Current issue aside, this amp sound crazy-good at conversation volume...I was gonna buy a 5f1 clone but realized I already have that in spades if I want it.
     
  7. tapollok

    tapollok Tele-Holic

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    Sure, you just wanna give 'er a go....I know you've got GAS at the moment! :D

    Thanks for checking in! Heard you were in town. Would be great to get together.

    It's loaded with JJ's all around except for the original Ruby 5AR4. I put a matched quad of EL84's in when I got it...but that was 18 months ago...and has to be well over 600 hours on 'em...so...
    I play it every day 1 hour min.
    It has bomb-proof retainers on all tubes and it's a pain to take them off...
    I was gonna just order a full set...all 10 tubes....love to pick your brain.
    Will PM you later.

    Thanks again for dropping in.
     
  8. tapollok

    tapollok Tele-Holic

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    Thanks,

    I feel fortunate that while I still want a few more amps...I won't have to give up the Pearl.

    I always run the fan...silent as falling dust.

    Thanks.
     
  9. tapollok

    tapollok Tele-Holic

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    The Black Pearl tube layout
     

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