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Super Reverb-Breaking Bad?

Discussion in 'Amp Central Station' started by backalleyblues, Apr 26, 2015.

  1. backalleyblues

    backalleyblues Friend of Leo's

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    Howdy gang!

    A problem developed with my SR over the weekend-virtually every note below D (open D string) was distorting quite badly with the amp on 3-this was happening on a festival stage this weekend so needless to say, it was not a fun time...

    The skinny on the amp-'73 chassis housed in a 2x10 cabinet (JD Newell) loaded with Emi 1028k and 1058 speakers, running a 4 ohm load. Black faced properly by a tech I trust completely...

    So besides the speakers, what else should I be checking for? AFAIK, the filter caps were changed with the blackfacing but if I need to double check them, I can... Bad tube? It was a bit better when I changed to the normal channel, but not totally clean...

    I'm all ears to your ideas... I'll be at the festival again today (stage manager) so I won't be able to tear into the amp until tonight.

    Thanks in advance,
    Franc Robert
     
  2. BobbyZ

    BobbyZ Doctor of Teleocity

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    What about the cathode bypass electrolytics? Some guys leave them.
    Of course the first thing to try is tubes. Does it happen on both channels? If so that narrows it down to the phase inverter,power tubes and rectifier tube.
    Could even be a bad connection.
     
  3. homesick345

    homesick345 Poster Extraordinaire

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    Check the power tubes (are they both working?), change them to see, & change the rectifier if you got a spare

    Change the small tubes also to see if any change

    Hope you have spares |& could experiment
     
  4. backalleyblues

    backalleyblues Friend of Leo's

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    Both power tubes and rectifier were on (all were hot) so at least it wasn't a bad heater... More tonight once I check it through (and I do have a spare set of tubes)

    Franc Robert
     
  5. flyswatter

    flyswatter Friend of Leo's

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    My first thought also is power tubes. When the old ones on mine went the effect was identical to what you are describing.

    Sometimes on older amps the tube sockets get loose, causing a bad connection with much the same results, even when the tubes are fine.
     
  6. backalleyblues

    backalleyblues Friend of Leo's

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    OK, here's what I've found so far...

    1) Speakers are good... plugged them into another amp (my Carvin Vintage 16) individually and brought the volume up to normal... no buzzes at all, on either one...

    2)Tried both channels-the normal channel seems to have gotten a tweed treatment, and is decidedly dirtier and midrange-y, but the low-end distortion I'm hearing was not there. Switched over to the reverb channel, and sure enough, it was there... swapped in another tube into V2, and it's somewhat better, BUT there is also this spark-like sound I'm getting out of the amp-I thought it was my wireless doing this, but I'm plugged into the amp with a straight cord right now...

    3) As I'm typing and checking things, I turn the bass pot all the way off, and I get no bass at all (duh!) turn it back up, it went from no bass to normal in almost no time, and basso profoundo not much past that... but NO BUZZ!!! Hmm, I know it's due for it's annual cleaning (probably overdue) but I never thought a pot could cause a distortion like that...

    Put the original preamp tube back in, it's clearly the tube... I've got a spare, so no immediate issues here... but I will try rolling in a couple different ones into V2 over the next few days... I'm all ears on suggestions, new production or good NOS...

    More updates in a day or so, after I've cleaned the chassis again (contact cleaner, etc).

    Franc Robert
     
  7. BobbyZ

    BobbyZ Doctor of Teleocity

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    You might try another tube in V4. That's the reverb recovery and a gain stage for the vib channel.
    If the normal channel works ok then V2 and V4 are the ones to try.
     
  8. backalleyblues

    backalleyblues Friend of Leo's

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    Thanks Bobby, I'll do that tomorrow when I pull the chassis for cleaning.

    Franc Robert
     
  9. flyswatter

    flyswatter Friend of Leo's

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    To answer your query on tubes, a full set of JJs in your preamp would not be a bad idea. I replaced all the tubes in my SF Super Reverb with JJs two years ago, and it has been running perfectly as a gigging amp ever since.
     
  10. backalleyblues

    backalleyblues Friend of Leo's

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    Flyswatter,

    The tube that died was a JJ (as is all the other tubes in this amp). Granted, it's been in there for 5 or more years (as long as I've had this amp, in fact) and has been played on hundreds of gigs... not opposed to another JJ, but I wouldn't mind trying other flavors. Got an E-H in there now, and it sounds good too... we'll see what tomorrow brings...

    Franc Robert
     
  11. backalleyblues

    backalleyblues Friend of Leo's

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    OK, now the update...

    Pulled the chassis, sprayed all contacts, checked the filter caps (Sprague Atoms, look fairly new, they're ultramarine blue, if that means anything), went poking around inside the chassis-man this chassis has gotten bent up!!!

    Exercise all the pots after spraying, and I notice the bass pot is not behaving AT ALL, so I have a closer look at it... something must have hit the face of the amp at some point recently, and it knocked the shaft back into the pot body, knocking loose the shell... somehow (my dumb good luck!) I manage to get the shell to snap back on, with a very satisfying click. Put the amp back together, fire it up to normal volume-my buzzy bass IS GONE COMPLETELY!!! Suuhhh-wweeeetttt!!!!

    I know, I know, I'm going to order a new pot for the bass control tonight (and a good ol CTS pot at that!) but at least it's back up and running... I'm also thinking maybe I need to get a proper road case, instead of the Tuki cover I've been using...

    Thanks again for the help!

    Franc Robert
     
  12. flyswatter

    flyswatter Friend of Leo's

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    Well, that's the happy ending we were all hoping for. Congrats.
     
  13. muchxs

    muchxs Doctor of Teleocity

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    New CTS pots have a different feel than the old ones. They feel smooth 'n' sexy. They're better built even though the new ones are made somewhere offshore while the originals were U.S. made.

    The new ones have nice brass shafts. The old ones have plastic shafts.

    If the "changed pot feel" bothers you and it might 'cuz the new pot will certainly feel different... I have a few period correct originals that haven't taken direct hits in their relatively sheltered lives. :cool:
     
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