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late 70's SVT head, what power tubes?

Discussion in 'Amps and Cabs [BG]' started by Tim Cole, Sep 16, 2005.

  1. Tim Cole

    Tim Cole Supporting Member

    Jun 12, 2002
    Findlay, Ohio
    Well, I finally got my SVT, and messed with it a little yesterday and today.

    First impressions.....for all of the legend of the massive volumes, I was a little disappointed. It's loud enough for a band, but not much more. The sound also breaks up quite a bit into the svt "distortion" very quickly. If I dial the mids out, you can dime the amp and be at a pretty low volume level, but it cuts out the overdrive.

    I took the amp up to my bud cheezewiz to check out today, and I decided to take the back cover off to check things out. Well, there was the problem, I'm guessing. In the middle are 4 peavey branded 6550a tubes, and on both ends are sovtek 6550s. I suppose someone pulled their good tubes, and shoved whatever else they had in it before the sold it. The preamp tubes appear to be the original RCA's, and I see no reason to replace them.

    So needless to say, I am in the market for a new set of power tubes. The svetlana "winged c" 6550's are a likely candidate. I want something that will be close to an original SVT sound, but would also like to be able to drive it pretty hard without getting the buzzsaw distortion. I've read these winged c tubes are about as close as you can get to the originals, without paying and arm and a leg for OEM. Do the tubes need to be matched?

    Any references as to how to bias the tubes? I am somewhat handy, and would like to learn to do so myself.
  2. I hear the JJ KT88's are good, i wish i'd used them, but the tech put in Svetlana 6550's

    If you can find some Sylvenia 6550A's, they'd be nice, they were while they lasted in mine :(
  3. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    IIRC, If you pop the front grille off, there should be test points and directions on how to set the bias. You're going to need a BIG ol' load resistor though...
  4. Tim Cole

    Tim Cole Supporting Member

    Jun 12, 2002
    Findlay, Ohio
    Stupid question....how do you pop the grill off? Is it like the newer ones you just pry off with a screw driver?

    I did some research, and ordered a complete new set of tubes from fliptops.net....

    : 6pc. 6550 (SVETLANA WINGED C), 4pc. 12DW7 (JJ/TESLA), 1pc. 12AX7 (JJ/TESLA), 1pc. 6C4 (NOS), 2pc. 12BH7A Ei.

    I'd like to get the caps and resistors checked out as well, not sure about doing any of this, so I plan to take it to a local audio shop who is experienced with tube amps in general, but want to make sure things are done to SVT spec to have it running at it's top potential.
  5. Tim,
    If your looking for a backup set of NOS tubes, I have a complete set less (1) 12AX7 that I want to sell.
    Just make me an offer.
    The power tubes are NOS GE's ,they are not matched.
    Anyway.....if your interested.
  6. Tim Cole

    Tim Cole Supporting Member

    Jun 12, 2002
    Findlay, Ohio
    PM sent ;)
  7. eric atkinson

    eric atkinson "Is our children learning "Is our teachers teachin

    Feb 4, 2001
    You might do a search for a place called fly by night music. It is local strore here in Joplin.. They used to sell stuff online a couple years back but not sure if they still do. But he had tones of this stuff in stock! I will stop by tommorrow if i can and see what he has around!! Might be able to get them for alomst nothing!
  8. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    There's nothing wrong with your question...it's always good to ask. It's been 5 or 6 years or so since I owned the '73, but I believe that it just used those plastic snap in fasteners (like a grille cloth) to hold it on. I'll have to look for photos today...

    You might want to PM Psycho Bass Guy, he's far more experienced with SVTs (and tube amps in general) than I am.