ampeg svt capacitor question

Discussion in 'Amps and Cabs [BG]' started by notforrobots, Jan 23, 2009.

  1. matskull

    matskull

    Jun 5, 2006
    montreal
    Ok, it's been confirmed to me that there was an added cap in there to replace one that was defect.

    So can't really just replace them the same way they were because it wasn't true to the schema.

    Does anybody here have a clear and readable ampeg SVT schema?
    The only clear one I found is from Joe Piazza but the parts numbers aren't on it...so it makes it more difficult for me to read it.

    A picture of how the filter caps of a normal svt are suposed to be hooked up would be super nice!

    thanks
     
  2. metron

    metron

    Sep 12, 2003
    Denver
    Yeah that yellow one with the white pulltie is a dead giveaway.
     
  3. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    i've got some original scans that i'll post for you.
     
  4. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
  5. matskull

    matskull

    Jun 5, 2006
    montreal
  6. matskull

    matskull

    Jun 5, 2006
    montreal
    Ok now I get it much more with this schema.

    Here's what Bruce (fliptops) told me about his cap kit:

    100uF 350V Replaces the 90/200v (bias cap) C8 on the schematic
    25uF 800V Replaces 30/600 C11
    100uF 450V - C10
    47uF 450V - IN PREAMP SECTION C23
    100/100M 500V ONE SECTION REPLACES C12A, THE OTHER REPLACES C9A
    50/50M 500/500V ONE SECTION REPLACES C9B, OTHE SECTION REPALCES C12B


    Where's that C12C?
     
  7. Kindness

    Kindness

    Oct 1, 2003
    Chicago
    Physically on that scan? In between test point C (380 V) and the output jack.

    In the circuit? Between R50 and ground.
     
  8. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    C12C is part of the 70-70-40 multicap in an early 6550A SVT (the multicaps are shown with a dotted line around them).
     
  9. matskull

    matskull

    Jun 5, 2006
    montreal
    Ok, makes sence.
    THe reason why I'm confused is because Bruce said this:

    100/100M 500V ONE SECTION REPLACES C12A, THE OTHER REPLACES C9A
    50/50M 500/500V ONE SECTION REPLACES C9B, OTHE SECTION REPALCES C12B

    So one multicap would be made with C12A and C9A and the other would be made from C12B and C9B, ignoring totally C12C.

    But on the schema is says that one is made of C12A, C12B and C12C and the other one is made from C9A and C9B....

    Why's that?
     
  10. Kindness

    Kindness

    Oct 1, 2003
    Chicago
    Because the cans they used then had values that matched those sections. Your replacements don't. You have to mix and match to get the appropriate values. Thus, you use half of one can, half of another and an independent cap to replace the three sections of C12.
     
  11. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    judging by the date codes on your picture, your SVT was made in 1978, which is identical to my '75 which uses the SVT/V9 poweramp circuit. it uses two 100-40uf caps for C12 and C9 instead of the 70-40-40 (C12) and 100-40uf (C9) as used on the earlier one.

    here's a scan i made of the SVT/V9 circuit:
    http://johnkvintageguitars.homestead.com/SVT/SVT-V9_scan.jpg
     
  12. matskull

    matskull

    Jun 5, 2006
    montreal
    Ok and that independent cap isn't supplied in the fliptops cap kit right?

    I've received another schema from ampeg that has no C12C on it...
    Did I tell you mine is a 1978?

    Here's the other schema:

    EDIT: I thought I could attach a pdf...
    Let me try to get an image instead
     
  13. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    you don't need any more caps that what Bruce supplied in the kit. examine the schematics carefully.
     
  14. matskull

    matskull

    Jun 5, 2006
    montreal
    You have been faster then me haha!

    Seriously, you just saved me so much time!!
    Thank you very much, I do apreciate it a lot.

    thanks to everyone else too
     
  15. matskull

    matskull

    Jun 5, 2006
    montreal
    Yeah I know now with the new schema, you replied while I was typing.
     
  16. anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    Here's what my tech started out with and ended up installing on my 72. ( not a Fliptop kit)

    SVTguts15.jpg

    SVTguts6.jpg
     
  17. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    no additional cap is necessary. the 70-40-40 (C12-A,B,&C) has the 70 (C12A) and one of the 40's (C12B) in parallel (=110uf). one of the sections of the dual 100uf in the kit replaces C12A and C12B.
     
  18. matskull

    matskull

    Jun 5, 2006
    montreal
    Thanks!

    Those are good caps, I recaped my vintage marshall with them.
     
  19. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    here's how i recapped my '75.

    75SVT-7-2.jpg

    i used caps from antique electronics supply (tubesandmore.com)

    i used two 80-40-30-20's (twist mount cans) to replace the two 100-40's.(the 80uf section is paralleled with the 20uf to get 100uf)
    a sprague atom 100 uf
    a sprague atom 80 uf
    and their [email protected] cap.
    don't forget that ther is another 40uf 500V (early SVT) or a 50uf/500V (later SVT/V9) filter cap up in preamp that should also be replaced.
     
  20. matskull

    matskull

    Jun 5, 2006
    montreal
    Just for my personnal knowledge, is the preamp section of my 1978 the same as the 1970's one?