ampeg svt capacitor question

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

  1. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
     
  2. matskull

    matskull

    Jun 5, 2006
    montreal
    Hey Jerrold, what do you think about the fliptops cap kit?
    I ordered one but didn't replaced the originals yet.
     
  3. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    i'm not Jerrold but Bruce at fliptops has some new caps-70/40/40uf that would be the exact filter caps for an SVT. his is currently updating his kits to use them, so the Fliptops kits will work perfectly in an old SVT. he also offers a 25uf @ 800V cap to replace the 30uf/600V cap which will also work well.
     
  4. BassmanPaul

    BassmanPaul Inactive

    Antique Electronics (www.tubesandmore.com) has the multicaps you need.

    Bassmec when redoing the power caps on an amp with a tube rectifier you have to remeber that the tube is limited in the capacitance it can drive. The GZ34/5AR4 can only use 30µF in a capacitor input supply. More than that and you can get flashover and destroy the tube.

    Paul
     
  5. look up high-pass, low-pass, band-pass, and band-reject filters.

    he's talking about making the filters more capacitive lowering the cutoff frequencies (half power point).

    its all RLC circuits. read up on it
     
  6. BassmanPaul

    BassmanPaul Inactive

    Sorry Jimmy but your post makes no sense to me. Kindly explain where you are trying to go.

    Paul
     
  7. I say go for the bigger capacitors.

    There will be a bigger instantaneous surge when you turn the amp on
    but, unless the rectifiers are operating on their very edge now (not
    likely), it shouldn't be a problem.

    The average current through the rectifiers does not change. The amp
    is still drawing the same amount of power through the circuit. The
    rectifiers will dissipate the same amount of power that they did before.

    Generally speaking, when engineers choose electrolytic capacitors (the
    big ones) for a power supply design, it is not uncommon to choose the
    smallest value you can get away with. It saves space and cost. The
    technology has improved. Capacitors are smaller today and, if you're
    going through the trouble of replacing them, you probably don't care
    about the nominal extra cost of the bigger ones.
     
  8. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    i always stay as close to the original amp's values as possible. as Jerrold said, what works in theory (higher values) can "stiffen" the amp's sound. i have seen this too many times when repairing old Fender amps that have been serviced by 'techs' that don't understand what they are supposed to sound like (putting in larger values). alot of 'electronics' guys seem to think that its okay to raise the values, but most good tube amp techs see it as a no-no.
     
  9. matskull

    matskull

    Jun 5, 2006
    montreal
    I just received the cap kit from fliptops.

    I opened my amp to look inside of it, I'm not a tech but a friend of mine is and he already supervised me once to recap an old marshall, he's confident enough that I can do it by myself, I know how to work in a tube amp so no worry, I won't kill myself, I already emptied (uncharged) the caps.

    Here's what was inside my amp (I think one or more as been replaced):
    Blue: 90MDF 200VDC
    1st Yellow: 30-600DC
    Brown: 100MDF 450VDC
    2nd yellow: 100uF 450VDC
    1st underside can (we dont see those on the pic): can't read it...
    2nd underside can: 10/10MDF 450/450VDC


    And here's what was in the fliptops kit:
    100uF 350V
    25uF 800V
    100uF 450V
    47uF 450V
    100/100M 500/500V
    50/50M 500/500V


    I've written them in the order I think they should go, example, 100uF 350V would replace Blue: 90MDF 200VDC.

    What do you think, I'm a little bit worried about the 25uF instead of 30uF on the 1st yellow....
    Let me know what you think.
     
  10. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    the 25uf cap instead of the 30 uf works perfectly.
     
  11. matskull

    matskull

    Jun 5, 2006
    montreal
    That's what my tech told me, just wanted to confirm.
    Thanks

    Otherwise, what do you think about those replacement?
    I guess I'll hear it myself but I'm eager to know ;)
     
  12. Hoss

    Hoss

    Jan 9, 2006
    Vienna, Austria
    You will love it! :)
    At least I love mine after this recap.
    Better focused bass, stronger mids and NO HUM. :cool:
    Bruce serviced hundreds of SVTs and he KNOWS whats the best subtstitute for the old cans.
    Higher capacitance would just spoil the trademark-sound of an svt.

    Look forward to it and WATCH THE POLARITY when soldering them into the circuit.
     
  13. MichaelJordan

    MichaelJordan

    Dec 31, 2008
    West Texas
    The only think I know, is that if you take apart a disposable camera, and then you charge up the camera's flash, it charges the capacitor. Since the case is off, you can take a screwdriver or knife and lay it on the camera's connectors next to the flash and it goes :eek: BOOOOOM! :eek: and sparks fly everywhere and is a good scare. It melted 2 small holes in my pocket knife. :crying:

    This is the extent of my knowledge of capacitors.

    Probably didn't help, but I thought I would share :hyper:
     
  14. Projectile

    Projectile

    Feb 5, 2009
    Although I agree with the general sentiment of this statement, it is misleading and not entirely true. CBS did upgrade some of the parts in the silverface amps when they took over the company, but more importantly they also changed Leos original circuit designs in order to increase clean headroom. The biggest tonal difference by far is a result of changes in the circuit, not just the parts. You can claim that the changes "weren't significant" because the schematic looks mostly the same, but having modded a silverface amp to blackface specs, I can say for certain that the changes to the circuit they made have a quite significant impact on tone.
     
  15. matskull

    matskull

    Jun 5, 2006
    montreal
    I'm not so sure about this one, what is the 47uF 450V suposed to replaced in the list I gave in my last message?
     
  16. B-string

    B-string Supporting Member

    Agree with you completely.
     
  17. matskull

    matskull

    Jun 5, 2006
    montreal
    It seems to me that this 100uF 450V misterious cap was added by someone else, probably to either mod the amp or to replace one side of a multicap that would have been defect.
    Does it make sence?

    Is there suposed to have 5 or 6 caps in the power section of the amp?

    thanks
     
  18. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    my '69 and '75 SVT's have five filter capacitors in the power supply, but two of them are dual caps, making a total of seven.
     
  19. matskull

    matskull

    Jun 5, 2006
    montreal
    I've got two dual cab too which are outside of the chassis, close to the transformer.

    I'm pretty sure tha 6th cap that was in there was some sort of fast repair.
    It's not the only thing to look like it was repaired in a rush...

    I'll bring the cap to my tech today and mesure them to see if one of the double one is defect or something...that might help to investigate.

    thanks
     
  20. metron

    metron

    Sep 12, 2003
    Denver
    I need to recap my SVT as well and I was wondering does the Fliptop kit the best match for values that can be found? I want to keep my amp as close to original as I can. Do the parts in the kit maintain the aesthetic of the amp? For example I wouldn't be too happy to replace one of the multicans with two caps and a pulltie. :rolleyes::D