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Ampeg SVT II => DIY Tube replacing?

Discussion in 'Amps and Cabs [BG]' started by Krohurte, Dec 16, 2012.

  1. Krohurte


    Jan 19, 2011
    I need to replace all my tubes in my Ampeg SVT 2 (NOT the pro model). It's been done before in a shop but isn't it doable by myself? Out of sockets, in to sockets and done? I've exchanged the little fan that's in there before but that's about it with my amp doctor proficiencies.

    Now if possible without too much hassling and knowledge, which brand of tubes do you recommend?

    Most probably it's these types:

    Pre Amp (4 x 12AX7, 1 x 12AU7)
    Power Amp: Tubes (6 x 6550)

    (this according to the SVT 2 pro specs, but I guess my not-pro uses the same tubes...)
  2. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    Yes but if I am not mistaken the II non pro has no auto bias built in so you will need to bias your new tube set if you don't know how to do this
    You would be advised to let a tech do it.:bassist:
  3. bassguppy

    bassguppy Supporting Member

    Jan 8, 2003
    Las Vegas, Nevada
    why replace all the tubes? Send it to a tech.
  4. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    No bigger waste of money on earth than completely retubing a tube amp when it's likely only one or two tubes at the most are bad.
  5. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    +10...... And maybe NO tubes are bad...... The amps have been out long enough to maybe require one change in some units..... but TWO changes?

    Tubes simply don't automatically get "worn out" that fast, no matter what it says in the silly manuals..... I never agreed with that guff, but it got printed anyhow.

    It's POSSIBLE to need them , but not a guarantee....

    WHY do you think your 20 yo amp needs it's third (at least) *complete* set of tubes?
  6. Krohurte


    Jan 19, 2011
    oh yes i forgot about the bias setting. I can't do that i guess.

    There might only be one bad tube (there is a farting noise), but since I haven't changed any of them in about ten years, it's about time for all of them anyway, no? I don't have sound loss issues, though. Only that farting, overclipping noise when I hit the E string up to 4th fret.
  7. Krohurte


    Jan 19, 2011
    because somebody told me and the internets says it too. :)

    and as said, there's that clip noise, but no other issues. so where am I now?
  8. You may have one microphonic tube from your description (or dirty jacks, pots, loose or dirty tube socket pins, bad ground). You can throw all that cash at it and wind up with the same or worse troubles from brand NEW microphonic tubes. Note Jerrold was an engineer at SLM/Ampeg so take his advice. Myself over 40 years in amp repair and 20 years spent in design. See a good tech unless you like spending money WAGing (Wild $$$ Guess). :)
  9. Krohurte


    Jan 19, 2011
    obvious good advice is taken. thanks. :)

    but here's a question then:

    a regular changing of tubes is NOT necessary? a myth rather? better wait till there's real issues like sound quality drop and the such?
    usually i am the non-hysterical type and do wait for real problems before panicking, but i thought oh well, after 10 years a-rocking it really might be about time.
  10. Yes tubes are a electro-mechanical device (valve) but no "moving parts" to have mechanical "wear". Would you replace a wife/husband after ten years just because they have been around for that long? Add to that the tubes you purchased 10 years ago just maybe better quality than those you can purchase today (leveling the difference). A rebias maybe in order to account for drift. If you notice strange operation (drop-outs, hum) then testing may revel the need for replacement.

    Replacing "just because" only causes wear to tube sockets and wallets.
  11. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    OP please note that Jerrold is an EX Ampeg engineer and B-string is an acknowledged tech.

  12. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Tubes should be changed only when they're broken, and you should try to isolate it to the broken one and replace only it, unless it's a power tube that broke, and then you should only have to replace 3 at the most to keep them matching on each side. Having said that, I've popped in a single power tube on my SVT in an emergency and it worked just fine, but it can cause the other tubes to wear prematurely.

    (NOTE: The above is only for SVT's and their power tubes. Other amps have different methods of wiring power tubes, but SVT's have them wired in triplet sets that bias separately.)

    Yes, there are a lot of myths surrounding tubes, and almost all of them are because of a single book written by the former head of Groove Tubes, who was looking to sell more tubes.
    born2lift likes this.
  13. BogeyBass


    Sep 14, 2010
    krackle crackle sputter putter hiss

    yah sounds like a bad preamp tube(s)

    new tubes , clean sockets, touch up with solder

    and it really is a pain in the ### to find good pre tubes.
    many of them are mirco phonic out of the box.

    can buy up to 2 to 3 tubes to find one good one
    at least with groove boobs (groovetubes) and pooptec (sovtec) tubes.

    I tried some gold pin fancy pants one at it was good out of the box
    but that might have been luck.

    but yah once they crackle and spit it needs to be done.
  14. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    What do you touch up with solder when you change tubes? And where are you finding all these microphonic tubes? Sounds like you need to change suppliers!
  15. Just so you know "crackle, spit and hiss" can also be caused by resistors and caps. New tube there might not help or help for long. :)
  16. BogeyBass


    Sep 14, 2010
    for sure absolutely

    guess i kinda loosely mentioned it. its just a good time to check sockets and solder connections.

    a crackle is usually just the plate vibrating, so easy fix new tube

    hiss or sputter is bad solder connections or resistor going out.

    once in awhile you get lucky and hiss sputter goes away with a new tube
    because the internal wire connections are going bad in the tube.

    but the common one is you hit a certain note on the bass then.. crakle
    just the plate vibrating old tube got shaked around for too long.
    larger plate tubes like 12au7 will start to take the wires with them
    so there can be a crakle then a hiss but its the internal wires shaking
    with the plate
  17. BogeyBass


    Sep 14, 2010
    Jimmy most of my bias opinion comes from changing tubes in high gain guitar heads like meas boogies soldano and some newer marshalls.

    so possible in a bass preamp a poopy tube is not so obvious

    in a high gain head with 5 or more tubes, it can be a rather pain in the butt to find good tubes.

    the 2 main problems is 1) im a perfectionist and can hear the difference , specially in boogie rectifier heads they expose every bad tube ever made 2) most of the time im using cheap tubes that were provided by the user. So maybe 3 out of the 5 they bought might be good sometimes none. then i have to hear them scream and whine that i had to buy more tubes. when they already provided the 5 or 6 they thought they needed.

    again most of the problems come from off the shelf tubes sold mainly at GC or other music stores. maybe its from shipping maybe because they sat there for a million years..i dont know?
    i dont make this krap up. but if some dude shows up with a handfull of groove tubes from the music store. I already know its gonna be a long day.

    and the garbage pc board mounted sockets is what you touch up with solder, even if they look good they are not.
    they get stressed from heat and people changing tubes. then with some newer fender heads you have to touch up the whole board
    because the power supply resistors heat up the boards and screw up the pre amp tubes and the channel switching. the extra heat will almost de solder everything so the amp will moan and sputter like crazy. its not bad resistors it just bad connections from poopy cracky lead free solder and poopy thin boards that get heated up to much.
  18. JGR

    JGR The "G" is for Gustav Supporting Member Commercial User

    Jun 29, 2006
    President, CEO, CFO, CIO, Chief Engineer, Technician, Janitor - Reiner Amplification
    A lot of the instability in high gain amps like the Recto is due to the design and physical layout, not the tubes.
  19. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Well I fear we're needlessly complicating the OP's life here with too much stuff he doesn't really need to worry about. The SVT 2 isn't a high gain amp. Doesn't even have a gain ;)
  20. Jimmy if it didn't have gain it would not drive speakers ;). I guess you meant a "gain control"? :)