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What Have I Got Here? SVT

Discussion in 'Amps and Cabs [BG]' started by The Ballzz, Jul 3, 2020.


  1. The Ballzz

    The Ballzz

    Nov 6, 2016
    Las Vegas
    Hi Folks,
    Got a pretty good price on a fridge with what was claimed to be a 1997 SVT Classic. Problem is identifying the head. All schematics and descriptions of the SVT Classic/SVT-CL show a combination of five 12A?7 tubes and this one appears to only have two 12AU7 and one 12AX7. What have I actually got and is it some oddball hybrid or some such?

    IMG_0493.jpeg IMG_0495.jpeg IMG_0496.jpeg

    Cabinet is chip board, OK condition, with a bit of tortured tolex and no glide rails or kick plate. one single 1/4" jack plate, labeled SVT-810E and reference to SLM Electronics.

    Head and cabinet sound amazing together and I'm a bit curious as to the power handling of the cab.

    Thanks Folks,
    Gene
     
    Yetiparty, Border and SidNitzerglobin like this.
  2. LetItGrowTone

    LetItGrowTone

    Apr 2, 2019
    The other two 12ax7s are in the preamp subchassis, in the front behind the knobs.

    Not an oddball. You need to find newer schematics.
     
    Rip Van Dan and dopejohnpaul like this.
  3. Ekajimmy

    Ekajimmy

    Nov 2, 2019
    +1
    [​IMG]
     
  4. LetItGrowTone

    LetItGrowTone

    Apr 2, 2019
    Last edited: Jul 3, 2020
  5. The Ballzz

    The Ballzz

    Nov 6, 2016
    Las Vegas
    Ahhh, I see said the blind man! :woot: Can I assume access is gained by removing the four screws in the top of the head cabinet and sliding that pre-amp module out the front?

    The amp at first exhibited a slight, low level hum, with nothing plugged in and Gain and Master all the way down. After warming up well and playing for a bit, I checked the bias LEDs and one side was red, the other green. I turned each bias pot counterclockwise to first light just the green, then both red & green off and then brought it clockwise to just light the green green. I did this to both sides and now all hum is gone. From what I can gather, this method sets the bias on the cooler side and if it gets brought from red to just turn off the red and light the green it is on the higher/hotter end of the scale? Am I understanding this correctly? If we decide to keep this amp instead of finding a V4-B, I'll dig in and give it a proper bias procedure with a meter, etc! I do have a cool bias probe that's switchable from plate voltage to bias current and know how to use it.

    Thanks,
    Gene
     
  6. LetItGrowTone

    LetItGrowTone

    Apr 2, 2019
    If you're competent to go in there, yes.

    Follow the manual, also on the Internet. It says: "For the longest tube life, but poorer tone, set each Bias to JUST AS the green LED illuminates. For shorter tube life, but better tone, set each Bias to JUST BEFORE the red LED illuminates."
    The former would be colder, the latter would be hotter.

    [There's some confusion about the meaning of the words underbiased and overbiased, as even the Ampeg guy who made the Youtube demo on how to set this used those words reversed in meaning. They should abandon those words and just say hotter and colder.]
     
  7. LetItGrowTone

    LetItGrowTone

    Apr 2, 2019
    Good idea to use the bias probe.
    After using a bias probe and doing the calculations and thinking about it, I biased mine a little into the red, so now those LEDs aren't really working for me (because they won't show me if it drifts a little). I might recalibrate the behavior of the LEDs someday.
     
    thetragichero likes this.
  8. rickdog

    rickdog Gold Supporting Member

    Mar 27, 2010
    The output stage depends on the two sides (represented by two sets of bias LEDs) being balanced to cancel hum from the power supply. The behavior you observed is exactly as expected. You can fine-tune the bias (keeping both sides in the green zone) by listening for minimum hum.

    I wish I had more need to play loud enough to make it worth moving my SVT-CL... they are great sounding amps.
     
    murphy likes this.
  9. The Ballzz

    The Ballzz

    Nov 6, 2016
    Las Vegas
    Ergo my use of "hotter" & "cooler" in my questions. Concepts can get a little dicey when negative voltage is present in the discussion. :confused: o_O Thanks for the info and links. :cool: This "fridge" is almost as neat as one that's full of beer! :D

    Many Thanks Again!
    Gene
     
  10. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    A little advice about undoing the preamp...it comes out easier than it goes back in, but taking off the back screen so you can hold it in place makes it easier.
     
    Last edited: Jul 3, 2020
    Border, HG1180 and LetItGrowTone like this.
  11. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    BTW, the serial checks out to April of 1997.
     
    HG1180 and LetItGrowTone like this.
  12. The Ballzz

    The Ballzz

    Nov 6, 2016
    Las Vegas
    Thanks for the tips! :thumbsup: And while removing the screen may seem obvious to me, can I assume it also easier with the power tubes removed? Any chance anyone could point me towards any gut shots of this or a similar amp? Always nice to have an idea of the lay of the land, prior to traveling there!

    Thanks Again Folks,
    Gene
     
  13. LetItGrowTone

    LetItGrowTone

    Apr 2, 2019
    Don't mean to intrude on the above exchange, but no, no need to remove the power tubes for easy access to the preamp.

    google images svt-cl chassis
     
  14. The Ballzz

    The Ballzz

    Nov 6, 2016
    Las Vegas
    Not intruding at all. Notice the word "anyone" in my request! :) Thanks so much for the search criteria suggestion. Gave me just what I was looking for, and then some!

    Thanks Again
    Gene
     
    LetItGrowTone likes this.
  15. DaDo625

    DaDo625 Supporting Member

    Sep 4, 2017
    Not a lot of pictures - but does this not look pristine for a 23 year old amp?
    This thing was never in the Country Bunker...
     
  16. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Nah, just hold it in a place where the power tubes aren't and you'll be fine.
     
  17. The Ballzz

    The Ballzz

    Nov 6, 2016
    Las Vegas
    Yeah, the head is in much better condition than the Titanic's anchor of an 810 speaker cabinet. Pretty close to pristine! From what I can tell, the cab is one of the ones from 7/8" chip board and is likely the heaviest fridge I've ever hefted! The rig sounds like the second coming with the Master just barely cracked open. The P-Bass with a Geezer Butler and round wounds just loves the gain at about 2:30 - 3:00, Ultra Hi & Lo off, Bass at 1:00 - 1:30, The Mid at about 1:00 and is a toss-up between #2/450 and #3/800, and the Treble at about 2:00. This leaves a SMOKIN' flat out core tone that can get anything you could ever want through simply tweakin' n twiddlin' the knobs at the bass. The dynamic response and feel is like nothing I've ever experienced before, although it sure is effing loud! If the same tones and response can be achieved, I see a V-4B in our future!
    Did I Happen To Mention, This Is LOUD?
    Gene
     
  18. Killing Floor

    Killing Floor Supporting Member

    Feb 7, 2020
    Austin, TX
    Brother, that's a sweet ride. That UPS truck under your head will take whatever you can stuff into it. Hope your neighbors are cool with it. Enjoy the heck out of it.
     
  19. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Same year? If the 5th digit is a J, it is. If not, you can figure it out by the letter:

    A: 1988
    B: 1989
    C: 1990

    Etc.
     
  20. There many more tubes in there bro. You're just focused on the back row.
     

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