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SVT-2 PRO problems

Discussion in 'Amps and Cabs [BG]' started by NKBassman, Mar 9, 2011.

  1. NKBassman

    NKBassman Lvl 10 Nerd Supporting Member

    Jun 16, 2009
    Winnipeg, MB, Canada
    Ok, sorry this is a long post, so please stay with me.

    I bought a used SVT-2 PRO a few months ago. At lower volumes things seem to work fine and the tone sounds great, but I’ve never really felt the amp had the skull imploding power so many people claim it’s supposed to have, and nowhere near the shear awesomeness I had achieved with a borrowed SVT-CL for a couple of practices. I routinely find myself with the master volume between 2 and 3 o’clock just to keep up with the guitars through either an Emperor 2x15 or a pair of ghetto 4x10s.

    Around Christmas it was showing a problem with one half of the output bias LEDs that was progressively getting worse. I took it to a tech, and he said there was a problem and replaced the output tubes with a brand new matched sextet of JJ 6550s. He also replaced all the 12AU7s, but said the 12AX7s were fine. He biased the amp and I felt the overall tone was generally improved.

    I’ve played it at a few practices and a few gigs since then, but now I’m starting to notice some issues. A few weeks ago it randomly flipped into standby while having been on for an hour or more. I turned the standby switch off for a minute or two, and then back on, and it seemed to work fine again. It sounded ok, so I shrugged and carried on playing.

    Last night after warming the amp up for over 20 minutes in standby, when I flipped the switch it seemed to stay in standby a lot longer than normal before the Green power light came on (maybe 15 seconds, VS 5 seconds normally). When it finally kicked in there was a pretty bad hum even with no signal present. I checked the bias LEDs and both were green when no signal present, but while playing only one side would flash red. The other side just stayed solid green the whole time, no matter the gain or volume settings on the amp. I tried fiddling with the bias adjust on that side, and no matter how I turned it I could not get the red LED to flash while playing. Turning clockwise it stayed green until both green and red came on. I noticed that immediately after fiddling with the bias adjust the hum had disappeared, so I set the knob roughly back to where it was before I started messing with it and continued playing. However, I swear the gain knob was now reacting differently than before I messed with the bias, ie things now sounded more distorted at the same gain level as previous to my messing around.

    Things were fine for about an hour until the amp suddenly started making a quiet but very noticeable hissing-squeal type sound. I was in between takes and had been completely unplugged from the amp for a few minutes when it just randomly started. Bias lights looked fine, overall tone was unchanged when playing, but it was making noise. Then after about 5 minutes it just went away as randomly as it started.

    Think it’s a bad preamp tube? Could one of the tubes have vibrated loose? (that Emperor cab vibrates like there's no tomorrow). Think I’m just paranoid? I’d like to hear my options before taking it back to the tech for another $150 bill.

    Thanks for looking,
  2. jackcheez


    Sep 13, 2010
    Long Beach, CA
    It's not well. :rollno:

    Tech time again. :(
  3. NKBassman

    NKBassman Lvl 10 Nerd Supporting Member

    Jun 16, 2009
    Winnipeg, MB, Canada
    Thanks. :(
    I just got a hold of the tech that fixed it last time and explained the bias light issue to him, and he immediately suspected the phase inverter tube might be to blame.

    I'll bringing it in tonight and report back, in case anyone else has this problem.
  4. NKBassman

    NKBassman Lvl 10 Nerd Supporting Member

    Jun 16, 2009
    Winnipeg, MB, Canada
    FYI, my tech confirmed it was indeed the phase inverter tube. I've only been able to run it once since I got it back, but everything sounded much cleaner, and there seemed to be more headroom available on the master volume control.
  5. Alex1984


    Jan 16, 2010
    Good thing you got it fixed. Weird you'd be finding the head to be quiet, do you still have that problem now (what kind of cab are you using)? Hope your tech didn't charge you anything for that.
  6. NKBassman

    NKBassman Lvl 10 Nerd Supporting Member

    Jun 16, 2009
    Winnipeg, MB, Canada
    No he didn't charge me anything. I've only used it at one practice so far since the fix, through a pair of junky 410s, but when I noticed the problem originally I was playing through my 215. The extra speaker area of the two 410s may account for the perceived increase in volume/headroom.

    Unfortunately I'm going out of town this weekend, and then moving as soon as I get back, so I probably won't get a chance to try it with my 215 for another month still.

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