1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  

Peavey Tube head...Four preamp tubes...what do they do?

Discussion in 'Amps and Cabs [BG]' started by SherpaKahn, Nov 16, 2006.


  1. SherpaKahn

    SherpaKahn

    Dec 1, 2005
    Bronx, NYC
    Okay, so I just picked up a Peavey VTM 120 tube amp head last week, and I'm quite happy with it, even though it is a guitar head. It has a very aggressive sound, but as it is EQ'd for guitar, it can be a bit too trebly and harsh. I like a bite in my sound, but it's a bit much. What really annoys me is that the high-gain channel is virtually unusable for me once the gain goes past '3'; it's just too fuzzy and distorted. I understand that "high-gain" for guitarists means something very different for guitarists, so I'd like to tame the gain stage a bit. I figure I'll use an external EQ pedal to boost the low-mids and lows, but I still have the distortion problem, so I've been wanting to switch out some of the 12ax7 tubes with lower-gain preamp tubes, but I am uncertain what the role each tube has, and which would be best to replace to get a warmer sound. Any advice would be appreciated. Thanks!

    -Stephen
     
  2. SherpaKahn

    SherpaKahn

    Dec 1, 2005
    Bronx, NYC
    Do the bump. I think the last tube on the right is the driver tube, but I'm not sure.
     
  3. my Classic 400 has 5 preamp tubes.

    the last is a 12AT7 and is the tube driver... I'd find a schematic for that specific model if you want to know for sure.
     
  4. I think you can reduce the gain of an amp by switching some of the grounding capacitors on the premap tubes. Take it to a tech they should be able to tell you if it would work, and it would be a relatively cheap fix.
     
  5. BbbyBld

    BbbyBld

    Oct 13, 2005
    Meridian, MS
    I tried to find a schematic at the office yesterday...it seems to be missing from the file!

    In the meantime, have you tried changing the dip switch settings? One of them (comp) adds in diode clipping, which may be responsible for the fuzzy distortion you talked about.

    The tube closest to the output tubes will be the splitter
     
  6. A9X

    A9X

    Dec 27, 2003
    Australia
  7. ldervish

    ldervish

    May 22, 2005
    Johnson City, TN
  8. BbbyBld

    BbbyBld

    Oct 13, 2005
    Meridian, MS
    Thanks...that's helpful, but sad in a way that I have to rely on the net!

    Anyway, looking at that, it's pretty obvious which tube does what.

    I don't think replacing tubes will help much. It would be better to modify the amp. That amp has the "James Brown sound" as we like to call it (he was a guy who designed a lot of Peavey amps). That really doesn't lend itself well to good bass tone.
     
  9. SherpaKahn

    SherpaKahn

    Dec 1, 2005
    Bronx, NYC
    Wow, thanks for all the responses!

    I'm curious why switching the tubes wouldn't do much; is it a matter of the EQ not being conducive to good bass tone? I intend to put an EQ pedal in the effects loop to help out a bit, but I'd really like to be able to use the high-gain channel and get a let fuzzy sound.

    As for modifying the amp, what would that entail? Would it simply mean switching out select capacitors and replacing them with higher-value caps? I think I'll take it in to a tech, but I'm just curious, and TB seem the place to ask these questions.

    Thanks!

    -Stephen
     
  10. SherpaKahn

    SherpaKahn

    Dec 1, 2005
    Bronx, NYC
    Well, switching out three of the preamp tubes with EH 12ax7s helped out the harshness problem immensely. The gain is still too high for bass on the high-gain channel, but at least it's not harsh and screechy anymore. I'm looking to pick up some 12au7s and play around with them to see how many I need to get to a good level of gain. I guess the old preamp tubes in it (Sovteks, I think), were just way way too harsh. Someday when I can afford it, maybe I'll replace the power tubes with something smoother.
     
  11. Willem

    Willem

    Dec 26, 2005
    Belgium
    12at7's or 12ay7's would help to reduce gain. 12au7's gonna cost you a lot of volume.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.