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pre amp tube changing question

Discussion in 'Amps and Cabs [BG]' started by a e i o u, Jan 6, 2007.

  1. my yba 200 has been giving me alot of pick up hum so i figured i'd take the pre amp tubes out of my old fender guitar head and try it out on the traynor. i changed out the sovtek 12ax7's for the fender 12ax7s, but i don't know if i can change out the 12AU7 for the fender 12AT7. The amp has an auto biasing feature but i don't know enough about tubes to know if this is a safe change out. also, i don't know for sure but i think now i am actually getting more gain with the fender tubes which sounds good and i also believe they are distortion sooner which i like, but i don't know if thats just in my head. what i am asking is, is it safe to change out the sovtek 12au7 for the fender 12at7 (as the 'phase splitter') and, do the pre amp tubes really have alot to do with getting a different distorting sound or maybe even loosing basseyness or is it just in my head?
  2. juledude

    juledude Creator of the Monique Preamplifer and Bass Amps. Gold Supporting Member Commercial User

    Dec 10, 2006
    Santa Cruz, CA
    Owner and creator Jule Amps. Creator of the Monique Bass Preamplifier
    Two things: 1. I'd be surprised if the hum problem was caused by the tubes. It can definately happen that the tubes are the cause, but hum is most often caused by other things.

    2. No. Don't swap a 12AU7 for a 12AT7. Quite different tubes. Even with "auto-biasing." Whatever that is?

    Your question as to the pre-amp tubes effect on the overall tone is quite appropriate. That first tube has significant effect on the tone of the amp. What you describe hearing as far as "gain" is real. Quite often, different tubes, even from the same manufacturer can give different gain and tone.

    After all, it is your ear that matters.


    I'm kinda new here, and have attemped unsuccessfully to get identified as a "commercial user." I do build amps for a living, but please don't hold that against me. ;)
  3. Gothax


    Apr 22, 2006
    Heerlen, Netherlands
    Endorsing Artist: Jim Dunlop strings
    the traynor has the autobiasing feature which biases the power tubes automaticly. you don't have to bring it to a guitar tech to get it serviced.

    about the pre-amp tubes.. you can swap out every pre-amp tube for another pre-amp tube of some type without damaging the pre-amp. Just hear the difference and use the tubes you like.
  4. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    I agree with the first part, but not necessarily the second. The only difference between the 12AU7 and the 12AT7 is the amount of gain, so it depends on whether your amp will allow different gain levels for that particular tube in the circuit. http://www.thetubestore.com/gainfactor.html

    You can swap preamp tubes all day long without biasing. It's only the power tubes that need biasing. Yes, different tubes can have a dramatic effect on your sound, especially re: distortion. Do a search here on "preamp tubes" for many pages of discussion.
  5. after some playing i realize that i had alot more low end with the stock tubes, but i still am not sure about changing out the 'phase splitter' tube because that one is different than the other two. right now it has a 12au7 which acording to that website has a gain factor of 19, i want to try my fender 12at7 which has a gain factor of 60. one person said it isn't a good idea to trade this out, but others say different?

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