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!  
    TalkBass.com has been uniting the low end since 1998.  Join us! :)

Phase Inverter tube for 400+

Discussion in 'Amps and Cabs [BG]' started by Rockbobmel, Mar 9, 2004.

  1. Rockbobmel

    Rockbobmel Supporting Member

    I forgot... Can anyone please tell me which pre tube is the phase inverter for my mesa 400+ ? Thanks
  2. Rockbobmel

    Rockbobmel Supporting Member

    No One? Basstriaxis, Psycho, Mark........
  3. I don't know, which pretube is closest to the power tubes?
  4. Rockbobmel

    Rockbobmel Supporting Member

    They are not laid out that way. They are all in a straight row in front of the power tubes..
  5. Tapp


    Aug 29, 2001
    USA, Mississippi
    According to the Mesa website. The 400+ uses 4-12AX7's and 12-6L6's. So I'm sure it's a 12AX7.

  6. Fealach

    Fealach Guest

    Apr 23, 2003
    Gone to a better place
    I'd also like to know, it would be great if anyone could help out. Also, if anyone knows, how the other preamp tubes are used? That is, the 2 inputs are supposed to be "voiced" differently or somesuch. Does a certain tube belong to a certain input, so I can change that tube without it affecting the other input, or do all of them work with with both inputs, and the difference in voicing is in the circuitry? Which tube is #1 in that case? Anything would be helpful. Please forgive my ignorance if this is a stupid question, I don't know a whole lot about the inner workings of the amp.

  7. looking from the front of the amp the far left tube is the "master" tube as Mesa put it to me.
  8. Try to find some NOS 12AX7's with matched triodes and then you are covered (5751's will also work and make a good phase inverter tube.)
  9. Bob;
    On the schematic it's listed as V3 (a and b). I don't remember which one that is on the board, haven't had one apart in a while. Maybe the sockets are labelled? Sorry I'm not more helpful here...
  10. Rockbobmel

    Rockbobmel Supporting Member

    Rich from Mesa said that facing the amp front, input jacks on right, the far right tube (closest to jacks) is V-1 pre. the next one to the left is V-2 pre, the third from right is the P.I.tube. The last from right is a buffer for the power amp.
  11. Tapp


    Aug 29, 2001
    USA, Mississippi
    Sorry Bobby, Misunderstood! I thought you meant what type tube rather than where it's positioned.

  12. Yes, I'm sorry too. I thought you meant Power Input tube which is the Master Tube on the far left. I guess I didn't know what phase inverter meant, glad you called Mesa.