Swap 12ay7 for 12ax7???

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by slegros, Mar 25, 2008.

  1. slegros

    slegros Member

    Messages:
    499
    Joined:
    Sep 9, 2007
    Running either my Strat or LP into my 18w Ampeg Jet reissue I love the natural crunch I get from the amp, but find I have 2 problems. Not enough separation between clean and O/D when using an O/D pedal at decent clean volume, and feedback from the LP at fairly low volumes despite using the lo input.

    I'm thinking of swapping a 12ay7 for the 12ax7 in V1 to reduce the gain in the amp to basically get a cleaner amp, and get my crunch from the pedals. Anyone else try this? Any suggestions? Anyone else running a 12ay7 in V1 on a twin EL84 amp? Thanks in advance!
     
  2. Blue Strat

    Blue Strat Member

    Messages:
    30,036
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    It may help somewhat though you'll have to increase the volume control to get the same volume which might land you back where your started. If the distortion is occuring in the preamp of the amp it's more likely to help than if it's occuring in the power amp.
     
  3. slegros

    slegros Member

    Messages:
    499
    Joined:
    Sep 9, 2007
    Thats my sneaking feeling, that I'm getting the distortion in the preamp section before I can really drive the power tubes. Am I right in thinking that the 12ay7 will let me drive the power tubes harder for the same volume?
     
  4. Axemeister

    Axemeister Member

    Messages:
    2,135
    Joined:
    Jan 27, 2003
    Location:
    La La Land, CA.
    I am not an expert, but I think if you are dealing with preamp gain/distortion you can also try a 12at7 or 5751 for different preamp results.
     
  5. Blue Strat

    Blue Strat Member

    Messages:
    30,036
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    No, that's an internet myth. The only way to get the power tubes to break up is to play loud. Using a lower gain preamp tube makes the power tubes run cleaner.
     
  6. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

    Messages:
    8,822
    Joined:
    Oct 14, 2005
    Location:
    Berkeley, CA
    Just a clarification here - if an amp has a master volume, you can turn that up to get power-section distortion, but not necessarily have to be louder. Replacing the V1 preamp tube with a lower gain sub may allow you to then raise the master volume level and achieve the same volume.

    - Thom
     
  7. JimiStiff

    JimiStiff Member

    Messages:
    381
    Joined:
    Nov 24, 2006
    Location:
    Altach, Austria
    i just did that yesterday on my fender bassbreaker...and i'm lovin it! Give it a try..this tubes are cheap...
     
  8. Blue Strat

    Blue Strat Member

    Messages:
    30,036
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    How can you turn the master volume up without the amp being louder? The master volume is just another volume control that feeds signal to the power tubes. Turn it up and the volume goes up and if you're loud enough, the power tubes break up.

    The only way to get the power tubes to break up is to play loud (enough) or set the amp to high levels with an attenuator.
     
  9. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

    Messages:
    8,822
    Joined:
    Oct 14, 2005
    Location:
    Berkeley, CA
    Drop the preamp gain with a lower-mu tube, the volume goes down. Raise the master volume up to the same overall volume as before, and, voila!... you've shifted the source of overdrive toward the power section. Being at the same overall volume, you won't get any additional speaker breakup. I've done this a bunch of times - seems pretty basic to me.

    - T
     
  10. Blue Strat

    Blue Strat Member

    Messages:
    30,036
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    ...ONLY if the preamp was distorting before the power amp before the preamp tube swap. Otherwise, you're exactly back to where you started.
    In most amps both the preamp and power amp start breaking up at the same time unless it's a master volume amp with the master turned down.

    And to the original point (as I understood it) the power tubes will only break up if they "see" enough signal from the preamp to be driven hard (played loud).

    Generally, this question is asked because the poster wants power tube distorion at lower volumes.
     
  11. Blue Strat

    Blue Strat Member

    Messages:
    30,036
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    In a word, "no". Using a 12AY7 is like turnnig down the preamp volume. Turning down the preamp volume drives the power tubes less hard and allows them to run cleaner.
     
  12. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

    Messages:
    8,822
    Joined:
    Oct 14, 2005
    Location:
    Berkeley, CA
    Agreed - and this is most often the case, especially with modern amps.

    - T
     

Share This Page