Pre-amp tube placement

Discussion in 'Amps and Cabs' started by scottcw, Feb 22, 2008.

  1. scottcw

    scottcw Low rent hobbyist Silver Supporting Member

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    I know the simple answer to this question is "use your ears", but I thought I would ask for experiences...

    I have a new amp with three pre-amp tubes. I think it is a bassman config - input gain, cathode follower, phase inverter. The tube chart calls for 3 12AX7 tubes.

    I have a NOS Tesla 12AX7, a GE Jan 12AX7, a GE 5 star 5751, and a GE 12AX7.

    Where would be the best spot to use the 5751 if I want to change things up? I currently have it in V1, but I am reading that people seem to use these in the PI slot. Thoughts?
     
  2. Blue Strat

    Blue Strat Member

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    I hate to be the one to say it but....."use your ears. They're the only ones that matter".

    Everyone has different objectives for doing almost anything. They also have different amps, speakers, guitars, pickups and preferences in tone, music, food.....etc.

    Have fun with it. It doesn't take much time to try every possible combination.

    I would start with V1 and try everything in that socket. Then move on to V2 and V3.
     
  3. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    I agree with Mike, only I don't really hate to be the one to say it (I don't think Mike does either). There's no substitute for doing this yourself, and Mike's recommendation on how to begin seems like sound advice (;)) to me.

    - Thom
     
  4. rockon1

    rockon1 Member

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    Again use your ears.

    Ive found of late that Ive been getting good results by "dialing in" the PI slot first contrary to the V1 like I used to do. I sometimes like a slightly lower gain tube in the PI too but given your limited selection I think the one that sounds best,regardless of gain, is of coarse the one to go with.After that I concentrate on the V1. Bob
     
  5. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    That's pretty much how it goes. I a-b test, find my preference, then move on to a-b it with the next option. I usually follow up by re-trying a reject (often times its a Telefunken), just to be sure I'm being honest with myself in rejecting it (yep, still can't find the place for those).

    After lots of experience, you get to know the sonic character of your tubes, as a kind of palette. Some people may have an easier time remembering sonic experiences than others. I find that there is also a feel factor that my body responds to, as well.

    I do not recommend doing this after smoking pot - short term memory loss complicates the process, along with the tendency to find that every tube is "the best one yet."

    - Thom
     
  6. rockon1

    rockon1 Member

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    Yep . Hoever as of late I find it more beneficial to start with the PI then go to the V1. Now if youve got virtually every 12AX7 made its even harder! Bob
     
  7. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    That's a wise strategy, Bob. I saw you post it in another thread, and I think it is a very useful method that others will benefit from.

    - Thom
     
  8. Gary Brennan

    Gary Brennan Old cavorting member Gold Supporting Member

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    I actually recently asked in the Amp technical info section about whether it was necessary to power down for preamp tube swaps. Only 1 answered, said was not necessary to power down, just flip the stanby and wait 10-15 sec. But nobody in this section said this was bad advice....

    gb
     
  9. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    I don't think it is bad advice. But I always power down all the way, even though I could just put the amp on standby. I probably do that because I got into tube swapping with my Mesa Triaxis preamp, and, since it is separate from the power amp, I'd always power it off for tube swaps.

    - T
     
  10. rockon1

    rockon1 Member

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    Well not so wise. I read of an ampmaker who stated this was how he selected his pre amp tubes so I tried it myself. I noticed a fairly pronouced difference between PI tubes. Kind of makes sense to make the power section happy first then shape the incoming pre amp tone. Ive only dialed in two of my amps this way so far but it seems I gotten better results faster. Time will tell I suppose if this is a smart "tube rolling" strategy. Bob
     

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