Is it worth it putting a nice old tube in the PI spot?

Discussion in 'Amps and Cabs' started by CitizenCain, Jan 31, 2008.

  1. CitizenCain

    CitizenCain Member

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    I've got a couple of nice old Tungsol 12AX7s, not reissues. I've got one in V1 of my amp, V2 takes a 12AT7 and the PI is an older ('80s) Chinese/Fender 12AX7.

    Would it be worthwhile slapping that Tungsol in the PI spot or better to keep it as a spare for V1?
     
  2. scott1568

    scott1568 Member

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    From what I have heard, the PI spot is not the main tone factor. A decent working tube will suffice. V1 on most amps (Fenders anyway) is the critical spot. I would put it away.

    For example, I have 2 unidentified 12AX7's that came with my amp. Each one sounds better in V1 to my ear as compared to the new Tung Sol in there. So, I use the Tung Sol now, and put the old ones away for when I might play out or something.
     
  3. doublee

    doublee Member

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    Pardon but V1 is critical only to normal channel, no? Therefore V2 is most critical for the Vibrato (good) channel?
     
  4. CitizenCain

    CitizenCain Member

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    That's what I've heard too, that the PI doesn't really contribute to the overall tone. Just wanted to check in at the think tank and see if I'm blowing smoke up my own skirt :D
     
  5. guitarded_1

    guitarded_1 Supporting Member

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    Don't ever underestimate the ability for a PI tube to make a very noticeable difference. My secret weapon is a Mullard 4024 in the PI position on Marshall-type amps. It lowers the gain a bit, but it really makes the tone a lot more smooth and sweet.
     
  6. doublee

    doublee Member

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    We seem to have 'V1" and "P1"?
     
  7. guitarded_1

    guitarded_1 Supporting Member

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    V1 and PI (not P1)
     
  8. doublee

    doublee Member

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    Sorry to be thick but whats PI?

    thanks
     
  9. guitarded_1

    guitarded_1 Supporting Member

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  10. scott1568

    scott1568 Member

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    Again, it depends on the amp. My amp doesn't have a vibrato channel, so I'm not sure about V2.
     
  11. doublee

    doublee Member

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    Duh, sorry.
     
  12. CitizenCain

    CitizenCain Member

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    Well then, it seems, as always, the only thing to do is put it in there and see how it sounds!
     
  13. PSaulino

    PSaulino Silver Supporting Member

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    I'm no amp tech, but.. From what i (think) I know..
    It depends on the preamp /phase inverter design.

    A Tweed amp, 4 input Marshall, and Princeton have some commonality in that the design such that the end result is that the audible clipping DOES come from the Phase inverter.

    That being said, changing that tube can make a difference; the aforementioned CV4024 is one of my favorite tubes in that slot of a Marshall JTM, for instance.

    Paul
     
  14. Guinness Lad

    Guinness Lad Silver Supporting Member

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    With my experience of PI tubes I have found they can add to the overall brightness of the amp and some tubes will really make the amp sing. The funny thing about this is you might think the best tube you have will make the amp sing but sometimes it ends up being a cheap Sovtek. I really think how the amp responds is dependent on the output of the particular tube in question and what type of signal it receives in the first place.
     
  15. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    The PI position can make a huge tonal difference, depending on the amp. You can also change the feel of the amp by going to a different type (12AT7 for a 12AX7, for instance).

    This is a really simple question to answer on your own - just try it.

    By the way, the phase inverter is a fantastic place to use a coveted rare old tube that is microphonic in V1.

    - Thom
     
  16. Buddy Boy

    Buddy Boy Member

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    +1 for Mullard AT7's in PI. Just sent pmt for a pair from a TGP'er. None better in Fenders or Marshall.:BEER
     

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