1. The Gear Page is run by musicians for musicians. We listen, we learn and if we misstep we are not afraid to do the right thing. We proposed some changes to the Emporiums. Based on feedback from members, we have decided to not go ahead with those changes. However, it has also highlighted that we need some community input into what is working and what is not working for members here. Primarily focused on the Emporiums, we'd like input on your thoughts about TGP and how things work in the Emporiums for you and how you'd improve them. The discussion thread on the is here!

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novice question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mojoworker, Jan 29, 2012.

  1. mojoworker

    mojoworker Member

    Jan 22, 2012
    i am new to the site. what does PI stand for in reference to amps/schematics?

    thanks -

  2. Blue Strat

    Blue Strat Member

    Aug 2, 2002
    Sterling, VA (not far from Washington DC)
    Phase Inverter, the preamp tube located closest to the power tubes.
  3. TweeDLX

    TweeDLX Member

    Mar 24, 2008
    Port Angeles, Washington
    Represented on a schematic in the following ways. The first is a cathodyne PI, and the second is a long tailed pair. Fender used cathodyne in most of their tweed era amps, and switched to the LTP style in the black face era. The Princeton is the only Fender that comes to mind still using a Cathodyne PI. Most Marshalls use a LTP type PI.

    Cathodyne PI

    Long-tailed pair (LTP) PI

  4. VaughnC

    VaughnC Supporting Member

    Jan 4, 2002
    Phase Inverter: its purpose is to take the signal from the preamp and output two signals that are 180 degrees out of phase...which is required to drive a push/pull type power output stage. Push/pull output stages always have an even number of tubes (or transistors). However, single or parallel tube (non-push/pull) output stages don't need a phase inverter stage so those type of amps don't have one...and they can have odd or even number of output tubes (or transistors).
    Last edited: Jan 29, 2012

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