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Technical preamp question from a dummy....

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  • Technical preamp question from a dummy....

    OK... so I bought a Tung-Sol to spice up my preamp in my Crate Vintage Club 60 2x10. I realized that the effects loop tube was a 12AU7 which I want for my PI and since I don't (usually) use the FX loop, I thought I'd swap it in for ****s and grins. OK...

    If you are looking at the circuit from the bottom (it's a combo) from the back, it looks like this:

    [input tranny] (tube)--space---(tube) (tube) (tube) [output tranny]

    The tube closest to the input was hotter than the rest, so I assumed it was the V1 tube, BUT that tube is further away than the rest and I know PI's are worked very hard, so I thought maybe the circuit had them in the opposite orientation. I swapped in the UA7 at the last tube by the output and the sound was very low, tinny and almost non-existent. Soooooo, I tried the opposite side and same thing. Obviously the tube is shot... However, I discovered a Groove Tube AX7 in the last slot by the output tranny and stuck it in the second to last slot. OK.... Putting the Tung-Sol in the (assumptive) V1 slot, made all the harshness go away that the stock Sovteks were delivering, making me rethink needing new output tubes or really doing any work on it right now.

    Just wondering, am I correct (having no access to a wiring diagram or schematic) that the order is:

    [input] (V1)----space----(V2) (V3) (PI) [output] ??
    Last edited by IanBallard; 09-24-2011, 03:52 PM.

  • #2
    Re: Technical preamp question from a dummy....

    Well, the first mistake you made in this post was failing to provide that make and model of the amplifier. However, IN GENERAL, the V1 tube is closest to the input, and the PI is closest to the power tubes. That's not necessarily the case in every amp, but it is that way in a lot of them.

    P.S. Lower end Sovteks have never gotten along with me. You really should get rid of those immediately.

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    • #3
      Re: Technical preamp question from a dummy....

      Originally posted by misterwhizzy View Post
      Well, the first mistake you made in this post was failing to provide that make and model of the amplifier. However, IN GENERAL, the V1 tube is closest to the input, and the PI is closest to the power tubes. That's not necessarily the case in every amp, but it is that way in a lot of them.

      P.S. Lower end Sovteks have never gotten along with me. You really should get rid of those immediately.
      Edited for provision of make and model.

      The power tubes are actually situated closer to the input, near the rear of the amp, so that's why I was confused:

      __________________front controls____________________
      [input] (tube)...........(tube)(tube)(tube) [output]
      ............{power}{power}
      ____________________rear__________________________
      Sort of like that.

      It would be nice to have a phone with internet access so I can post actual photos.

      Anyhoo, the sound difference is AMAZING just swapping out tubes. Now I may just get two more Tung-Sols and a JJ ECC82 for the PI!
      Last edited by IanBallard; 09-24-2011, 04:14 PM.

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      • #4
        Re: Technical preamp question from a dummy....

        When you say input, are you talking about the instrument input or the power transformer? There's no such thing as an input transformer.
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        • #5
          Re: Technical preamp question from a dummy....

          Originally posted by Agileguy_101 View Post
          When you say input, are you talking about the instrument input or the power transformer? There's no such thing as an input transformer.
          There is actually, but they're not used in guitar amps.


          Carry on.
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          • #6
            Re: Technical preamp question from a dummy....

            Originally posted by Agileguy_101 View Post
            When you say input, are you talking about the instrument input or the power transformer? There's no such thing as an input transformer.
            Power transformer. There's only two transformers. What's so hard to understand here? You're just dabbing in semantics dude.

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