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5E3 phase inverter - convert to Long Tail Pair

Discussion in 'Amp Tech Center' started by chester442, May 5, 2017.

  1. chester442

    chester442 TDPRI Member

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    Hello Everyone,
    I have an amp I built, that is currently a single input, single channel 5E3 derivative, with a simple volume and tone circuit. The two red Jupiter coupling caps are .022uf and the rest is fairly true to the 5E3.
    I would like to try replacing the existing phase inverter with a long tail pair circuit.
    I'm hoping to do this as simply as possible, building on what's already there.
    In the photo, you can see that I have one unused triode at V1 (12AY7), if that helps.
    This mod is for my own curiosity to hear what happens when you take out the typical 5E3 PI induced distortion from the equation. I'm not in need of more headroom. Just want to hear the impact on overall character.
    Please advise, and if possible, direct me to a layout drawing of how the changes to the board might look.
    Thanks very much for your time and knowledge! my5e3guts03.jpg
     
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  2. robrob

    robrob Poster Extraordinaire Ad Free Member

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    It would be pretty bizarre to see V1B & V2B married together as an LTP so I'd move V2A over to V1B and use all of V2 as the LTP. Take a look at the 6G3 brown Deluxe schematic and layout. This could get messy.
     
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  3. Wally

    Wally Telefied Ad Free Member

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    IMHO, more of a sonic difference might be had by installing an option to go from cathode biased to fixed bias. It certainly would be much simpler.
     
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  4. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I talked to a guy a few weeks ago that had done it, but his level is way beyond mine, so I had to do a lot of "smile and nod" and pretend I was following what he said... As he described it afterward, "turned it into a real screaming demon".
     
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  5. Wally

    Wally Telefied Ad Free Member

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    It would interesting to know whether or not he established a negative feedback loop when he changed to the LTP. IF not, that would explain the 'screamin' demon' description.
     
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  6. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I think he made it single channel and used both halves of a 12ax7 for the phase inverter.....if I remember correctly. Does that sound like it is on the right track?
     
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  7. Wally

    Wally Telefied Ad Free Member

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    I certainly would be interested in listening to some carefully recorded---all else the same--- before and after clips of the change from cathode to LTP inverters. And...I would want to know if there was a NFB loop in place with the LTP...just for grins, it would be a good time to install an adjustable NFB loop...or switched from in to out.
    The 6G3 Deluxe would be an interesting amp in which to place a cathode to fixed biased switch. then you could have a simple preamp closer to the 5E3 than to the AB763 with a LTP and 2 x 6V6's with an option for that biasing...which would affect how that amp sounded. Now, I want one. I Didn't get to keep the only 6G3 I have had very long. I liked it. However, it had to stay with the mint '63 Strat with which it was bought in 1963.
     
  8. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Chester, changing to an LTP will require major surgery to your circuit board. You'll have to move the V2A circuit over to V1B including moving the load resistor and coupling cap. You'll then have to add a couple of turrets to support the LTP components.
     
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  9. Teleguy61

    Teleguy61 Friend of Leo's

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    Honestly, if you want a different amp, build a different amp.
    It will be simpler.
     
  10. jmp81sc

    jmp81sc Tele-Meister

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    If I were you, I would either build a new amp or at least build a new board. Wally's idea of A 6g3 with switchable cathode/fixed bias would be the ticket. Two amps are better than one :)
     
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  11. dougstrum

    dougstrum Friend of Leo's

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    It could certainly be done...Use a 12ax7 for the inverter and
    the other 12a?7 for preamp. You'll end up with a cathode bias
    single channel 6g3.
    Fun experiment if you like soldering, bet it would sound good~
    but probably no better than what you've already got. I personally
    like the 5e3 cathodyne inverter.
     
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  12. chester442

    chester442 TDPRI Member

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    my-new-amp-layout.jpg
    Here's what I came up with. I'm hoping the 12AX7 (instead of 12AY7) in V1 will supply some of the gain lost by removing the driver portion at V2 (to make room for the LTP).
     

    Attached Files:

    Last edited: May 10, 2017
  13. chester442

    chester442 TDPRI Member

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    Thanks. I'm not planning on using my existing amp. This is a scratch build.
     
  14. chester442

    chester442 TDPRI Member

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    Yeah, I have the parts, so this would be a separate amp.
     
  15. chester442

    chester442 TDPRI Member

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    Thanks, everyone, for the good info!
     
  16. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I how it all works ok. After talking to the guy that gave me his advice on it, I've wondered how it would sound, but it was a little beyond my level to sort it out. What you are doing seems to match up with what he was saying now that I see it worked out. After seeing so much about 5e3 phase inverter distortion, I am curious to how this works out.
     
  17. chester442

    chester442 TDPRI Member

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    Yep, that description (cathode bias, single channel 6G3) is what I was thinking. For what it's worth, I play a lot of finger style, working the volume knob on the guitar, with the amp breaking up. I love the squishy, compressed power section of the 5E3, especially when the volume knob is rolled back, and the signal is cleanish, but singing. What I'm not that into is the splatty bursts that happen in the transition zone, before full crunch comes on. Maybe that is helpful info?
     
  18. chester442

    chester442 TDPRI Member

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    Sorry, I wasn't clear about building this as a new amp (or at least a new board). I have the parts to do a second amp, and the existing amp is fine, as is. Thanks.
     
  19. chester442

    chester442 TDPRI Member

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    Yep, definitely. This would be a separate amp.
     
  20. Wally

    Wally Telefied Ad Free Member

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    Just curious....with that 'splatty bursts' description of the overdrive in your 5E3 in mind, I have to ask what guitar you play that yields that splatty burst effect? I ask because ime I have found that Fender single coils do not push an amp smoothly into that overdrive whereas a Gibson P-90 or a humbucker will yield a smooth overdrive. This is, imho, why most people who play 'small' single coils use boost and/or overdrive pedals to get the amp to act as it does with a 'bigger' pickup.
     
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