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Princeton Reverb With Reverb & Tremolo Deleted

Discussion in 'Amp Tech Center' started by robrob, Feb 27, 2020.

  1. robrob

    robrob Poster Extraordinaire Ad Free Member

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    [EDITED after Snfoilhat's input below]

    After realizing how different the blackface Princeton and Princeton Reverb were I decided to do a layout of the Princeton Reverb with the reverb and tremolo deleted. You end up with a fairly simple five tube amp (including rectifier) with a three gain stage preamp vs two for the Princeton.

    The circuit is the same as a Princeton Reverb with the tremolo and reverb set at minimum.

    Of course you can add a Strymon Flint reverb & tremolo pedal and you've got a simple Princeton Reverb.

    Please look it over and let me know if you see any problems. I've gone cross eyed with the circuit review.

    [​IMG]


    [​IMG]

    It would be very easy to build this amp by going with a Princeton Reverb or Deluxe Reverb kit but use the circuit board from this amp to keep the build simple. I have the "Doug Hoffman board files" on my Princeton Reverb webpage that you can upload to Doug's website and he'll build an eyelet or turret board for you.

    More info here: https://robrobinette.com/AA1164_Princeton_Reverb.htm#Delete_Reverb_&_Tremolo
     
    Last edited: Feb 28, 2020
  2. Snfoilhat

    Snfoilhat Tele-Afflicted

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    Cool!

    I'm curious about the effect on gain of deleting the 3.3M:470kish voltage divider that precedes the 3rd gain stage in the stock PR.
     
  3. robrob

    robrob Poster Extraordinaire Ad Free Member

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    The blackface Princeton Reverb bias wiggle tremolo places no load on the guitar signal which is very different than the AB763 blackface signal tremolo. The AB763 load is so high that adding a "tremolo cut switch" is a common mod to add quite a bit of preamp gain.
     
    Last edited: Feb 27, 2020
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  4. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Dang it, I missed that. Yep, the 3.3M resistor forms a voltage divider with the original 470k grid leak to drop 88% of the signal. I've got to plug the 3.3M and cap back into the circuit.
     
  5. Ten Over

    Ten Over Tele-Holic

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    How about if you put a 47K between the 330K and ground and then connect the grid to the junction of these two resistors?
     
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  6. robrob

    robrob Poster Extraordinaire Ad Free Member

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    I was unable to revise the layout and schematic in the first post with the reverb driver 1M resistor, 500pF reverb filter cap, 3.3M reverb mix resistor and bright cap and 470k grid leak resistor.

    Go here to see the updated schematic:
    https://robrobinette.com/AA1164_Princeton_Reverb.htm#Delete_Reverb_&_Tremolo

    I can show the updated layout though because the full size image uses a different name:

    [​IMG]
     
    Last edited: Feb 27, 2020
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  7. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Then we would have a 47k grid leak resistor for V2A which could affect it's overdrive tone. I just decided to go back to the stock circuit to keep the tone as faithful as possible.
     
    Last edited: Feb 27, 2020
  8. robrob

    robrob Poster Extraordinaire Ad Free Member

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    I think I'm going to have to do a Micro version of this amp.
     
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  9. Apache Snow

    Apache Snow Tele-Meister

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    I will just keep my reverb and tremolo thank you.
     
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  10. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Deleting it makes the amp a much simpler build but I do love the reverb and tremolo of the Princeton Reverb.
     
  11. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Alright, I'll be the one to ask: do we need that 330K to ground?
     
  12. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Yes, it's the V2A grid leak resistor.
     
  13. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    aaaah true.
     
  14. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Bill of Materials For Reverb & Tremolo Deleted
    [​IMG]
     
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  15. Burning Fingers

    Burning Fingers TDPRI Member

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    I have done similar to an old factory P.A amp...turned it into a Princeton Blackface circuit AA964 with the tremolo removed.

    There is 1/2 of a 12ax7 going unused but it sounds better to me without that extra gain stage. Also a NFB switch that can give it a bit of a devilish growl with the volume turned up past 7.

    Using a 25 watt rated output transformer helps give a solid and smooth bottom end through a 12 inch speaker.

    I call it my "Princeton Devil"..it can be clean and sweet...but also turn on you when the NFB is disengaged.

    A very easy to construct amplifier and as Rob said..add a reverb and tremolo pedal and you have a Princeton reverb... I never build tremolo or reverb into any of my amps... I save myself the cost and the hassle of inbuilt effects with a decent reverb and tremolo pedal.

    princeton schematic no tremolo.jpg Princeton Devil.jpg
     
  16. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Odd timing. I have a build thread I started in January about a modified Harvard layout. I told a friend today that I am expecting something similar to a Princeton Reverb without reverb or tremolo, and with just a tone knob. Fixed bias, 2x 6v6, V1 & V2 gain stages with NFB, probably going with a 5u4 rectifier. Transformers will be here Monday, and the board is done. Won't have the cabinet done for a couple weeks probably, but I'll be able to plug it into something and hear it next week I hope.

    https://www.tdpri.com/threads/modified-5f10-layout-check-over.999590/
     
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  17. robrob

    robrob Poster Extraordinaire Ad Free Member

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    The Princeton Reverb third gain stage along with the 88% attenuation of the Reverb Mix circuit is responsible for the tonal differences between the Princeton Reverb (with reverb and tremolo at minimum setting) compared to the no-reverb Princeton. A full up third gain stage (with no reverb mix attenuation) would need major preamp tweaking to the point it would no longer be anything like a Princeton amp. This amp is designed to give you exactly what you get with a Princeton Reverb with tremolo and reverb set to minimum.
     
  18. Badside

    Badside Tele-Meister

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    Hmmmmm, never though of that. Might have a bit more "personality" than an simplified Deluxe Reverb sans Reverb without going quite as loud.

    Just for fun... one could wire a switch that bypasses the 3M3 resistor (or just parallels it with a lower value) for a stout gain boost, cause sometimes gain is what the soul needs :)
    Of course, without a Master Volume, that would make it pretty loud!
     
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  19. robrob

    robrob Poster Extraordinaire Ad Free Member

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    As soon as snfoilhat pointed out the voltage divider I thought about a bypass as you describe. A 1M reverse audio pot with a switch (pull volume pot to engage gain) might work well as a variable gain control.
     
  20. OldPup

    OldPup Tele-Meister Ad Free Member

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    How close is what you're describing to a BF Champ? I realize I could look at the circuit and try and figure it out myself. But it's easier to ask the good folks here, some of whom may have already pondered this.
     
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