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Brownfacing a blackface Princeton Reverb clone

Discussion in 'Amp Central Station' started by alnicopu, Oct 25, 2020.

  1. alnicopu

    alnicopu Friend of Leo's

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    Anyone know of it and have any info about making a 6g2(like) amp from blackface clone? Thanks
     
  2. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    The key differences sticking out in my mind are the voltages, the tone circuit, and the overall gain.

    My first priority would be to get the voltage down with a 5Y3. It probably won't get you all the way to the 315V on the 6G2 schematic, but it's a start and I imagine lots of them are running higher than that now anyway.

    The tone circuit is much different, brown Princeton allows some treble boost/cut and that's it, no midrange scoop possible. The tone stack in the Blackface Princeton eats up a lot of gain so they threw in an extra 12AX7 gain stage to make up for it. So if you were to just rewire the tone circuit, you'd end up with way more gain. If that's your cup of tea, then go for it!

    Alternately, you could sort of ape the behavior of the brown tone circuit by turning the bass and treble controls all the way down, and bumping up the volume control to compensate. Then, if you want to brighten or darken the tone a bit, allow the treble or bass control to come up to 1 or 2.
     
  3. Willie Johnson

    Willie Johnson Tele-Meister

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    I have a Silverface Princeton and have wondered about this--what it would sound like with a single tone control like a 6g2 in place of the treble control, and a raw or presence control in place of the bass. A tuxedo blackface with white knobs was hands-down the finest sounding amp I've ever played through.
     
  4. alnicopu

    alnicopu Friend of Leo's

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    Thanks and Yes, the first thing I was gonna do was the 5y3 swap and rebias. Mine has a mid pot so I can scoop and “unscoop” all the mids I want although it never has been a real trebly amp to start with. If the voltages are to high I was already thinking of tweeking the ps resistors. For the tonestack losses I was thinking of just upping the NFB resistor a bit. I cant seem to find any “canned” mods from black to brown on the interwebs and want to go as conservative as possible without too many drastic circuit changes. Ideas, thoughts and other input are much welcomed.
     
  5. King Fan

    King Fan Poster Extraordinaire

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    I’m not sure a mids pot, 5Y3, or NFB tweak are exactly gonna make a PR a 6G2, but they might make it 'less BF.' My PR can get less scooped and less polite if I dial up the mids and dial down the NFB, but it doesn’t really sound like my 6G2.

    FWIW Ceriatone used to make a 'Prinzetone' that claimed to do both — IIRC — at least kinda sorta. I never looked into the how... or how much it actually changed the circuit or the sound,
     
  6. trancedental

    trancedental Tele-Meister

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    The PR preamp & reverb circuit is more similar to to a Brownface 6G!6 Vibroverb Bright Channel, you could easily change the PR preamp / reverb to those values, add the 350 / 70K tap pot & change some coupling caps & dropping resistors. The 6G16 Bright Reverb channel works fine with a Deluxe Reverb power section so should be fine with either the Brown Princeton or Blackface Princeton PS.

    Then use the Brown Princeton cathodyne phase inverter / bias vibrato/push pull output circuit. It doesn't look that much different to a PR. Apart from the 5Y3, I assume the cap can is similar?
     
  7. Mark the Moose

    Mark the Moose Tele-Holic

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    Just build the 6g2 from scratch. It’s a simple build, then you’ll have both.
     
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  8. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    For the record, I fully agree with this. You'd need to rewire it and probably replace some iron to really turn it into a 6G2 -- I was more thinking of ways to steer it in that direction short of gutting and rebuilding it.
     
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  9. King Fan

    King Fan Poster Extraordinaire

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    You're right and I agree with you. If someone's just looking to take a PR in a brownface direction, absolutely. I might also get a variac or build a *vintage voltage adapter* (ie, Rob's bucking transformer) to try 'wall' voltages in say the 112-115 and 105-107 range...
     
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