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Princeton Reverb head build with Deluxe PT and OT...

Discussion in 'Amp Tech Center' started by Jerry Bee, Aug 13, 2017.

  1. Jerry Bee

    Jerry Bee TDPRI Member

    Age:
    45
    12
    Nov 11, 2016
    Hamburg
    Hey guys,
    I got a good deal at modulus amplification UK...a princeton reverb chassis with faceplates included:

    http://modulusamplification.com/Blackface-Princeton-Reverb-Chassis-Faceplates-P5266372.aspx

    But what I did not realised is that it has the mounting dimensions for the deluxe PT and OT, which is a good thing...I guess :)
    So I could build a beefed up PR now.

    Now my question is, should I build it stock or do you recommend any mods like Stokes, PaulC etc.?

    My plan is to build it with a switchable raw control, a pre pi mv and run it through a 12" speaker like a 12a150a...So I could use it for practicing, recording and gigging.

    Cheers
     
    Last edited: Aug 13, 2017

  2. Dacious

    Dacious Friend of Leo's

    Mar 16, 2003
    Godzone
    John Stokes doesn't recommend his mod with stock output transformer. Using the Deluxe transformers is a no-brainer in my opinion, or at least a higher rated power transformer as the Champ P/t gets pretty hot more so from the heater rating being marginal. You're not doing vintage so upgrades are in order. You do have to watch the power you run, I think.
     
    Jerry Bee likes this.

  3. Bendyha

    Bendyha Tele-Holic Ad Free Member

    967
    Mar 26, 2014
    Northern Germany
    The PaulC mod is flawed. It is based on incorrectly taken measurements. One can do a fixed bias phase inverter mod, but don't use the resistors that PaulC's mod recommends. If you want to do it, read more about the correct method here; tdpri. #post-7796029
     
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  5. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    I'd throw a 470k grid stopper on the phase inverter grid. It won't affect the clean tone but will sweeten heavy overdrive.
     
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  6. Jerry Bee

    Jerry Bee TDPRI Member

    Age:
    45
    12
    Nov 11, 2016
    Hamburg
    Hey Rob,

    I want to do your pre pi mastervolume with 1M pot anyway...
     

  7. danlad

    danlad Tele-Meister

    158
    Mar 24, 2015
    Here and there
    I wholeheartedly second the grid stopper for that PI
     
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  8. Mart the Hat

    Mart the Hat Tele-Meister

    450
    Feb 11, 2013
    Edinburgh, Scotland
    You might already have considered this, but pre-PI master on a Princeton Reverb has limited usefulness compared to some other amps. I've tried it on mine, it doesn't really get any useful dirt and doesn't get you anything resembling the cranked amp sound, but for whisper-volume home use it still wakes up the preamp a little and gets the reverb working a touch better than if you have a single volume set somewhere below 1. If that's all you want from it it can still be worth having though.
     
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  9. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    Yea, with low-gain preamps you'll need a boost pedal to get some preamp distortion so you can turn down the master volume and still have dirt.
     
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  10. Jerry Bee

    Jerry Bee TDPRI Member

    Age:
    45
    12
    Nov 11, 2016
    Hamburg
    So a post pi mv would make more sense? Then the preamp would drive the pi more.
    I have good results with the post pi mv on my jtm-50 plexi Clone or does it depend on longtail vs cathodyn pi?

    I just want to lower the overall volume a tad to get a slightly overdriven sound for rythm work and then hit it with a booster or engage the raw control to let the beast roar and scream...

    An alternative would be to build a one channel deluxe reverb
     
    Last edited: Aug 13, 2017

  11. jhundt

    jhundt Poster Extraordinaire

    Age:
    63
    Mar 23, 2003
    Netherlands
    no, the pre-amp will NOT drive the PI to any kind of useful distortion. The design of the cathodyne PI does not permit that. There is no gain added in the PI, and there is no advantage to using a post-PI master volume for that reason.

    I have a Princeton Reverb in which I have installed a Deluxe Reverb power transformer, and an upgraded output transformer that is even stronger than the Deluxe Reverb OT. It is a very fine-sounding amplifier, but it does not create a lot of overdrive distortion. And it is very, very loud.

    I played around with Stokes and PaulC mods, but I realized that the Fender PR is a very good amp just the way it was built - except for the weak transformers.

    I have considered the grid-stop resisitor or MV as described by Rob R, but because I rarely play with heavy overdrive or distortion I have not yet found it necessary. In fact I was happiest when I removed all my mods - except the upgraded transformers - and let the Fender sound like a Fender.

    I also have a PRII which I rewired as a single-channel Deluxe. It has a pre-PI master volume that works just fine. I tried a post-PI but did not feel that it added anything for my style of playing. (I do not play heavy blues-rock lead guitar)

    I would suggest that you make a very nice Princeton with upgraded power- and output transformers, and learn how to enjoy that amp. It may require pedals for low-volume distortion and overdrive - but that's an easy thing to do. Much easier than trying to make a well-designed amp do something other than what it was designed for.
     
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  12. Jerry Bee

    Jerry Bee TDPRI Member

    Age:
    45
    12
    Nov 11, 2016
    Hamburg
    Thank you jhundt, that sounds very reasonable and I will do it that way.

    For dirty sounds i have my tweeds...
     

  13. jhundt

    jhundt Poster Extraordinaire

    Age:
    63
    Mar 23, 2003
    Netherlands
    anyway, you can always do more mods later, after you have built and tested the amp. Please let us know how your build works out. There are lots of Princeton-lovers here!
     
    Jerry Bee likes this.

  14. Jerry Bee

    Jerry Bee TDPRI Member

    Age:
    45
    12
    Nov 11, 2016
    Hamburg
    Found a nice power transformer, originally for a 5E3 at the dutch tone factory, which is a bit over specs, see attached datasheet. But it will fit the mounting dimensions 100% and gives enough juice with 120 mA and 3A for the 5U4GB.
    I heard that Mabel Audio is the chinese tranny supplier for Weber and I only paid 69 Euro for it. The Hammond and TAD Deluxe pt are over 100 Euro. They have the 50 V bias supply, which I don't need anyway.

    First step for the build is to adjust the housing and I fished a mint and light birch ply cab in the bay.
    The height of the chassis cutout is 1/2" too tall, but the width will fit for the PR chassis as you see.

    5e3 PT-2.jpg

    DSC_0134.JPG
     
    Last edited: Aug 17, 2017 at 2:47 PM

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