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Princeton reverb parts question.

Discussion in 'Shock Brother's DIY Amps' started by bigguy12321, Jan 2, 2019.

  1. jsnwhite619

    jsnwhite619 Friend of Leo's

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    This thread came at a perfect time - describes my current situation entirely. Can you build a Princeton; what is it that REALLY makes it a Princeton; what benefits from modifying without losing the feel; and I have been told that the only thing that changes when I swap amps is if there is reverb or not - I basically sound & play the same through everything.

    My initial research has me thinking to stay with a GZ34 to not deal with extra current draw concerns. Probably the Hammond 290CAX PT - 275v/315v, 115mA - that I already have and like. First OT choice is their 1750e 15 watt 8k that I already have and like. I've learned on my Vibrolux that combo can stay relatively clean pretty high up with the right bias and voltage.

    He plays a humbucker bridge Tele and hot neck pick up, so I'm thinking to keep that in mind for any humbucker/Princeton mods - maybe lower V1 bias cap?

    Sent from my XT1585 using Tapatalk
     
  2. Wally

    Wally Telefied Ad Free Member

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    Jsnwhite619, in your situation I would plan on going to the max with the first stage of filtering if you are concerned with keeping the low end firm and punchy. 50mfds is the max for the GZ34, iirc. Of course, this definitely changes the ‘feel’ of the amp. Smaller PI coupling caps might be advisable, too, if he drives the amp hard. Again....this also changes the feel. So does changing the input preamp bypass cap. Every changes changes the feel and sound, imho.

    As for what a particular player sounds like from amp to amp??? Well, there are some amps that cannot possibly sound like other amps, ime....no matter who is playing them. BF/SF Reverb amps??. At some volume levels, they all sound very similar. They differ when pushed hard, ime. On such amps, each player will find their own self somewhere....and sound very much the same from amp to amp...ime. Someone else could walk up to the amp while you are playing and change things so that your playing might not sound like what you would choose when setting up the amp.
     
  3. jsnwhite619

    jsnwhite619 Friend of Leo's

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    That's why I don't play those kinds of amps... ;-) Taking things a bit too literally, but I was just agreeing with what has been said by a few others already -- I tweak and work guitars and amps that I play to give me pretty similar sounds across the board. The main reason I use different guitars live is generally for alternate tunings & slide playing. If I pick up a hot guitar, I adjust my volume & attack to get the sound I want. My friend who builds guitars and winds pickups quit using me to test out any new stuff because he said I made everything he handed me sound like a Telecaster. :D
     
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  4. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Back to the transformers, I just found this where Hammond increased the specs of their 290AX PT. Spec sheet says this version is from May of 2018, so if you wanted this one, you may need to inquire about the stock supply and which version is it.

    290AX.png
     

    Attached Files:

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  5. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I've gone through some old TDPRI Princeton Reverb posts. I've never owned one, so I have no direct experience. Chiming in on a lot that has already been said - under powered PT, voltages too high, etc., I found another Hammond PT that may be a good option, but I can't find anywhere that sells it. It's their Harvard model. It looks like they've discontinued the 290CAX with the dual secondaries and beefed up the 290AX and created the 290HAX. Both are 100mA vs 115mA of the CAX. But, both have 3A 5v taps that can handle a 5u4, and both have a little more on the heaters. But, the HAX has a 50v bias tap as well, and both have center tapped heaters. So, bonus points to the first person who finds the HAX available online!

    290hax.png
     
    Last edited: Jan 4, 2019
  6. Fuga Mante

    Fuga Mante TDPRI Member

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    ClassicTone offers a PT with 100mA of current that is a direct replacement for the Princeton Reverb chassis (the classic chassis), that helps to ease the strain on the secondary, which produces less heat, which is kind of nice; but what having 100mA available in your Power section is really neat for is to be able to change the tube complement a bit in there —6L6, 5881.

    I built a retrofitted an AA1164 Princeton Reverb on a '78 push-pull carcass, and went ahead and upped the filtering (40/20/20/20), along with the trannies and the diode, the rest is stock in design but new in construction. The signal caps are mustard Sozo's, for that smoothness only those can provide; added a resistor, believe it was a 470k onto the grid of the last pre-amp tube V4, the phase-inverter, per Rob Robinette advice, to handle the distortion a bit, it has improved the amp IMO. A trim pot for the negative voltage control, and metal-oxide resistors for the filtering and power nodes, and carbon-comp for the rest. A Mojo cab (a great investment if you ask me) and an Eminence Ragin Cajun speaker, for louder volumes within the 10" realm, couldn't be happier.

    A modernized Princeton Reverb, with the still inefficient cathodyne PI, but sturdier performance everywhere else. As a pedal platform, it can't be beaten; I've sparred with a 50watter Marshall, half-stack and all, and the other guitarist was baffled at the crisp and smooth decay of the little 10-inch speaker amp distortion. It's a beast if I say so myself. The form factor and interesting design limitations of a Princeton with a Deluxe Reverb power section —you know why Fender never made this amp? Because they wanted to charge you extra for an additional (and rarely used anyway) channel and a 12" speaker in the Deluxe. Then you still have the bias-vary tremolo with a retrofitted Princeton, which Fender now does in their '64 Reissue Deluxe Reverb they hand-made, go wonder.

    When approached from a modern stand-point, a Princeton Reverb is the mightiest platform to scale-up into the perfect sound/features vs size/convenience on the whole spectrum of Fender amps out there, IMO. This can also be achieved through plenty of different means too, so it's very "personable". It's a great design, that now-a-days is a breeze to make better without changing the overall tone and performance of Fender's little wonder.
     
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  7. Wally

    Wally Telefied Ad Free Member

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    Fuga Mante wrote: “a Princeton Reverb is the mightiest platform to scale-up into the perfect sound/features vs. size/convenience...”

    Randall Smith wrote the book on that one...in the early ‘70’s. It is amazing to look into the back of a Princeton
    Reverb cab and find 4x6L6’s!! Then, you lift it and understand that it no longer is a little amp.
    Fender went the other direction...they maintained the Princeton circuit albeit without the trem effect and put it into a
    Champ-sized cab...called it the Super Champ.
     
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  8. jsnwhite619

    jsnwhite619 Friend of Leo's

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    That Tweed Princeton Reverb I built earlier this year is the ONE amp I wish I still had. I used a 100mA Hammond PT, made a cap board with all 22uf F&T on it, and the cab was a full 10" deep at the bottom and 1" taller for a 12" speaker, a Cannabis Rex. Best amp I've built, and volume to spare as far as I'm concerned.

    Sent from my XT1585 using Tapatalk
     
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  9. magicfingers99

    magicfingers99 Friend of Leo's

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    its a combination of design choices and materials. 15 watt tube amp
    with a gain stage after the reverb. The cabinet size influences the sound as well
    and the speaker size

    there are also a bu**load of mods out there to change it up a little.


    https://www.mojotone.com/kits/BlackfaceAmpKits_x/Mojotone-Blackface-Princeton-Reverb-Style-Amp-Kit_2

    per advert


    The Mojotone Princeton Reverb style amp is a 12-15 watt miniature giant that comes stock with a Jensen C10Q 10” 35 watt speaker and (2) 6V6 power tubes. Like the original Blackface era Princetons, the Mojotone amp has the added gain stage after the reverb that pushes the amp to a thicker level of saturation when the amp is pushed. This effect, mixed with the smooth compression of the 6V6 tubes and the classic tone of the Jensen speaker makes for a creamy and soulful tone with a ton of character.


    The amp has one channel with two inputs. Input 1 is slightly hotter where input 2 is just a bit more mellow. The advantage here is the ability to plug in a guitar with single coils to input 1 and a guitar with humbuckers to input 2 without having to worry about making manual adjustments to the amp’s volume level when switching guitars. The control panels from left to right reads “volume, treble, bass, reverb, speed, and intensity.” This means you get all the unique tonal qualities of the classic AA1164 circuit as without having to spend hours dialing in the right sound with too many knobs. This amp is designed to give any guitarist a pure, articulate tone that is appropriate for any setting and handles a pedal chain beautifully. Just plug your guitar in and you’ll be jammin’ “Surfin’ USA” in no time.


    We offer a completely hand-wired Princeton Reverb style amp assembled by our expert builders right here at Mojotone headquarters. Our in-house technicians have an extreme attention to detail and take great pride in their work -- our builds are 100% guaranteed.


    this one is probably similiar, but offers lots of mods/choices

    https://www.tedweber.com/6a14-c-kt

    find out if he wants a black face or a brown face, I beleive the circuits are different

    http://ampwares.com/amplifiers/fender-blackface-princeton-reverb/

    has schematic diagrams
     
  10. magicfingers99

    magicfingers99 Friend of Leo's

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    Actually the Princeton wins if you count separately all those 3,000 takes of each Steely Dan song recorded and erased before the final version was settled upon.
     
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  11. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Oh yeah, the NFB mod I did was completely with it. I did a 3 way switch, stock, maybe double stock, and off. Anyone who has a PR and wishes it was a little brighter or just needs a little more volume, doubling the NFB value made a huge difference. After I got used to it, the stock setup just sounded muffled and choked. Really helped at low volume to brighten it up.

    Sent from my XT1585 using Tapatalk
     
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  12. TelZilla

    TelZilla Friend of Leo's

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    If he wants a Princeton Reverb, I'd just build him a Princeton Reverb. Is there a reason not to? Budget? Other?
     
  13. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    Another thing that makes a PR a PR is the 1k screen node resistor. It lowers the voltage to screens more than a choke, which is how the vintage PRs got away without screen grid resistors.

    I've built 3 now with up sized iron, GZ34, increased preamp voltages (with the cathodyne moved up a node also, and an efficient 12" speaker. To me, they all sounded better than stock, and very giggable.

    On the last one, I added a 100pF bright switch, and a 6.8k to 33k mid resistor switch. The customer likes it a lot.
     
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  14. Uncle Daddy

    Uncle Daddy Tele-Afflicted

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    I built mine with the Stokes mod, C12q, bigger trannies etc, and it makes a PRRI sound like a toy.
     
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  15. driprail

    driprail TDPRI Member

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    The Princeton Reverb is unique in that many of the components are operate at or near their limit. Putting a GZ34 into a PR will bring the B+ up by 40V, which is perfect for a pair of vintage RCA 6V6's, but, in my experience, a Russian or Chinese tube will loose whatever tone it had in about a month.

    All of my Fender amp builds are based on de-modding BF and SF amps and this is what my scratch build Princton Reverb would look like:
    - Get the right Accutronics reverb spring
    - Use a Mullard GZ34 rectifier and vintage RCA, Sylvania JAN, Tung-Sol 6V6's
    - Use Mullard, Telefunken, Amperex or RCA 12AX7s (7025) and 12AT7
    - Pay particular attention to the reverb driver and recovery tubes (roll them for sound)
    - Replace the ****ty 10" speaker with a JBL D110 or E110 reconed to 4 ohms

    Basically, these changes result in hearing the tubes breakup rather than the speaker farting. The JBL speaker is heavy, but incredibly efficient, resulting in a lot of volume from very small package. At 4 ohms, it wants to pull 2x more current through the output transformer, but the power transformer limits the overall current, and the sag from the GZ34 gives a very natural compression.

    https://www.tdpri.com/threads/gz34-in-5u4gb-fender-circuits.327195/
     
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  16. bigguy12321

    bigguy12321 Tele-Meister

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    Ok, O.P. here. I have really enjoyed this discussion and gleaned a bunch.

    I have not heard back from the guy about the amp so... Onward and upward.

    From what I can gather, there are 2 distinct camps here. Those that are say build it as stock and those who believe that the design can be improved upon. Checking the interwebs for videos of both examples is fruitless. They all sound similar over the airwaves and there are many good and... not so good players demoing both into many different types of video recorders.

    So.

    I think for me it comes down to the basic circuit with a smallish P.T. (100ma or less), multi tap O.T. for flexibility of speaker choice. Efficient 10in speaker... or 2... Decent quality caps and resistors, with room for a couple mods in the future.

    Since I'll probably never have an original, I would have to make what I like. To be honest, I sound the same through whatever amp I play anyway so true period correct is kind of wasted on me.

    If I happen to get another request from someone to actually build one this discussion will serve as an excellent guide.

    Thank you to all who have chimed in. It has been fun.

    Please feel free to continue this discussion. More info is always good!

    a
     
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  17. Kevin Wolfe

    Kevin Wolfe Tele-Holic

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    I’m interest in this discussion. Planning a PR build and want to end up right between very original and super efficient.
     
  18. jordan86

    jordan86 TDPRI Member

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    I know this is an old thread...curious what PT’s you guys with the “big iron” went with? I am building a Princeton here soon.

    Looking at the Hammond 290AX or the Allen TP25 to allow 5881’s.

    Planning to due the Allen TO20 as well.

    Would love to know what you guys chose.
     
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