1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

What is it about the Princeton Reverb that makes it such a good platform for mods?

Discussion in 'Glowing Bottle Tube Amp Forum' started by theprofessor, Jun 14, 2020.

  1. theprofessor

    theprofessor Poster Extraordinaire

    Posts:
    5,395
    Joined:
    Aug 8, 2016
    Location:
    Chattanooga, TN
    It seems to me that the Princeton Reverb is especially suited for mods of various sorts. A common one that I like is to use a Deluxe Reverb-sized output transformer. Then there is adding a mids pot or the Stokes mod. I am also a big fan of the mids pot. Or using a PT (and OT) that allows for running 6L6s or 5881s. Or even just putting a 12" speaker in a stock Princeton Reverb. Most all these that I've heard have yielded great results. Of course there is the discussion of whether a Princeton Reverb with a different output transformer is "really a Princeton," or whatever, but that is not the point of focus here.

    Historically speaking, these sorts of things formed the aegis of things like the Paul Rivera Super Champ or the Randall Smith Mesa-Boogie line. And this is particularly interesting, since the Princeton Reverb is the blackface/silverface amp that shows the most direct tie back to the tweed line, but it seems also to have offered the possibility of being the most forward-looking at the very same time.

    So what, in your opinion, are the key features of the Princeton Reverb's topology that has historically made it such a great platform for modifications like these, even leading to a whole new line of amplifiers in some cases?
     
  2. Wally

    Wally Telefied Ad Free Member

    Posts:
    37,276
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    I would not place what Randall Smith did into the classification of being a modded Princeton Reverb since what Smith wrought was not a Princeton Reverb other than with respect to the cab. He chose the Prin Rev for the cab size.....until Fender stopped selling him new Princeton Reverbs that were simply being gutted for what was essentially a new build.....bigger trannies, 6L6’s with a LTP PI and output section more like the larger Fender amps. The preamp was based on the AB763 preamp, and that preamp came about before the BF Princeton/Princeton Reverb was ever designed. Smith added a gain stage to the front end for the high gain input...making the topography something closer to a 5F6A than the BF topography in the lower gain. I will never forget the BF Princeton Reverb that came around in the ‘90s with four 6L6s along with the big trannies jammed into that small chassis. It is remarkable what some folks will do.
    that aside.... All of the BF/SF circuits are excellent platforms for mods. In fact, Howard Dumble created the most valuable amps ever built from just that beginning....modding AB763 based Fenders. Those vintage Fenders were well-built and offer excellent accessibility to the circuits making mods easier than they would be with other makes of amps...ime. Given that and also the excellent Sonics of the original circuits, it is easy to understand why there have been people modifying these amps for more than 50 years.
     
  3. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,744
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Great question. Useful question. Question near and dear to my heart. :)

    Not to play Dan Akroyd to your Jane Curtin, Professor, but *in some ways* the PR is *not* a great platform for mods. Rob's PR page is almost the antithesis of his 5E3 page -- it's kind of a long list of things *not* to do to the amp, and a short list of (mostly non-sonic) mods.

    And many many PR mod threads are like: "Tried a bunch of circuit mods, kept a couple, don't use 'em all that much."

    But it seems to me you're not talking about 5E3 style *circuit* mods. The PR was a highly-evolved amp, sort of a pinnacle of one branch of Fender evolution. And that's why the kind of mods you mention are different. Few people do bigger speakers in 5E3s, or bigger transformers, or output tube swaps, and few people do coupling / bypass caps in PRs...

    And that gets to how you "mod" a nearly perfect amp. The PR, as @Wally always notes, was on a distinct branch of Fender evolution that came through the 5F11 and 6G2 and went on the the Rivera Super Champ. It's not much like all its many AB763 cousins. So your 'distinctive features' gotta be those that Rob lists: the PI, absence of choke, output tube bias-wiggle tremolo. (Some would say its defining features also include the *absence* of AB763 features like big iron, big speakers, big tubes, dual channels....)

    So a 'nearly perfected' little amp says to many (especially gigging musicians): "Make it bigger." Bigger iron, bigger speakers, bigger tubes, the Stokes mod -- let's see if it can play with the AB763s. These are all popular but except for Stokes they're not circuit mods, and Stokes isn't actually all that popular: Mr. Stokes himself stopped suggesting it.

    There are a few sonic mods, yes: a PI grid stopper makes the drive even sweeter. A mids pot can 'correct' the PR's distinctive scoop and large tone-stack signal loss, but my reading of *most* (not all) reports is that many people use theirs sparingly, and usually at low settings. NFB cuts get the same general vibe, seeming less drastic and popular than in other amps.

    So I'll answer the question this way: The PR is a great platform for "building out from" because, for its goals, it's a 'nearly perfect' amp. So in fact you don't want to alter the *topology* very much when you build out.
     
    Last edited: Jun 14, 2020
    theprofessor and robrob like this.
  4. schmee

    schmee Doctor of Teleocity Silver Supporter

    Posts:
    12,679
    Joined:
    Jun 2, 2003
    Location:
    northwest
    I think mostly it's because it's a smallish one channel design which is readily given more headroom with simple mods. Mesa Boogie .....right? Not all amp designs work well to get more headroom out of.
    I've tried a ton of mods on the PR design. Probably built 5 of them over the years. Still have my original hacked up '70 PR which morphed into this:
    [​IMG]
     
    Wally, theprofessor and robrob like this.
  5. robrob

    robrob Poster Extraordinaire Ad Free Member

    Posts:
    7,968
    Joined:
    Dec 29, 2012
    Location:
    United States
    Nicely said King Fan. The PR is almost perfect. Add the PI grid stopper and it is perfect.
     
    Javier668 likes this.
  6. Wally

    Wally Telefied Ad Free Member

    Posts:
    37,276
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    Nice looking amp, schmee. I have a lot of old cloth from organs...which that cloth of yours resembles. It goes well with the alligator tolex, too. I am sure the Sonics are even more impressive than the great cosmetics.
     
  7. theprofessor

    theprofessor Poster Extraordinaire

    Posts:
    5,395
    Joined:
    Aug 8, 2016
    Location:
    Chattanooga, TN
    Thank you, Wally, for this description. Given what you lay out here, it is incorrect for me to include the Mesa-Boogies in my narration. And it sounds like the AB763 has been a playing field for much new amplification design.

    I'll respond to this below Rob's comment that I cite next:

    @King Fan , you said all this so well. You're right that it depends on what we're calling mods. I'd say increasing the filtering to an initial 40uF reservoir cap from a spec'd 20uF one is a mod (the JJ cap can I used has an initial 40uF section). I'd call adding a mids/raw pot is a mod, as is adding the phase inverter grid stopper and slowing down and intensifying the tremolo (the last two are not necessary, but it they are nice). But as you say, those are not so many mods that affect the circuit. Many of the others I mentioned are bigger in scale, like transformers and speakers.

    You mention the 5e3 and all the mods listed for that amp, whereas the list for a Princeton Reverb is generally much shorter. Piggybacking on what @robrob says above: it seems to me that is because the Princeton Reverb is nearly perfect. The reason there is such a long list of mods for the 5e3 is -- in my opinion -- that it is not a great amp (ducking). There are so many things to do to that thing to optimize it, and it is finicky about speakers and cab size, and you've got the whole interactive controls thing. It's just an unwieldy beast that needs channeling. For many, that's what makes it so great. That is not my opinion (though after I finally perfected the one I built and got it sounding like a million bucks, I realized it was somebody else's great sound and not mine, so I sold it; the fellow who bought it thought it was better than some high-end boutique ones he'd played).

    So maybe we continue to toy with the 5e3 because of its flaws (this is my opinion, not the opinion of others), while we continue to toy with the Princeton Reverb because it is already almost perfect, and we feel we can make it "perfecter."

    And that brings me around to @schmee 's comment on the size. In the last decade or so (maybe longer?), folks have been looking for a grab n' go that can hang with a big-time band. So if you take the Princeton Reverb as your basis and put a bigger output transformer in there and a 12" speaker (which can fit into a standard PR-sized cab) and maybe a few other things, you can do that. So the impulse to build out a Princeton Reverb a little bit must have something to do with its size.

    Anyway, if it is true that the list of popular PR mods really isn't all that big, as you suggest, @King Fan (and I think rightly so), then perhaps my question should be re-formulated. Perhaps it is a combination of already-near-perfection + great size that makes it a desideratum less than something about its circuit topology. I will say, though, that it's a circuit that sounds great stock in a small room with a 10" speaker or one that be "expanded" not at its design core but at the level of big iron and the like (though I suppose one could fairly call this a part of the design core; I've heard folks opine that a PR that is not struggling to deliver the current is not a PR) to be made to perform at the highest level most folks need these days. That is, the circuit itself sounds good both "small" and "big," and that itself seems unusual. I'm not sure that's true of all amps. And that's what made me think that there was something about the circuit of a PR that was special in that respect.

    And for those of you who've been servicing amps for a long time, I'd be very interested to know when you first started seeing 12" speakers being put into a Princeton Reverb cab or even upping the output transformer. I'm thinking these things weren't done in, say, '64, but perhaps I'm wrong about that.
     
    Last edited: Jun 14, 2020
    King Fan likes this.
  8. schmee

    schmee Doctor of Teleocity Silver Supporter

    Posts:
    12,679
    Joined:
    Jun 2, 2003
    Location:
    northwest
    That is exactly what it is! It's very cool cloth, it has actual metal brass "thread" (fine wire) running through it. The gold looking stuff. It's strange, if you bend a tight corner on it, it just stays that way from the metal instead of bouncing back.
    The gator covering isn't bad, not great , a bit gummy. I bought it in Hollywood at this second hand place that sells all kinds of stuff from Hollywood picture props and leftover materials. I got some really cool looking heavy duty Grey Tweed stuff there too.

    This Fender Princeton amp chassis has been a mod platform for years. I bought it off Ebay someone had literally run a saw through the side to cut it out for a Bassman power tranny. It's been many things over the years. From 6L6's with Super Reverb size trannie's to stock PR.
    Now it's stock PR except a Vibrolux PT and Deluxe OT. It's dead quiet and has far more headroom than just adding a DR OT does. That PT makes a huge difference even with stock filters.
     
    Last edited: Jun 14, 2020
    robrob likes this.
  9. Wally

    Wally Telefied Ad Free Member

    Posts:
    37,276
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    If you ever need some of that type of cloth, I have some that needs to be put to use. I just tore down a Baldwin OrgaSonic last week and got some more....like I need it, right? Hey, I got another Leslie speaker unit out of it!!....very similar to the one around which I built this 14x19x27 unit that weighs in at 37 pounds! That is a two-sped Md. 120 unpowered Leslie to the left. 2FD023A0-CDC8-4A8B-8187-CAB2887DC27A.jpeg

    I may have too many Leslie units.....too much of a lot, it seems.
     
  10. Axegrinder77

    Axegrinder77 Tele-Afflicted Ad Free Member

    Posts:
    1,132
    Joined:
    Mar 21, 2019
    Location:
    Springtown
    I think it helps that the PR has such a nice thick clean base tone, so it's not generally an amp you give up on, but mod it rather.
     
    theprofessor likes this.
  11. tubegeek

    tubegeek Friend of Leo's

    Age:
    60
    Posts:
    3,879
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    @King Fan, you ignorant slut.
     
    tomkatf, robrob, hepular and 2 others like this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.