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Princeton Reverb Head Amp, 3nd guitar amp build

Discussion in 'Shock Brother's DIY Amps' started by pfarrell, Mar 1, 2021.

  1. pfarrell

    pfarrell TDPRI Member

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    This is a small chronicle of my 3rd (Can't change the post title "3nd" it is!) amp build to date—well—4th I guess—Made 2 Champs at the same time followed by the sublime 5E3 RobRob Deluxe. That amp is freaking awesome—and I figured out how to make it sound like the Champ—well, pretty close—Champ is some kind of special to be honest.

    Princeton Reverb up next—and it's turning out a bit more complex than I might have expected—it's actually quite tight—chassis is stock size I believe, but no front bevel—I don't have a proper brake that's up to my standards—found a blank steel chassis on ebay that a guy out West is making—VERY nice. It's refreshing to work with steel. There's a reason that Fender put everything in a "tray" and hung it from the top of the cabinet—WAY simpler than what this is turning out to be—it will be fine—but I've decided to label all the leads since I will have to to mount the board in a way that I can't easily spot check it later....and it will be SO easy to mix things up.

    Yesterday, before drilling holes—I realized that the amp board will have to be "hung" from the "top". Kinda plays mind tricks on you—and I considered flipping everything—which actually wouldn't have solved anything and really the only way to have done this is to have flipped the turret board layout completely. Board was already built—and that would have been way harder to sort the wiring anyway..

    I did take a second and look at the "tray" layout—but I prefer the controls at the bottom for whatever reason, visually.

    @robrob mentions someplace about upgrading the cap can to a 40/20/20/20 version? Is that worth considering?
    Was also curious about the RCAs—I'm just used to the audiofile route where everything is shielded from the chassis.
    Will there be a similar situation here with the OT and phase? Like when I built the 5E3? Can't predict which lead should go to which 6V6? Assuming yes?—noob style.
    Was likely going to put the heater wires in the chassis corner—proximity to reverb tank RCAs?? at the end of the run? Didn't think about that...

    Plan is to make a 2x10 speaker cab for this. I also have a Creamback 12" hanging around—was going to try that in the 5E3 at some point in the future. Maybe.

    Waiting on front and back panels before proceeding with the chassis—had a little fun with the nomenclature. And was liberal with my interpretations of how to hyphenate numbers.

    PF-AA1164-Build_04.jpg
    PF-AA1164-Build_02.jpg PF-AA1164-Build_03.jpg PF-AA1164-Build_05.jpg PF-AA1164-Build_06.jpg PF-AA1164-Build_07.jpg PF-AA1164-Build-FrontPanel_01.jpg PF-AA1164-Build-FrontPanel_02.jpg
     
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  2. Telefsantasia1

    Telefsantasia1 Tele-Meister

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    Very cool looking front! Nice work brother,nice....Edward
     
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  3. Gris

    Gris Tele-Meister

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    Upgrading electrolytics is def worth it. Tightens up bass which is needed in these amps. Also should consider running a wire from bass pot to addit pot (mid control - in lieu of 6800 resistor) on one of spkr jacks in back. No need to go above 25K for mid pot.
     
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  4. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Ouch! What a nightmare for troubleshooting.

    :eek::eek::eek:
     
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  5. pfarrell

    pfarrell TDPRI Member

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    Haha. It'll be fine.... Def not a "first project" though...! Makes my brain hurt a bit—glad I have the others under my belt as it were. Troubleshooting? What's that? :cool: Also very curious to see some other amp designs where the chassis/controls are on the bottom—inside layouts I mean. I don't have anything to go on other than what's in front of me—logic (or not!).... I could mount the board inside the cabinet floor, that seems even more complex and not service friendly. I could have made the current "top" the bottom and made a lid with all the parts on it—seems not great either....could employ some lead—soldered/wirenut/shrink tube connections—thinking reverb OT specifically—for later ease....etc...

    See image—mid control? @Gris

    AA1164-Mid-Control.png
     
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  6. OldPup

    OldPup Tele-Meister Ad Free Member

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    I'm confused about whether or not the chassis will be hanging from the top of the head or resting in the bottom. Will the input jacks be on the left side of the chassis either way? That's what your rendering shows, but if you're flipping the chassis and its contents, what was on the left to begin with will end up on the right, etc., right? Maybe I'm missing something.

    Either way, I am very jealous of your builds. It looks like a lot of fun and your work is excellent, especially the tolex, which seems very daunting. I put together a 5E3 kit and loved it. I am not at the point where my wife is cool with me buying another kit, so I am making do by wrenching on the old Fenders I have.
     
  7. pfarrell

    pfarrell TDPRI Member

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    Thanks!—No confusion—I just put both drawings in there because when I realized the added complexity—my original plan was to have the controls on the bottom—I took a look at them on the top since it would have been an option—and yes everything would have to flip but orientation of controls wouldn't have changed.

    I'm doing controls on bottom—mounting the amp board "right-side" up—which means you will be looking at the bottom of the board when it's installed. Hence the labeling of all the leads. And it won't visually line up with any of @robrob s beautiful wiring diagrams... But I'll figure it out...
     
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  8. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Great project. But whoa mama, I could barely figure out how to build a PR "sunny side up." This is totally messing with my head, like a Christopher Nolan movie. :)

    Is there a difference if you flip the chassis L–R vs. top-bottom? Probably not. Or, hmm, lessee. (Sorry, I know it's way too late to think about, since you've punched all your good-looking holes.) Here's my former desktop/lunchbox 5E3 *head* from Lil Dawg, seen 'upside down'. Same guts orientation as it woulda been in an original (yes, vertical) combo, *or* if it were an open-top tray amp like a PR.

    561FB189-1878-4FA3-9E26-657D2C65A25A.JPG

    So what happens on the top and more importantly on the front? Aha, insides normal, but outsides reversed. Tubes and transformers are no big deal, but the control panel...

    9153D0B9-190F-42D5-B0C7-CBE2CF717F48.JPG
     
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  9. pfarrell

    pfarrell TDPRI Member

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    That is gorgeous.

    I'm gonna proceed. It will be fine—just need to be careful and label stuff. And have a hook up plan. Less worried about the control side. Of course this assumes the board is good. :lol:


    EDIT: Maybe coming to my senses? I'm sure I could make it work... But for longevity and tech support...
    I already have the front and back panels committed to $$, and for some reason, yesterday, when I looked at mounting the chassis tray style like Fender does it seemed like it wasn't going to work—but I just mocked it up and it does...also that version (controls on top) is kinda growing on me...I have long bolts and could make straps...

    PF-AA1164-Build-FrontPanel_02.jpg
     
    Last edited: Mar 1, 2021
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  10. pfarrell

    pfarrell TDPRI Member

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    Little update...
    Chassis layout sorted, pics later. Waiting on some parts—and front panels... Made some progress on the cabinets...and a mockup. Came out a little taller (golden ratio!) than earlier projections—has just enough space and oval back cut out (not shown) to house the pedal. (Grill piece will be aluminum)

    PF-AA1164-Build_08.jpg

    PF-AA1164-Build_09.jpg
     
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  11. RollingBender

    RollingBender Tele-Afflicted

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    I did a similar gille on a build but I have it in the back.
    2ECAF974-F8DF-49D3-AE8D-EAFD464F834F.jpeg
    How will you be making yours?
     
  12. pfarrell

    pfarrell TDPRI Member

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    Okay. That's excellent—I like the chamfer on the openings, nice detail—thanks for showing it. I was going for something classic-ish and not overly "grill-y" but with a bit of style. Might change it up at a later date. What's the amp? And what's the front look like?
    I'm going to do an open back speaker cabinet—I can always close it up—putting the jack in a similar spot as yours—open back suits our space—and seems like "reverb everywhere" would be a good thing. Some pics of other places I've used that grill design—and a different one I considered (not see-through enough for this I think) that I made last year for a phono preamp. (Sorry, not guitar related—still amps though!). Really could do anything—which is more challenging than it reads.

    Sissy-Cases_03.jpg UFSP-Build-Closed_01.jpg UFSP-StarryNight-01.png
     
  13. pfarrell

    pfarrell TDPRI Member

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    Guys—this midrange control "hack"—replacing 6K8 mid resistor with a pot... does the pot need to be a log pot? I have a 25K linear sitting here.

    Was also going to put it on the back of the amp in the corner V1 area, kinda the only place there's space...


     
  14. printer2

    printer2 Poster Extraordinaire

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    Linear is perfect.
     
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  15. pfarrell

    pfarrell TDPRI Member

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    I just realized that on chassis #2 orientation redo—I inadvertently aligned the tube sockets differently from how they appear in other builds.. Meaning the diagonal of the mounting holes placing the pins in a different rotational orientation. I recall reading someplace about this but can't find it now.... Would this be more about lead dressing potential noise issues, or is there some specific practical reason, maybe my question isn't clear? I have no issues adding holes and changing things before this gets any further. I was going to run heater wires in the corner of chassis—but to me, they will be more away from everything else if I run them high, up the socket centers, like I have in other builds.... 5E3 is REALLY quiet, so that's the extent of my understanding. Also my output jacks ended up a little farther left than I might have thought was wise...hopefully no issues there either... Oh, and seeing as how there isn't a heater CT noted on @robrob 's diagram, which I'm working off of—and a huge warning on the Mercury Mag transfo about not using it if it's not on your layout—it's deactivated... (Mid pot in lower right dialed in to 6K8, bias pot dialed in to 22K)...

    PF-AA1164-Build_10.jpg
     
  16. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    I useta know something about socket rotation, but I’ll defer to somebody smart. On your CT, are you creating an artificial heater CT? All MM is saying with that scary yet cryptic warning is if you have an artificial CT in an existing amp, don’t use the real CT... it’s just the usual 'one or the other but not both' rule.
     
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  17. pfarrell

    pfarrell TDPRI Member

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    Ah, so I should connect it? Tie it to preamp ground? Don't see a reason to create one if I have the lead available from the transfo....?
     
  18. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Lets just make sure. . Are you following Rob's layout? Including the artificial CT he shows here? If so, no real CT. If no, yes real CT, but ground it with the power amp, not the preamp.

    E34EA19A-EB15-47A1-98F1-FBA343076B6C.jpeg
     
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  19. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Ah, Cool Hand Luke time. “What we have here is a failure to communicate.” If I see straight, you already have an artificial CT.

    4988A07E-C716-4926-BA34-396179B61D2A.jpeg
     
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  20. pfarrell

    pfarrell TDPRI Member

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    Yea! That’s a bit more clear... So is there a “better/best” way to do it? (Quieter/quietest?) Meaning It's easy to undo @robrob's and connect the CT since my transfo has one...Presumably his drawing is about modding an existing amp (or what's commonly available for transformers for PR?) as opposed to a preferred methodology?

    I love that line btw... from Cool Hand Luke. (no failure to communicate IMO—just my own ignorance on display...)
     
    Last edited: Mar 10, 2021
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