Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Princeton Reverb Build

Discussion in 'Shock Brother's DIY Amps' started by Phrygian77, Aug 26, 2017.

  1. Phrygian77

    Phrygian77 Tele-Holic

    639
    Apr 30, 2016
    Crawfordville, FL
    The time has come to turn my Princeton Reverb chassis and cabinet into a proper Princeton Reverb. I'm probably going to sell it when I'm done to make up for what I dumped into my Bassman build. Hopefully, I can at least get the cost in parts out of it.

    I'm going to make the eyelet and insulators boards out of leftover 1/16" Garolite XX that I have. I'm still working on the layout for it. I've moved some eyelets around and added eyelets to make mounting some of the components a little easier.

    PR Layout Draft 1.jpg

    I wanted the caps in tremolo to have a better temperature coefficient than the monolithic Z5U disks, so I decided that I'm going to try some X7R MLCCs. I don't want to try to stuff film caps in there. Murata seems to be the only company that makes MLCCs with a decent lead length, so that's what I'm going to go with. They're cheap too.

    Coupling caps will probably be Mojo Dijon. The smaller values will be CDE mica. Most of the resistors will be Xircon 1W carbon film because I still have a big stash of common values. PS resistors will be Vishay PR03 and PR02 metal film.
     

    Attached Files:


  2. sds1

    sds1 Tele-Meister

    Age:
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    Orlando, FL, USA
    Subscribed!
     
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  3. Phrygian77

    Phrygian77 Tele-Holic

    639
    Apr 30, 2016
    Crawfordville, FL
    These things are tiny!

    1504042613528.jpg
     

  4. Phrygian77

    Phrygian77 Tele-Holic

    639
    Apr 30, 2016
    Crawfordville, FL
    I got a lot of parts in this week. When I did an inventory of my electronic components, I forgot I had some CDE type 150 that I could use for the tone stack. I ended up ordering some 716Ps for the rest of the coupling caps, and a 0.1uf Xicon MPP for the tremolo.

    Here's the updated layout...

    PR Layout Draft 2.jpg

    PDF version is also attached.

    Now, I need measure the locations of the mounting screw holes in the chassis so that I can add them to the board layout.
     
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  5. Phrygian77

    Phrygian77 Tele-Holic

    639
    Apr 30, 2016
    Crawfordville, FL
    Forgot the PDF
     

    Attached Files:


  6. Phrygian77

    Phrygian77 Tele-Holic

    639
    Apr 30, 2016
    Crawfordville, FL
    Pulled the chassis yesterday, and removed the Champ board and the single ended OT. I forgot that for some reason I went crazy with the zip ties on that build.

    I was hoping not to touch any of the 120 VAC wiring, but I think I'm going to remove the fuse holder to make soldering one of the octal sockets easier.

    I also forgot that I had cut the filament leads from the PT a little short on that build. I don't like the way it looks, and it could potentially break in the long run. I think I'm going cut the leads even shorter and add some wire there to be safe. Even though that won't really look right either, at least I'll feel better about it.

    I got a ClassicTone DR type output transformer to go in this build. I was a bit concerned about the mounting screw on the B+ side of the board interfering with the OT, but since I'm going to be using thread forming screws to mount the board, it doesn't look like that will be a problem. I will need to rotate the speaker though to keep the OT from hitting the speaker frame (the PR cabinet has a 12" speaker baffle).
     

  7. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Phryg, I admire your planning ability and grasp of options. Thanks for details -- I'm learning.
     
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  8. Phrygian77

    Phrygian77 Tele-Holic

    639
    Apr 30, 2016
    Crawfordville, FL
    Thanks, man. I plan to avoid disaster, but even with the best planning, mistakes are inevitable. I'm still pretty inspired by my Bassman build, which for me was near perfection. It's going to be really hard to top that.
     
    Last edited: Sep 16, 2017
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  9. Phrygian77

    Phrygian77 Tele-Holic

    639
    Apr 30, 2016
    Crawfordville, FL
    Yesterday I discovered that the mounting screw holes in the chassis are too big for the 8-32 thread forming screws. I don't understand why it's different from the Bassman chassis that I got from the same maker. Once again, I think the guy is just directly copying the Mojotone chassis, inconsistencies and errors included.
     

  10. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    I feel your pain -- I'm dealing with the opposite problem: where I bought a mostly undrilled chassis and have to drill all the right size holes for different mounting bolts.

    What holes are these? You will have thought of this, but I often like to use Keps nuts on straight 8/32 bolts instead of self-tapping once I get up to 8s.
     

  11. Phrygian77

    Phrygian77 Tele-Holic

    639
    Apr 30, 2016
    Crawfordville, FL
    The holes that I was referring to are the holes punched for the main eyelet board and the bias board. They're a little over 11/64, so I'm not sure if a 10-32 thread forming screw will work. On my Blackface Bassman chassis, the cap pan, cap board, and bias/rectifier board holes were all just under 9/64. There were no holes for the main eyelet board on that chassis, which kind of makes sense because the screw layout may vary depending on the version you're building.

    If I rotate the output transformer (I'll need to check the speaker frame clearance again), then I can use a regular 8-32 machine screw and a Keps nut. I don't think the transformer will clear an 8-32 Keps nut, so I'll have to put the screw through from the outside. That also means I'll have to mount the board before the OT.

    Trying to use machine screws with nuts on the Bassman would have been a real pain. The center mounting screw for the main eyelet board goes through the chassis right where the cap board is on the outside, and the screw on the preamp side of the board just barely clears the cap pan.
     
    Last edited: Sep 19, 2017

  12. FADECBNA

    FADECBNA TDPRI Member

    Age:
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    Nashville TN

  13. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Heh, I knew you'd thought all round this issue. Stuff like a doghouse on the bottom of the chassis is huge, and a real argument for self-tapping screws. For trannies, maybe you're using something different than I have in mine, but first I check my exact location (MuchXS once pointed out to me that he liked the Mojo PR chassis, but needed to "move the OT 1 inch towards the preamp side so the circuit board mounting screw doesn't foul the transformer").

    More generally, if your OT is like mine, and if you can choose where to drill the board, I do what Doug Hoffman suggests after a long discussion of avoiding bottom side obstacles:

    Mount the board into the chassis using #8 Screws, Keps Nuts and Standoffs.
    If you are also installing transformers, you may want to install them first if any screw heads are going to be under the board.
    It will be difficult to install a transformer later if the screw heads are under the board.
    I suggest having the transformer screw heads under the board and the nuts on the outside of the chassis.
    Again, I know you've thought this through, but I offer that just in case it helps.


     
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  14. Phrygian77

    Phrygian77 Tele-Holic

    639
    Apr 30, 2016
    Crawfordville, FL
    There's no way I could move the output transformer a whole inch with the 12" speaker baffle. I rotated the speaker last night, but I still need to check the clearance. All I really need to do, to be able to use a 6-32 Keps nut, is slide the OT by about 1/16 to 3/32 over.

    Here's the mounting screw layout/dimensions for the Zachmdhunter PR chassis.

    ZH PR Chassis Mounting Holes.jpg
     

  15. Phrygian77

    Phrygian77 Tele-Holic

    639
    Apr 30, 2016
    Crawfordville, FL
    Well, with the speaker frame rotated, I could move the OT a whole inch or more if I really wanted to...

    1506481249546.jpg
     
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  16. LudwigvonBirk

    LudwigvonBirk Tele-Meister

    Age:
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    Aug 26, 2017
    Madison
    Having been exactly where you are now... you can move the OT (one, or both mounting screws) to a nearby spot where the OT is not parallel to the PT and it won't cause any weirdo hum or new noise thing. If you were wondering.

    [not true everywhere else esp as transformers go up, but predictably ok here]
     
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  17. LudwigvonBirk

    LudwigvonBirk Tele-Meister

    Age:
    115
    139
    Aug 26, 2017
    Madison
    Seconded! If you do the opposite it'll surely bite you (or the next person that has to go in there)
     

  18. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Excellent info. I checked. I moved mine less than an inch. Here it is with the board just lying in the chassis to check L-R spacing.

    IMG_3381.JPG

    The issue in the Mojo kit is the mounting bolt in the vertical center of the board. You could move that, but as seen in the pic the OT holes were also too close together, so the OT move was a double fix.
     

  19. LudwigvonBirk

    LudwigvonBirk Tele-Meister

    Age:
    115
    139
    Aug 26, 2017
    Madison
    Nice.

    "There's a reason" why things are in the spot they are in most cases with a 50+ year-old design like this. I was hesitant to move the OT at all, at first.

    But with the amp on and signal passing through it, I (with a rubber glove on) moved the un-mounted OT around a bit and noticed no new/odd hum or noise in the new spot I picked, which ended up quite close to where yours is. I'm pretty sure there are transformer mounting spots that would be "bad" (like over the input jacks).
    ...
    I realized fairly recently that I really don't like any screws or wires underneath the board- getting under there to fix something or look for problems is a total hassle and mucks up a careful wire-dress at the very least. Do you run all the wires over the top of the board, King Fan?
     
    Last edited: Sep 27, 2017

  20. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    I like your empirical approach. It was a lucky break I got that advice from MuchXS or I'd have been hesitant. Of course the stock Champ iron in a PR isn't cranking huge EMFs.

    Good question about the back-o-board wiring. Much actually suggested he preferred your method, keep everything where you can see it, and noted Fender tended to go that way in later years, but allowing for vintage-osity I was going for, I just triple checked everything a few different times.

    This is turning into a thread hijack. Sorry, Phryg!
     

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