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Part sourcing/scavenging a Princeton Reverb build

Discussion in 'Shock Brother's DIY Amps' started by choosebronze, May 14, 2018.

  1. choosebronze

    choosebronze TDPRI Member Ad Free Member

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    A few weeks ago I finished a 5F1 build from a BYOC kit (w/ instructions). What I really want is a Princeton Reverb, but I figured the 5F1 would be a good sounding, low-cost, step-by-step way to see if I could build a working amp. Turned out to be easier than I thought it would be. I’m sure the instructions and simplicity of the circuit helped. Now I’ve got the bug. I want to build more amps.

    I’m filled with all this cocky false confidence so what better time to do a Princeton?? I like woodworking, so I want to build my own cabinet. I have a non-working solid state Fender M80 head on my bench. From that I can scavenge a reverb tank and cables, and a chassis that should have more than enough room after some drilling. I have a bunch of extra tubes and a few speakers lying around. So all of that would be unnecessary if I ordered a PR kit. I can make front/back panels, and I think making my own footswitch will be sturdier than any of the kit ones.

    I’m cheap! So I’m thinking I’ll take the parts I’ve got, order the Mojotone PR small parts kit (http://www.mojotone.com/kits/BlackfaceAmpKits_x/Blackface-Princeton-Reverb-Style-Small-Parts-Kit), order the transformers + reverb driver from Classic Tone (looks like the 40-18019 PT and 40-18045 OT - maybe someone could tell me if I'm wrong on that).

    I guess the question is: Am I missing something here? It seems pretty straightforward, and like I can get all the parts I need for under a few hundred bucks. Feels too good to be true. Is there something I’m failing to take into account? Building from a layout instead of instructions will be a challenge, but I think I can do it as long as I take my time. And I’m sure I’ll be back when I get in way over my head…

    As always, a sincere thank you for sharing your knowledge.
    - Jared
     
  2. tony hunt

    tony hunt Tele-Meister

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    some thoughts:

    1. I heard a PR from a very active member on this site called Jon and it was one of best amps that I have heard. It was not stock. If I remember correctly it had an Allen output transformer and a 12" speaker. Classic Tone are fine for guitar amps, I use one in an old '59 Deluxe. But I think you want to consider/ask yourself if that standard PR type output transformer is right for you.
    2.Maybe you want to factor in your time cost into your calculation. Estimate it and x 3 = probably not enough.
    3. Reverb tanks come in different impedance ratings. You need to check the one you have against the requirements of the PR circuit.
    4. Now is the time to build off of a schematic together with a layout. If you just go by layout, then you have little chance of gaining any understanding of how the stages of the circuit work together to make an amp. Without that knowledge, you will then have an awful time trouble shooting the issues which will crop up.

    Cheers, tony
     
  3. dan40

    dan40 Friend of Leo's

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    The Princeton Reverb makes for a good follow up. It is a bit trickier because it employs the reverb circuit, bias vary tremolo and tonestack wiring. Most builders choose to mod the bias circuit with a pot to make setting the bias easier. Hoffman has a very good layout for the bias mod on his sight. The power supply wiring can be a bit tricky when following the Fender layout. It can be confusing for a beginner to follow but it is important to follow the Fender lead dress on the B+ rail and tonestack wiring. The reverb circuit adds an extra challenge to the build also but it should be fairly straightforward. Just be sure to do your homework and read all of the build threads here that you can find. They will answer alot of questions that will arise during the build. Good luck!!
     
  4. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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  5. choosebronze

    choosebronze TDPRI Member Ad Free Member

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    Thanks guys,

    Tony, I'm pretty comfortable working from a schematic. I've built probably 30-40 pedals, many from veroboard layouts I've drawn from schematic. I just need to keep a reference around for the connections to tubes/transformers. That's all new to me. I'd never thought about changing the OT. I figured I'd just build stock. People seem to be really high on the Billm TO-20, so maybe that's how I'll go. Haven't read anything bad about it.

    As for my time, the 5F1 took a weekend. I anticipate this amp will take a few months since I can't always get free time. But $1,000 on buying another amp probably causes more marital discord than a few weekends of me locked in the garage...

    Thanks for the tip on the tank. I'll check the impedance.

    I realize when all is said and done I could probably get all parts in a Weber kit for just a few bucks more, but there seems to be a consensus that the quality of the parts (capacitors in particular) isn't great. In a perfect world I could order all the individual parts myself, but I don't think I have the patience, and that's certainly not the inexpensive way to go.
     
  6. choosebronze

    choosebronze TDPRI Member Ad Free Member

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  7. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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  8. schmee

    schmee Doctor of Teleocity

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    The PR is a pretty easy build, and easier in a PR chassis than those tiny tweed chassis! There may even be chassis on Ebay cheap. Weber chassis are ok but have different spaced hole layouts. Than a standard PR. I have used the Mojo chassis and their thick faceplate before. I also have a brown custom Faceplate for the Weber chassis with a Mid control, Cut and Master volume. ($20)
    Many options, sometimes better to buy a chassis plates and then buy your own small parts.
     
  9. choosebronze

    choosebronze TDPRI Member Ad Free Member

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    dan40 mentioned Hoffman. I always forget about that site, but that might be the way to go. He's got a tone of info, photos, tips, etc. for his boards. If I get stuck it's just another resource available. And I can just remove any parts I don't need from his parts list. Prices are really reasonable too.
     
  10. aerhed

    aerhed Friend of Leo's

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    PR chassis's $50 on eBay. Weber transformers. Use the PT for the 6A14HP. Has two secondary voltage choices. The transformers save you more than the chassis cost. The Weber eyelet board set is nice and it's cheap. Resistors and caps are actually the cheapest parts you know. If you use or make a BOM list you can order packs and have spares. AES has most of them and goodies like sockets, retainers, switches. Every kit I see has parts I don't like and/or parts that cost too much.
     
  11. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    As someone else mentioned, I don't believe that reverb pan will end up working out.
     
  12. choosebronze

    choosebronze TDPRI Member Ad Free Member

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    Yea good call guys. I didn't know the tanks had different impedances. I checked and the M80 tank will not work in the PR circuit as designed. And I just got a 15% off email from tubedepot, so aerhed might be right. Time to just bite the bullet and spend a couple hours selecting all the parts I want.
     
  13. choosebronze

    choosebronze TDPRI Member Ad Free Member

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    I ended up just getting most of the parts I needed from Hoffman. So much great info on his site, and his prices really can't be beat.

    It seems like some people really like the mid pot mod, and others think it's a complete waste of time. So I was thinking of doing it, but making it switchable. Either a separate switch on the back, or a push/pull. I think I've got it - is it as easy as this, with say a 25k pot?


    Screen Shot 2018-05-26 at 12.02.08 AM.png
     
  14. Les Gear

    Les Gear TDPRI Member

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    You've got the standard 6.8k Fender scoop hard-wired on one side and 0-25k Ohms on the other. That's a great notion but the reality is that below 6.8k -- i.e. 'more scoop' -- aren't great sounds to most folks.

    I just finished a Weber 6A14HP using the Hoffman PR turret board. I put in a 15k midrange pot but hard-wired a 6.8k resistor in front of it. That way, 0 = Fender spec and more than 0 give more midrange, topping out at 21k. It works pretty well -- I sometimes like a little more midrange than spec but I'm not looking for tweed-tone on this amp.

    Good luck with your build.
     
  15. choosebronze

    choosebronze TDPRI Member Ad Free Member

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    Thanks Les. I guess I was thinking more about the option than about which tones would actually be usable. Maybe I'll try it your way. Always easy to add the switch if I ever thought it would be useful.
     
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  16. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    I did the exact same ^ recently, simple to do (and undo). I usually leave it at 0 or 1. On the few occasions I play acoustic I like being able to add more mids.
     
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