Mojotone Princeton Reverb Kit

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by dbrow, Apr 20, 2015.

  1. dbrow

    dbrow Member

    Messages:
    23
    Joined:
    Oct 19, 2014
    Hopefully this is the correct forum for this topic.

    I'm interested in building a Princeton Reverb clone. I have looked over all the possible kits out there ( Mojotone, Weber, Marsh etc.). I have decided to go with the Mojotone kit. Before I pull the trigger I wanted to get a good idea of how good this kit sounds, however, there aren't many videos around which showcase this kit.

    For those forum member who have built this kit, is the final product very close in sound to a vintage Princeton? Is there any speaker you found to be more fitting than the C10Q that comes with the kit? Lastly, on what volume settings (with single coils and humbuckers) did the amp start to break-up at? Was the tremolo weak?

    Thanks,
     
  2. cap47

    cap47 Member

    Messages:
    2,243
    Joined:
    Sep 16, 2009
    Location:
    Bushnell, FL
    Can't vouch for the PR but, I have the 5E3 and it is excellent quality!
     
  3. swiveltung

    swiveltung Member

    Messages:
    14,566
    Joined:
    Feb 5, 2011
    Location:
    PNW
    I used one of their kits for the PR ( I didn't do the exact replica though) I think their kits are great. better components than some others.DO NOT use the C10Q though. Crappy speaker. a PR will break up pretty readily... depending on how you are pushing it. I doubt their kit is different enough to be any different than most PR's .They are simple and a great amp to build and learn.
    One thing to consider is.. can you substitute a fat stack power transformer? That would give you the option of going to 6L6GC's later with an Output transformer change....
    If Mojo sticks with the Tube Bias tremolo that PR's have it will have great tremolo.... I cant remember,, but think they do.
    Later:I just checked their schem and it's tube bias tremolo.
    I would order it without the Jensen and without the JJ preamp tubes.
     
  4. mark norwine

    mark norwine Member

    Messages:
    16,144
    Joined:
    Jul 25, 2005
    Location:
    NJ...GSP135
    great kits, high-quality parts. Mojo is awesome.

    That said, building an amp kit isn't legos....you need to have at least a basic notion of what you're doing.
     
  5. dbrow

    dbrow Member

    Messages:
    23
    Joined:
    Oct 19, 2014
    Which speaker would you recommend its place? Why no JJ's for the preamp?

    I decided to do this because I ordered 2 Fudge Brownie Princeton Reissues and got 2 defective amps, I got sick of getting ****** quality. The fudge brownie has a P10Q speaker in it which I loved, however, I do not know what a true vintage PR sounds like. I only know what a reissue sounds like. So my other option for the speaker was a Jensen P10Q.
     
  6. dbrow

    dbrow Member

    Messages:
    23
    Joined:
    Oct 19, 2014
    I will be building the amp with the supervision of a very experienced amp tech from my city of residence.
     
  7. drbob1

    drbob1 Silver Supporting Member

    Messages:
    21,971
    Joined:
    Aug 9, 2004
    The Italian Jensens don't sound a lot like a vintage one. Vintage ones are pretty played clean, with sparkling highs. Pushed they get a little mean, almost with a bark like a Celestion (especially the P10Qs). They aren't super tolerant of high output, so for a Princeton a P10Q or P10P pulled from an organ would be just the ticket. Or better, build it in a 112 box and use a vintage P12Q!
     
  8. mark norwine

    mark norwine Member

    Messages:
    16,144
    Joined:
    Jul 25, 2005
    Location:
    NJ...GSP135
    Then you'll have an awesome adventure, resulting in a great amp!

    Enjoy
     
  9. dbrow

    dbrow Member

    Messages:
    23
    Joined:
    Oct 19, 2014
    When I mentioned the P10Q, I meant the reissue.
     
  10. xtian

    xtian Member

    Messages:
    1,674
    Joined:
    Dec 15, 2010
    Location:
    NorCal
    I used a Mojo PR chassis to build my own. Great, steel chassis, very nice. I used Hoffman's layout. Built my own solid pine cabinet with 12" Jensen Jet Falcon. BTW, I think JJ 12AX7s are fine tubes. Photos here:

    http://amps.monkeymatic.com/2014-monkeymatic-shasta/
     
  11. fenderpro

    fenderpro Member

    Messages:
    346
    Joined:
    Jan 6, 2006
    Location:
    bay area CA
    xtian, that is a great job. if it sounds anywhere near as good as it looks, it must be a killer.
     
  12. dbrow

    dbrow Member

    Messages:
    23
    Joined:
    Oct 19, 2014
    That is what I call amp porn!
     
  13. xtian

    xtian Member

    Messages:
    1,674
    Joined:
    Dec 15, 2010
    Location:
    NorCal
    Thanks guys. The only issue I had was with the bias-vary tremolo. In order for the tremolo to go deep enough for my taste, I had to adjust the fixed bias cooler than I might normally, maybe 55-60%, giving me about 10 watts clean output. I also modded the tremolo for longer period of oscillation. It's a great home/stage/recording amp.
     
  14. Don A

    Don A Silver Supporting Member

    Messages:
    4,796
    Joined:
    Nov 3, 2004
    Location:
    Massachusetts
    Mine sounds very similar to the '68 that I used to own.

    I have a C10Q reissue that I've used in other amps for years and I like it a lot. It was really just a matter of breaking it in.

    My amp breaks up at fairly high volumes with a Strat, lower with a Tele, even lower with humbuckers. I don't know the settings.

    The tremolo was weak when I had the bias set hot. At normal bias settings it sound good.

    I added an Allen amps style Mids/Raw pot to the back of mine. It's in series with the stock 6.9k mids resistor so it's stock set at 0. It adds a lot of punch and gain to the amp.
     
  15. swiveltung

    swiveltung Member

    Messages:
    14,566
    Joined:
    Feb 5, 2011
    Location:
    PNW
    There are some JJ pre tubes out there that are just nasty mushy sounding. I'm not a tube snob, in fact don't use vintage pre's anymore, but I tried those and they made the amp sound terrible. Recent post on the Weber board by someone else about this also.

    Trying to recommend a speaker is tough, but I would probably use a Weber 10F150 or 150T. (see the recent thread on "don't give up on your 10" on TGP- not mine)
    (I have a nice 10F150T I might be selling, so contact me when you get that far... haven't decided yet.)
    The Jensen C10Q is a bright speaker with little character and not much low end. A few people like them, and I have used them in combo with other types, but alone they lack a lot.
    There's one resistor you can change to make the tremolo deeper if it ends up not enough for you....
     
  16. dbrow

    dbrow Member

    Messages:
    23
    Joined:
    Oct 19, 2014
    How early did the humbucker breakup? And what is defined as a normal bias setting?

    Sounds like I'll end up going with the stock C10Q then change out if needed.
     
  17. dbrow

    dbrow Member

    Messages:
    23
    Joined:
    Oct 19, 2014
    You're right the speaker may not be my cup of tea. However, the amp sounds good with the exception of a ton of low end. If I crank the treble and bass to 8-10 each the amp sounds sweet. If I dont do that the low end dominates way too much. I'll have to look and see what the circuit differences are between the Mojotone kit and the original circuit to get a better understanding.

    I biased the amp pretty hot and yes the tremolo suffered, I ended up just completely removing that 1M resistor. Will post pictures soon.
     
  18. Don A

    Don A Silver Supporting Member

    Messages:
    4,796
    Joined:
    Nov 3, 2004
    Location:
    Massachusetts
    I built mine like a stock PR (I believe the Mojo schematic includes the Stokes mod). It's a warm sounding amp. Like you, I like it best with the treble and bass cranked. I was surprised what cranking the bass did to the sound- a lot fuller and richer but not really bassier.
     
  19. mscaggs

    mscaggs Member

    Messages:
    624
    Joined:
    Jun 16, 2008
    Location:
    Nashville, TN
    You might want to swing by Hoffman Amplifiers and get some better tube sockets. Doug is selling Beldon sockets now which IMHO are far better than anything Mojo sells currently. He also has nice reverb tanks...

    My 2 Cents
     
  20. tresspassor

    tresspassor Member

    Messages:
    926
    Joined:
    Mar 2, 2010
    Location:
    Austin, TX
    There's a few circuit mods you can try in order to tame the bass response. Mine was really bass heavy with a 12" speaker.
    * Lowering the coupling cap values feeding the power tubes. I lowered mine from .1 uF to .047 uF
    * Increasing the value of the tonestack slope resistor. I raised mine from 100K to 130K.
    * Lower the cap value feeding the bass potentiometer.
     
    mscaggs likes this.

Share This Page