How hard is a cap job on a Fender Princeton?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by palomorado, Sep 21, 2006.

  1. palomorado

    palomorado Member

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    I have a '68 Fender Princeton Reverb that needs some blackfacing and a cap job and I was thinking of doing the work myself. I've built many a guitar pedal and done everytype of wiring in electric guitars & basses and am looking to move into amps.

    So, if anyone could give me some pointers and what i would be getting myself into that would be great!

    Gracias...
     
  2. TheAmpNerd

    TheAmpNerd Member

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    You'll do fine. They are just bigger components.
    The multisection will be a pain if you don't have a 100 watt iron.

    Some just build a pyrimid of caps above it and wire them in.

    Just watch out for the dreaded cold solder joint.

    Heck even with "experienced" people doing the work
    I'm finding way too many crappy solder joints from people
    who should know better.

    Once you learn about the Mil standards for soldering, i.e., JSTD 001 and IPC standards, it all begins to make sense.

    A lot of soldering explanations on the web talk about soldering.
    I don't recall seing one discussing the three critical temperatures:

    1. melting point
    2. wetting point
    3. bonding point
     
  3. WaltC

    WaltC Member

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    Well, here goes:
    - read and *believe* all the comments about fatal DC voltages inside the amp, proper cap discharge and protection methods and the risk you're taking
    - there are lots of opinions around about "cap jobs" including:
    -- don't fix it if it isn't broke
    -- replace everything every 10 or fifteen years
    -- only use orange drops
    -- only use mallory's
    -- etc.

    that said <G>

    The princeton is a little different from your standard blackface bassman in that the filter caps are in a "cap can" mounted vertically from the bottom of the chassis. It is possible to replace individual caps in a can but nobody I know of wants to do that or can do it effeciently or safely, so it usually means that if one of the caps is bad, you order a complete replacement can with all new caps in it from Antique Electronics Supply or a similar source.

    I'd only mess with the coupling caps (and if you don't know which they are or what I mean when I say that, you should really get tom mitchell's, or Dave Funk's, or gerald weber's or aspen pitman's book, or all of them, and read it first before you do anything else <G>) if they are leaking DC current or physically damaged or broken. Plate load resistors should be checked for drift or "crackling noises in the signal" and replaced as necessary (over 20% off of value, cracked or "noisy").

    I'd also check the resistors and caps in the tremelo circuit for drift and leakage (respectively) and replace as necessary because the tremelo circuit is where the output tubes get their bias voltage.

    If it were mine, I'd also put a three pronged power cable on it (if it hasn't already been done), eliminate the ground switch and "death cap" from you power circuit, and check all the solder joints on the eyelet board and tube sockets and re-solder as necessary.

    Then play it and enjoy...<G>
     
  4. tom grossheider

    tom grossheider Member

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    Those cap cans tend to last a long while. If it isn't humming I'd leave it alone.
     
  5. mbratch

    mbratch Member

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    I believe '68 Fender Princetons were shipped pre-blackfaced, :) so all you need to do is update the filter cap can, and other electrolytics. Non-electrolytics only as needed. Tom is correct they can last a long time. But if it does fail, it can mess up a transformer, which would not be a good thing.
     
  6. palomorado

    palomorado Member

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    Good to hear about the '68 being pre-blackfaced!

    Anyway, the amp was my father's who bought it brand new and gave up guitar a few years later when I was born. When I started playing guitar it was the amp that was given to me. The amp still has the orignal tubes.

    Recently, the reverb has been producing it's own tone regardless of the level of the master volume and I've been getting some serious humm from the amp. It seems as if a cap job is in order.

    I played a friend's "souped-up" Princeton recently and was blown away. He told me he swapped the 10 inch speaker for a 12 and then sent these instructions:

    "There is only one channel, the tremelo functions differently, the phase inverter is unique, and there happens to be a slight inherent mismatch in the phase inverter. Match that up, and while you are at it, blueprint the entire power section by matching all of the components perfectly, using the highest quality parts. Also add two 470 ohm resistors to the screen grids of the 6V6 power tubes, which was a customary practice in all of the bigger Fender amps."

    So that's what I was planning on doing for mine.
    I do need a bit of translation for some of it.
    What is the verdict on this mod here?

    Thanks for the book tips...I'll get them this weekend.



     
  7. mbratch

    mbratch Member

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    For a nice vintage amp like that, I'd fix the problems first and see if you like the sound. With it's inherent "flaws" the Princeton is a great sounding amp. After you get it sounding right, then you can make a better choice whether you want to alter the circuit to change the sound/behavior (just MHO).
     
  8. WaltC

    WaltC Member

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    On my non-reverb Princeton (tremelo only), I tried all the mods out there individually and many together, including putting in a 12" speaker in place of the (screwed in ) 10".

    When it was all said and done, the 12" speaker swap made the most difference, and I took out all the mods and returned it to stock and am just as happy (YMMV of course <g>).

    If you're careful, the speaker swap isn't that hard and would be an interesting first step.
     
  9. TheAmpNerd

    TheAmpNerd Member

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    Walt
    Did you have to cut your baffle board for the 12-inch speaker?

    Palomordo
    I'd do what mbratch says first. Fix the problems and get
    the amp going.

    THEN
    Do the speaker swap

    HOWEVER
    Do not cut the baffle board, because that and the speaker
    are original to the amp. A potential big deal to the value
    of the amp now and in the future.

    Buy a replacement 12-inch birch ply board and install it with the
    speaker of choice and see how that sounds. More then likely
    pretty good.

    There are two main schools of thought regarding basic amp maintenance


    Only replace the one or two electrolytics which die.
    OR
    When one goes its time to replace all the electrolytics at once.

    I subscibe to the latter, for peace of mind and reliability; especially
    for the working musician who relies on his amp for income. Actually
    I would rather pre-empt even that, where when one cao shows signs
    of going, all get replaced.


    AND then there is this other tech
    His theory of making Blackface Fenders sound better is to molest them.
    I'll post those specialties in another thread.

    You get the idea.

    Good luck with everything and enjoy.

     
  10. Blue Strat

    Blue Strat Member

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    They sure do. It's now almost 40 years for many of them ;)

    The question is, how much longer?
     
  11. TheAmpNerd

    TheAmpNerd Member

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    OTM,

    Not necessarily (wouldn't you know I'd speak up?).
    Consider the great thing about the Stinger missile system
    and other similar systems is that the batterys/spares are very hard to acquire, (proprietary funky configuration) and have a relatively short shelf life.

    Same with other systems' spares. That way if it gets in the wrong
    hands, or the enemy
    (OBL or Iran) of our enemy (soviet or Iraq) becomes our enemy (OBL Iran);the stuff we gave them or the stuff they bought
    from us no longer functions properly.


     
  12. brad347

    brad347 Member

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    yeah but what if some electrolytic at some soviet launching station from years ago 'fails' and launches a nuclear warhead on accident?
     
  13. WaltC

    WaltC Member

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  14. brad347

    brad347 Member

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    you won't get all the benefits of a larger speaker with that setup. Just FYI
     

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