Yard Sale 1968 Silverface Princeton Reverb

Discussion in 'Amp Tech Center' started by bkdaaa, Feb 21, 2016.

  1. milocj

    milocj Friend of Leo's Ad Free Member

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    Your amp is very similar to mine as all the transformers and those blue caps still date from the blackface era, except possibly the PT which is close to the beginning of the drip-edge. It would have been possible to swap the cover, but I believe that BF transformers had plastic wires and cloth board wires, then that reversed for the SF era. Yours is transitional with the old caps and transformers and plastic coated wiring, but the transformers would have still probably been plastic covered wire.

    To me, the wire colors of the center taps look a little strange so it is possible that somebody replaced the PT. Mine are dated a bit earlier and the pics are on a different PC. The only printing I recall seeing on the inside of transformers that old is CSA so I can't say for sure whether that's original or another part number from a replacement.

    Either way that's a huge score.
     
  2. BobbyZ

    BobbyZ Doctor of Teleocity

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    PT looks like an original to me. Just going by the groove in the laminations and lack of the copper band.
     
  3. BobbyZ

    BobbyZ Doctor of Teleocity

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    You don't need to unsolder the transformers. This amp had been un played for how long? It still has many original electrolytics.
    No matter how that amp has been handled for the last 50 years the electrolytics should be replaced. But sitting unplayed even more of a more so.

    I'd power it up with a light bulb limiter just long enough to see if the power transformer works and it makes noise.
    Then replace all the electrolytics including the cap can, install a grounded cord and non invasive bias pot.
    Probably that'll do the trick unless a transformer was shot in the first go round.

    All in all that amp looks great.
     
  4. muchxs

    muchxs Doctor of Teleocity

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    Just when it would be nice to rest up and get over my bronchial pneumonia... :rolleyes:

    I'd like to stop coughing before July 4th or so... :rolleyes:


    Why oh why doesn't the little light bulb go off over someone's head? OP, you're about $700 in the black. Why not have that thing properly serviced instead of arbitrarily messing with it? :rolleyes:

    For starters those 5881 tubes have no business in there. They draw about twice as much current as your PT is able to provide. Further, the bias isn't adjustable. The amp is biased for 6V6 tubes, probably improperly biased for 6V6 tubes as-is. When you fire it up no trem will be symptomatic of incorrect bias while a red hot power transformer will be symptomatic of impending doom.

    Transformers appear stock and correct for '67- '68.

    Attempt the conversion if you have the correct cable and the correct strain relief. Do not enlarge the hole! It's not necessary.

    This seems to be International Princeton Reverb Mess With It Until It Smokes Month. :rolleyes:

    Don't do it.

    Unless you have enough experience to get in and out of there without burning every wire in sight you're risking de- valuing a relatively expensive amp. Besides, measuring unloaded voltage tells you nothing. I can tell you what you need to know just by lookin' at it. You don't have enough juice to run 5881 tubes. An adjustable bias modification, a full cap job and a swap to the correct 6V6 tubes would all be value- added if performed by a competent tech.
     
  5. bkdaaa

    bkdaaa TDPRI Member

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    Thanks for all the input and guidance! I have decided to send it off to a vintage amp specialist in Northern Cali to have her done up right. I'll practice and learn on something else. I'll post more when I get her back. Thanks again!
     
  6. jazzguitar

    jazzguitar Tele-Afflicted

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    Don't throw away those tubes!
    (As long as they test good)

    Except for V1 (a Yugoslav Ei 12AX7 which was made on the former Telefunken equipment), you have good, US or Canadian made tubes there.
    V2 is really a 12AT7WA (military grade) long-life tube probably by Sylvania/USA,
    V3 is a General Electric 12AX7 someone put a "?" on maybe?
    V4 is a Sylvania USA 12AX7
    The power tubes are Canadian 5881 and
    the rectifier is an early 1950's 5V4G by Sylvania or RCA.

    They may still be good and the next best thing to NOS. But the amp should run 6V6s of course, while the 5V4 could be used in that amp (depends on what the voltages are).
     
  7. BobbyZ

    BobbyZ Doctor of Teleocity

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    If you're going to send it out for repairs send it to Muchxs.
    He's the guy they get sent to after other guys screw them up.
     
  8. bparnell57

    bparnell57 Poster Extraordinaire

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    Absolutely! +1000

    His work is phenomenal, and if you get the Morph mod done, you'll have a keeper for life.
     
  9. buckwalder

    buckwalder Tele-Meister

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    Your amp is a 67- early 68 by the grill cloth. Your amp has the double green thread grill cloth that on the earliest silverface amps.
     
  10. bkdaaa

    bkdaaa TDPRI Member

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    Mr Muchxs I would be interested in discussing this with you but I cannot pm you your inbox is full. Thanks!
     
  11. BobbyZ

    BobbyZ Doctor of Teleocity

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    His inbox is almost always full.
     
  12. bkdaaa

    bkdaaa TDPRI Member

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    Hopefully he comes back to scold me some more and pm's me! lol I am glad I came here to get some info on her, I was gonna figure it out on my own. I am capable, but it seems I found something that deserves to be done correctly once! I dont gig, just mess around at home and with friends. I am going to be a grandpa next month and am hoping my grandson gets into guitars as I have an old gibson I rescued from a woodpile and this amp now. They should be a cool thing to pass down to him later.
     
  13. Mhat

    Mhat Tele-Meister

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    Yeah, I agree on the transformer being original. I commented before I saw the transformer stamp codes. Super score.
     
  14. bkdaaa

    bkdaaa TDPRI Member

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    I traced out the schematic and all looked well no suprises. The great news is the speaker works! I plugged it into a little 1 watt tube amp I built a few years ago and ended up jamming on it awhile. Sounded nice. So if any repairs are needed do I request all replaced parts and keep them? Only planned mods I'm going to have done are 3 wire power cord and adjustable bias (and correct OP tubet of course!). Then I'm gonna make lots of sweet noise and decide what's next if anything. Probably a replacement 12" baffle and speaker is my initial thought.
     
  15. DakotaRed

    DakotaRed Tele-Meister

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    Why do you guys keep mentioning the value of that amp as $700?

    You might get a used REISSUE '68 Princeton Reverb for $700 but a vintage unit costs about twice that.

    I'd be thrilled to find a vintage PR for $700, but $75? Dang...
     
  16. muchxs

    muchxs Doctor of Teleocity

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    At the moment it's a yard sale amp that probably needs attention. Sure, the "untouched solder joints and all original parts" crowd likes to buy 'em cheap and sell 'em at "Grab all you can get" prices. Realistically an amp that needs service is worth a realistic price.

    The market is actually upside- down. Properly serviced amps are often worth less than something that has "untouched solder joints and all original parts" even though a properly serviced amp is reliable and functionally superior. It often sounds a whole lot better than a worn out old amp, too.

    Hassle is some of the same "Grab all you can get" guys apply a similar philosophy to service. The complete philosophy is "Do as little as possible, grab all you can get." That's dis- service instead of service.

    Believe me, I understand. I prefer "untouched solder joints and all original parts" over an amp that has been buggered by a "tech" who learned everything they know by readuing "hip tube amp books". :rolleyes:
     
  17. muchxs

    muchxs Doctor of Teleocity

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    You may also want to consider

    "Murphy's Law of Expensive Gear"

    which reads as follows:

    Princeton Reverbs may actually be $3000 amps, that is right up until the moment you buy one for $3000.

    You'd feel real silly if you paid three grand and then couldn't get your money back out, wouldn't you? It would ultimately suck if everyone else was gettin' Big Dough, everyone except you. :rolleyes:
     
  18. BobbyZ

    BobbyZ Doctor of Teleocity

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    I've seen plenty messed up by electronics engineers. :rolleyes:
     
  19. muchxs

    muchxs Doctor of Teleocity

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    At least they're not just wingin' it... :D
     
  20. bkdaaa

    bkdaaa TDPRI Member

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    LOL I am actually an RF Engineer. I do have a bound copy of RDH4 is that hip? :p j/k

    But seriously I am going to have this one professionally done as that is the right thing to do. I want this to become a family heirloom of killer tone.
     
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