Princeton Reverb - Trying to Identify Date of Manufacture

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Sailindawg, Sep 10, 2019.

  1. Sailindawg

    Sailindawg Member

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    I have a Princeton Reverb that I bought years ago for $150. A previous owner seemed to mod it by removing the tremelo pot. I've read that by bypassing the tremelo circuit one could add more gain. The tube for trem circuit is still there. In it's current state, the far right trem circuit knob seems to function as a master volume of sorts. When used in tandem with the main volume knob, there's a lot of distortion created.

    I guess I have several questions, firstly, I'd like to try to date the amp.

    Secondly, I would also like to get an opinion, if possible, how stock this amp is.

    The chassis is stamped A23136. On one website, that puts the amp around 1969. Looking at amps for sale on eBay, I came across a 1973 that cosmetically looked similar but with a higher chassis number.

    I've included a bunch of pictures. That was the best way to share pictures.

    photo1
    photo 2
    photo 3
    photo 4
    photo 5
    photo 6

    I have included pictures of the output transformers, chassis stamp and a gut shot.

    photo 1 and photo 5 are gut shots
    photo 6 is the amp
    photo 2 and photo 3 are tranformers
    photo 4 is the chassis
     
    Last edited: Sep 10, 2019
  2. Baxtercat

    Baxtercat Member

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    Google 'dating fender amps' for the chart.
     
  3. Sailindawg

    Sailindawg Member

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    I have linked the website that I used for chassis dating in my original post. The website is here.

    Apologies if the first post is tedious. It was a work in progress for a bit.
     
    Last edited: Sep 10, 2019
  4. HotBluePlates

    HotBluePlates Member

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    1973.

    The transformers have 1973 date codes (the ambiguity of "3" being the last digit of the year is put to bed by the part numbers, which didn't use that format until the late-60's). The bias filter cap appears to be date coded the 45th week of 1972 (the year numbers are just barely visible).

    Everything looks stock, except the blue-bodied resistors, the goofy wiring from the trem footswitch jack to those resistors, and whatever that is mounted in the Speed pot hole. There also appear to be two caps mounted on the Volume & Treble pots that are probably non-stock.

    The plastic-coated wire, white Mallory caps, and blue blobs would all be typical of an early-70's Fender amp.

    That info applies to Deluxe/Deluxe Reverb and larger Fender amps, which use a different way to control amp volume with the trem circuit. It does not apply to the Princeton/Princeton Reverb, Vibro Champ or Bronco amps.

    It looks to me like the modification probably uses the trem tube as an extra gain stage, and adds a master volume as you noted. IMO, this is straight stupid in a Fender amp circuit without adjusting the voicing of the existing gain stages, which will have too much bass for really great preamp distortion sounds.

    One can never go by serial # alone. Gotta look at the totality of the available evidence.

    This is especially true with vintage British amps, where lots of lash-ups & forgeries exist. And in Fender amps, the issue becomes the fact that serial numbers weren't sequentially stamped; chasses were ordered/stamped in batches. It's possible for a single chassis or transformer or speaker to have sat around a long time before being used, especially when there's no incentive for first-in/first-out.

    I'd bet any original pots still in the amp also show 1972/1973 date codes.
     
  5. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    It is moot to check the value of like-aged amps when yours is "modded". Please consider taking it to someone who can properly service it and return it to stock configuration.
     
  6. Sailindawg

    Sailindawg Member

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    @HotBluePlates

    Many thanks for the analysis! Dating amps is interesting. I've had the amp probably 20 years now, but it's just been sitting. I've been trying to identify amp techs in my area to give it a good look over, but I want to learn more about the amp in general.

    Regarding the dark blue capacitors(?), are those anything special, like Marshall mustard caps? Or they are just what was on hand at the time of manufacture?
     
  7. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    There is no special mojo, good or bad, regarding those (I think they are paktrons?)
     
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  8. Sailindawg

    Sailindawg Member

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    I have no idea what make those blue capacitors are.. I was surprised to hear that most of the amp is still fairly stock. HotBluePlate's analysis was interesting.

    Based upon what I'm hearing with the amp, a complete circuit test, re-cap, speaker replacement and repair to the tremelo circuit is in order to return the amp to a stock configuration. Probably a new set of tubes couldn't hurt. I've already replaced the rectifier tube. The amp has had some good hard miles put on it. I'm currently looking for a good tech in my area.
     
  9. Sailindawg

    Sailindawg Member

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    Not quite sure what your intention is. My only reasoning for looking at other similarly aged Princeton's on eBay was in hopes of identifying my amp's general age through posted photos.

    I happened across some good chassis photos, transformer pictures and amp pictures that I initially understood placed my amp in the ballpark of a 69-73. I also cross referenced the photos of the amps for sale with the website that I found that had chassis numbers and transformer numbers.

    I was curious, out of general interest, not mining for gold. If I want a return on investment, I'll play the stock market and manage a portfolio.

    I'm also interested in determining what a reasonable repair of the amp would be to bring it back to a stock configuration. That's my motivation here. To bring back the amp's playability, but not overspend on doing so.
     
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  10. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    From what I can see on yours, it will take 5 25uF/25V caps, a new bias filter cap, replacement pot+knob for the trem, some resistors, a bias trimpot (if you want adjustable bias) and a new can cap. The can cap is a bit pricey at about $45 or so from CED. And there will be a bit of work de-modding. But parts-wise it is not terrifically expensive. I've got a PR on the bench right now that is getting all the above, plus (unfortunately) a new power transformer. Yours should clean up well, good luck with it!
     
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  11. Sailindawg

    Sailindawg Member

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    @Jeff Gehring

    Many thanks. I wish I knew what the hell I was doing and had soldering skills. My amp would be a good project.

    What would be the benefit of an adjustable bias? I get the adjustable bias for a Marshall amp, but for a Princeton, how much tone change can be had biasing hot or cold?
     
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  12. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    It's not so much a tone thing as a make-sure-the-tube-doesn't-auto-destruct kind of a thing. Especially with amps that, due to their higher voltage plate supplies, may tend to run 6V6s on the ragged edge of their maximum allowable plate dissipation specs. It's nice to be able to stick in a new matched pair and dial them for optimum idle conduction, rather than having to play whack-a-mole trying to find a pair of 6V6s that happen to idle properly at the (non-adjustable) bias voltage of the stock amp.
     
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  13. HotBluePlates

    HotBluePlates Member

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    What @Jeff Gehring said. That's just what Fender used at that time.

    Why would the speaker need replacing?

    I would remove the circuit modifications, clean jacks, sockets, pots, replace power supply and bias capacitors, then re-evaluate. And of course, consider the adjustable bias alteration mentioned:
    100% agree. I have an adjustable bias modification in my 1962 Deluxe for exactly this reason.
     
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  14. Sailindawg

    Sailindawg Member

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    Fair question regarding the speaker. I will do the electronics first, play the amp a bit, experiment with some different speakers I have. See what I like. I guess I like to experiment.

    I'm liking the adjustable bias idea. Great suggestion!
     
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