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  1. #1

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    Hey There,

    My beloved 68 PR has been in semi retirement for the last few years while I've been playing a Vintage Sounds Classic 15 (PR clone, this one has a 10" speaker).

    Recently I've had the Princeton (Weber P10Q) out a couple times and it does not sound good to me. It sounds tinny and lacks depth. I've got the treble down to 3 and the bass up to 8.5 with the tone control on my guitar backed off half way. It is possible that my ears have changed, but as much as I used to love the sound of the Princeton, I think maybe I need to swap some tubes. I've tried a few different 12 AX7's (ECC83s) in positions V1 and V3. No change. Where first place I should start? The power tubes are old JAN and always sounded superb to me. Time for a different set? How do I know?

    Thanks. I'm not a tech oriented person, but I have a bias meter and know how to use that if I need to.

    Cheers,
    Ben

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  3. #2

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    Read up in this forum on adding a midrange control to the PR. At least one thread goes into significant detail.

    Any even remotely competent tube tech can do this easily.

    When in doubt go for AT LEAST a 25 K midrange pot as opposed to the more Twin-like 10K. There is no downside to this, and notable upside.

    The classic PR mod location for the added midrange pot is on the back in the Ext Speaker hole. Of course you can use one of the tremolo pot locations if you do not mind losing the ability to play “Crimson and Clover”

    Then look seriously at late breakup output tubes. I had remarkable luck twice with MESA (branded) 6V6 sets with a late breakup.

    But sure, it is also possible that your ear (more likely, brain) has changed its idea of what sounds good.

    Hope it all works out for you.

    Chris

  4. #3

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    If your vintage PR sounds different since being stored (semi retirement), and you've already swapped in new pre-amp tubes, I'd get new power tubes. Also the caps may need changing as well. Old tube amps can easily take you down the repair/maintenance rabbit hole. So start with the easy and inexpensive things. Hopefully that will awaken your beloved amp.

  5. #4

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    Please clarify, is this actually manufactured in 1968 or Fender’s recent 68 Princeton model?

    I doubt the tubes would change much as a result of age. Electrolytic caps do age. 50 year old electrolytics are almost certainly bad. 50 year old carbon composition resistors drift, and can fail catastrophically if they are in a spot that draws much current. Tube connectors can become corroded or loose. Solder connections can fail if they were poorly done.

    If you wonder if you’d like it better with a different speaker, try playing your PR through the VSA’s speaker, and play the VSA through the PR’s speaker (leaving them in their original cabinets). That should confirm whether you issue is with the amp or speaker.

    If you want a better idea of how a technician would go about diagnosing old tube amps, take a look at these videos.


    These guys do a nice job of summarizing their thought process as they diagnose and prioritize issues. And more often than not the tubes aren’t the main issue.
    Last edited by KirkP; 07-22-2019 at 02:24 PM.

  6. #5

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    That's what I would like to know: Custom 68 Princeton Reverb or a real deal 1968 Princeton Reverb?

    "Tinny and lacking depth" sounds like a bias problem. Let it cook a bit and check the bias of the 6V6s. What is the condition of the tube rectifier?
    Great Deals with Great Folks: max52 (Guild-Benedetto Artist Award); prickards (Ribbecke GC Halfling); Cincy2 (Comins Concert)

  7. #6

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    Thanks for the replies! I appreciate the thoughts and links KirkP.

    Yes, it's actually 51 years old, drip edge Princeton, very worn (well loved and played and gigged). I have the original Oxford speaker too, so I can try that one while I'm playing around with the amp. I had a cap job done back in the 90's.

    I'm going to start simply checking the bias on the 6v6s, then maybe try a different set. I'll probably put it up for sale when I get the sound sorted, so I'm not descending into any rabbit holes with this amp. I'll tell you, in this day and age with builders hand wiring amps and improving upon the old circuits, who needs vintage? I sold my mid 70's deluxe reverb: no regrets. What I'd like to go along with my Classic 15 is Rick's single channel version of the deluxe reverb. Anyway, that's all besides the matter at hand.

    Thanks all. Cheers,
    Ben

  8. #7

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    Spot on!!

    Quote Originally Posted by KirkP View Post
    Please clarify, is this actually manufactured in 1968 or Fender’s recent 68 Princeton model?

    I doubt the tubes would change much as a result of age. Electrolytic caps do age. 50 year old electrolytics are almost certainly bad. 50 year old carbon composition resistants drift, and can fail catastrophically if they are in a spot that draws much current. Tube connectors can become corroded or loose. Solder connections can fail if they were poorly done.

    If you wonder if you’d like it better with a different speaker, try playing your PR through the VSA’s speaker, and play the VSA through the PR’s speaker (leaving them in their original cabinets). That should confirm whether you issue is with the amp or speaker.

    If you want a better idea of how a technician would go about diagnosing old tube amps, take a look at these videos.


    These guys do a nice job of summarizing their thought process as they diagnose and prioritize issues. And more often than not the tubes aren’t the main issue.

  9. #8

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    I see the Vintage Sound Classic 15 has a mid control. Where do you leave that normally? Could make all the difference indeed.

    The suggestion to play the PR through the Classic 15´s speaker is a good one to find out if the difference is in the speaker.

    Or as suggested: the PR might need new caps, some CC-resistors have drifted in value (tubes don't deteriorate from not using them)

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  10. #9

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    Quote Originally Posted by thrush40 View Post
    Thanks for the replies! I appreciate the thoughts and links KirkP.

    Yes, it's actually 51 years old, drip edge Princeton, very worn (well loved and played and gigged). I have the original Oxford speaker too, so I can try that one while I'm playing around with the amp. I had a cap job done back in the 90's.

    I'm going to start simply checking the bias on the 6v6s, then maybe try a different set. I'll probably put it up for sale when I get the sound sorted, so I'm not descending into any rabbit holes with this amp. I'll tell you, in this day and age with builders hand wiring amps and improving upon the old circuits, who needs vintage? I sold my mid 70's deluxe reverb: no regrets. What I'd like to go along with my Classic 15 is Rick's single channel version of the deluxe reverb. Anyway, that's all besides the matter at hand.

    Thanks all. Cheers,
    Ben
    Glad you clarified that yours is vintage, not a reissue. I also own a '68 Drip Edge Princeton and love that little tone box. Good luck addressing the issues with yours.

  11. #10

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    I tried the Princeton's speaker (Weber P10Q) through the Vintage Sound amp and it sounds absolutely as it should: perfect, different, of course from the WGSG10C. When I plugged it back into the Princeton the amp sounds like an old mono transmitter radio. Yuck.

    I dropped the chassis to remind myself what I'd ordered replaced in the past. I also pulled my files to find the work invoice. Both confirmed replacement of the following in 1998:
    Aero filter can cap
    6 Sprague Atom 25uf-25v
    1 Sprague Atom 50uf-50v
    Plus the volume pot and power cord (which was still two prong at the time).

    There was also a full set tube replacement at the time. I may have replaced a few of the tubes since then, and even recently swapped some out when I was diagnosing a tube problem in the VSA.
    I would say the amp has had very light play time over the years since I bought it in about '93-'94.

    I'm tempted just to put in a set of new preamp tubes and see what happens. Thoughts?

    TIA!
    Ben

  12. #11

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    Swap the preamp tubes from the Princeton Reverb for the ones in the Vintage Sound 15. No harm done to try them.
    Great Deals with Great Folks: max52 (Guild-Benedetto Artist Award); prickards (Ribbecke GC Halfling); Cincy2 (Comins Concert)

  13. #12

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    Quote Originally Posted by Jabberwocky View Post
    Swap the preamp tubes from the Princeton Reverb for the ones in the Vintage Sound 15. No harm done to try them.
    yes, duh! That occurred to me immediately after posting and a very quick and easy test indeed.

    Done. The tubes are NOT the culprit. I checked/swapped them all. While messing with controls on the PR, I discovered the sass pot is nonfunctional! So, it's either the pot itself or what? Is there some resistor or cap associated with the bass pot that should be checked?

    Thanks to all you for following along and sharing your suggestions! I really appreciate it. At this point, I'll probably want a tech to do some testing. I don't have tools or skill set for fine soldering.

    Cheers,
    Ben
    Last edited by thrush40; 08-11-2019 at 01:50 PM. Reason: additional info

  14. #13

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    Could be a very dirty bass potentiometer, but usually that just makes the pot scratchy, not totally dead. You could try a high quality contact cleaner. (Not WD40!)

    Seems more likely it’s an open circuit between the bass pot and something it connects to, probably due to a bad solder joint. If you try to work on the innards yourself, you’ll need to educate yourself on safety around high voltage capacitors and on point to point style soldering.

  15. #14

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    Hi, I’m a tech. I’ll give you my priority list if this amp came to me.

    First yes the bass control. I’d spray that out as suggested but the symptoms suggest a blown cap in the tone stack. If a pot is bad/cruddy you’ll usually get intermittent/crackly operation.

    But it after that I would test the power tubes. If those are from the 90s you will definitely get a better sound with new tubes. And worn power tubes will definitely kill a robust bass response.

    Lastly, filter caps have about a 20 year max life span for vibrant tone. Again worn filters give you mushy bass (and weak highs).

    So so that would be mi recommendation for the whole 9 yards and getting this back to how it should be sounding.

  16. #15

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    Thanks so much.

    I'm dropping it off with a tech today. I'll post back with his assessment.

    Cheers,
    Ben

  17. #16

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    Quote Originally Posted by Little Jay View Post
    I see the Vintage Sound Classic 15 has a mid control. Where do you leave that normally? Could make all the difference indeed.
    Spot on there, Jay. Chances are very high that (perhaps among other things) is what the OP is experiencing

    FWIW I put a midrange control on my homebuilt 6L6/12" Princeton Reverb. It has the stock 6.8k resistor before the 15k pot, so 0 = factory scoop and 10 = more midrange. In that range (on the classic Fender preamp) the difference is subtle but noticeable. Add more midrange than that and things start getting kinda 'barky.' Your Results May Vary.
    "Don't worry about that. Everybody talks about finding your voice. Do your homework and your voice will find you." - Branford Marsalis

  18. #17

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    And sometimes, "barky" is what you want!
    Two thumbs up on adding a Mid control on the back. On my old PR, I have a mid control, and what I like about it is: with different guitars and diff. p/ups, you can really fine tune the sound and feel of the amp/guitars.

    But first, get the amp working up to snuff. Maybe the tech can add the Mid Control while it's on the bench?