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Post subject: Auction find: '66 Princeton
Posted: Sun Jun 03, 2018 1:54 pm
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I went to an auction yesterday with the hopes of getting a nice Gibson ES345 that was advertised, but it ended up going for more than I was comfortable spending. However, I did end up winning this amp, not even knowing it was at the auction prior to showing up. I gave it a quick once over when I arrived, but didnt have time to really date it, let alone try it out to make sure it works.

I got it for a very good price with the intent of selling it for a profit. I have a family member who builds tube amps, so I took it to him before I fired anything up. He ran all of his tests and said it seemed to work perfectly. We fired it up and oh my gosh, was that the sweetest guitar tone I've ever heard! I'm not sure I can sell it now.

I am a bass player, and I'm pretty rough on guitar, but this amp makes me want to get better. Everything on the amp appears to be original except for the tubes. The transformers date back to 66, and the circuit board looks unmolested. It has the molded blue coupling caps as well:

Here are some pictures:
Image

Image

Image

Image

Image

Image

Image

Image


What can you tell me about this amp that I should know?

Should I change the speaker? This amp will just be for home use, but I would like to use overdrive and some fuzz.


The only other things I'm curious about, are if I should change it to a 3 prong electrical plug, and I also notice their is minimal volume when the volume knob is all the way down. Then I don't notice any increase in volume until I get to 3.


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 1:36 am
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Lammchop93 wrote:

The only other things I'm curious about, are if I should change it to a 3 prong electrical plug, and I also notice their is minimal volume when the volume knob is all the way down. Then I don't notice any increase in volume until I get to 3.


AA964 (fall of 1964-1967)

http://ampwares.com/amplifiers/fender-b ... princeton/

Check if the fuse is the right one, many people over year put a too poeerful fuse wich could do big damage your amp

+100 to replace 2 prong cable
Always minimal Volume ;
1-Clean volume pot with good electronic contact cleaner ( Deoxit ). Poor quality one may not do the job.
2-Check volume pot ohms.

Low volume; check and replace bad tubes.
New 6V6s may need a bias adjust. A mod on bias circuit to add a pot could be very useful.

Some people will suggest to replace filter caps and all electrolytic caps ( the big brown ones) . I don't if amp play well and filter caps check good on good capacitor tester.
I use Heatkit IT-28 Capacitor Checker.

If you do, keep all original parts and use only good quality caps ( Sprague Atom .Mallory or F&T )

Never replace the blues signal caps, they are great for the tone
All 100 K resistor on 12AX7 or 7025 may need to be replace if you hear some hiss from the speaker.
I'll keep the speaker.


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 2:11 am
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The "PJ" stamped on the tube chart indicates a December 1966 date of manufacture. The chassis itself was completed during the 41st week of that year. Look for a corresponding EIA code on the speaker to determine its originality.

The power plug and two-conductor cable MUST GO. It's unsafe to operate the amp in its present condition. Likewise, dump the "death cap" and bypass the polarity (ground) switch altogether. The smart move would be to replace ALL of the electrolytic caps. That's those in bypass circuits, the bias supply, and the cylindrical metallic cap can. As well, inspect all of the carbon-comp resistors for signs of thermal fatigue and replace any that look "toasty". To engage the tremolo circuit you'll need the footswitch or a shorting plug. Once you have the amp safely up and running you can determine whether or not a speaker upgrade is warranted. The OEM Oxford (or Utah) speakers furnished in these amps are not particularly tone-worthy. Save all removed parts for "posterity".

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 3:17 am
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Your family member who builds tube amps may help you.

First thing to do;
Check fuse and replace 2 prong power cable.


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 3:19 am
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Retroverbial wrote:
The "PJ" stamped on the tube chart indicates a December 1966 date of manufacture. The chassis itself was completed during the 41st week of that year. Look for a corresponding EIA code on the speaker to determine its originality.

The power plug and two-conductor cable MUST GO. It's unsafe to operate the amp in its present condition. Likewise, dump the "death cap" and bypass the polarity (ground) switch altogether. The smart move would be to replace ALL of the electrolytic caps. That's those in bypass circuits, the bias supply, and the cylindrical metallic cap can. As well, inspect all of the carbon-comp resistors for signs of thermal fatigue and replace any that look "toasty". To engage the tremolo circuit you'll need the footswitch or a shorting plug. Once you have the amp safely up and running you can determine whether or not a speaker upgrade is warranted. The OEM Oxford (or Utah) speakers furnished in these amps are not particularly tone-worthy. Save all removed parts for "posterity".

Arjay


Just curious, why would I replace the electrolytic caps if the amp works fine?


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 6:55 am
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The electrolytic "fluid" dries up over time. The ESR rises and the capacitors ability to do what it is supposed to do diminishes. Useful life of an electrolytic capacitor is about 15 to 20 years or less. Yours are 52 years old. The amp will sound better when the power and bias supply have fresh caps for filtering. Fresh bypass caps will ensure the gain and frequency response of the preamp stages are working as designed.

Quote:
To engage the tremolo circuit you'll need the footswitch or a shorting plug.


The tremolo circuit on this amp should work without the footswitch or shorting plug.

The volume pot gets its ground from the chassis, make sure it's securely fastened. If it is loose, tighten with a hollow shaft nut driver to avoid scratching the faceplate.


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 7:47 am
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Are the capacitor kits from amprepairparts.com good quality? Looks like CE manufacturing brand capacitor.


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 8:07 am
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vinyl wrote:
should work without the footswitch or shorting plug.


+1

My bad, you are correct. The switch (or shorting plug) is necessary only to turn the tremolo OFF.

:oops:

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 8:32 am
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Lammchop93 wrote:
Are the capacitor kits from amprepairparts.com good quality? Looks like CE manufacturing brand capacitor.

That kit, I think is for the Princeton Reverb model. Different schematic than the amp you have and you would have leftover parts from the kit and no new "cap-can" a modification.
I think you would be better off replacing components individually.
https://www.tubesandmore.com/search/node/40%252F20%252F20?cats%5B0%5D=112
You need these electrolytic capacitors iaw AA964 schematics.
1ea 40/20/20uf x 500vdc cap-can
1ea 25uf x 50vdc
3ea 25uf x 25vdc

To me it looks like your cap-can was already replaced, a pic w/ all the numbers would be nice to confirm.


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 10:22 am
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sfceric64 wrote:
Lammchop93 wrote:
Are the capacitor kits from amprepairparts.com good quality? Looks like CE manufacturing brand capacitor.

That kit, I think is for the Princeton Reverb model. Different schematic than the amp you have and you would have leftover parts from the kit and no new "cap-can" a modification.
I think you would be better off replacing components individually.
https://www.tubesandmore.com/search/node/40%252F20%252F20?cats%5B0%5D=112
You need these electrolytic capacitors iaw AA964 schematics.
1ea 40/20/20uf x 500vdc cap-can
1ea 25uf x 50vdc
3ea 25uf x 25vdc

To me it looks like your cap-can was already replaced, a pic w/ all the numbers would be nice to confirm.


Here's a couple pictures of the cap. Looking at the code, I think it's a 1966 as well:
Image
Image

That website has a kit for the princeton non-reverb it says. The FCK-15 seems to be the one: http://www.amprepairparts.com/capkits.htm


Last edited by Lammchop93 on Mon Jun 04, 2018 10:56 am, edited 1 time in total.

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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 10:24 am
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vinyl wrote:
The electrolytic "fluid" dries up over time. The ESR rises and the capacitors ability to do what it is supposed to do diminishes. Useful life of an electrolytic capacitor is about 15 to 20 years or less. Yours are 52 years old. The amp will sound better when the power and bias supply have fresh caps for filtering. Fresh bypass caps will ensure the gain and frequency response of the preamp stages are working as designed.

Quote:
To engage the tremolo circuit you'll need the footswitch or a shorting plug.


The tremolo circuit on this amp should work without the footswitch or shorting plug.

The volume pot gets its ground from the chassis, make sure it's securely fastened. If it is loose, tighten with a hollow shaft nut driver to avoid scratching the faceplate.



The volume knob does seem loose, but when I open up the amp, the pot isn't spinning like it normally would if I was lose. There seems to be a little bit of extra turn in each direction after the pot shaft reaches it's "ends". Is this a bad pot?


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 11:02 am
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Ok, looks original! The real difference would be the smaller caps in the kit. I prefer the Sprague atoms or F&T over the IC's for about the same prices.. Nice amp by the way.

Also, the cap-can looks like its a PR can(20/20/20/20) instead of the 40/20/20 & wiring.
Great reference:
https://sites.google.com/site/jmasterschematics/


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 11:14 am
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sfceric64 wrote:
Lammchop93 wrote:
Are the capacitor kits from amprepairparts.com good quality? Looks like CE manufacturing brand capacitor.

That kit, I think is for the Princeton Reverb model. Different schematic than the amp you have and you would have leftover parts from the kit and no new "cap-can" a modification.
I think you would be better off replacing components individually.
https://www.tubesandmore.com/search/node/40%252F20%252F20?cats%5B0%5D=112
You need these electrolytic capacitors iaw AA964 schematics.
1ea 40/20/20uf x 500vdc cap-can
1ea 25uf x 50vdc
3ea 25uf x 25vdc

To me it looks like your cap-can was already replaced, a pic w/ all the numbers would be nice to confirm.


Also, it looks like my amp currently has:
1ea 20/20/20uf x 450vdc cap-can
1ea 50uf x 50vdc
3ea 25uf x 25vdc

Should I keep what is currently in it?, rather than what you listed above or what is offered with the cap kits on most stores?


Last edited by Lammchop93 on Mon Jun 04, 2018 11:46 am, edited 1 time in total.

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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 11:28 am
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No problem swapping w/ like original components.
Your original can is 20/20/20/20 x 450vdc, a higher voltage rating is no problem and w/ higher house outlet voltages 500 or 525 is fine as you will get higher voltages to the rest of the circuit than what is on the original schematics.
The bias voltage capacitor on the original schematics is 25ufx50vdc, your amp has a 50ufx50vdc. No problem w/ a 50ufx50vdc or 50ufx100vdc. The bias voltage is about -33 depending on tubes and such.
The 3- 25ufx25vdc cathode capacitors should be replaced w/ the same usually unless your trying to alter the tone somewhat and 25ufx50vdc is also not a problem.
I was probably editing my previous response, when you asked.


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Post subject: Re: Auction find: '66 Princeton
Posted: Mon Jun 04, 2018 11:36 am
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You'll notice the cap can has 1 unlabeled prong(20uf) connected to the adjacent prong via 18k resistor, that's the 4th 20uf your not realizing.

Also, upgrading to Sprague atoms and buying the 2w metal oxide dropping resistors(18k & 1k) separately would bring the price up to about $50 + shipping.


Last edited by sfceric64 on Mon Jun 04, 2018 11:51 am, edited 1 time in total.

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