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FDP Forum / Amp Mods, Repairs, and Projects / Princeton Mods, Bring 'Em On

Previous 20 Messages  
RivEraEra

usa/east bay sf

Ain't no time to hate
May 21st, 2008 09:48 AM   Edit   Profile   Print Topic   Search Topic

Thanks '58.

mbratch

Webster NY

May 21st, 2008 02:39 PM   Edit   Profile   Print Topic   Search Topic

(This message was last edited by mbratch at 02:40 PM, May 21st, 2008)

SoK66
Contributing Member

USA

We had the hit but Van got the money
May 21st, 2008 08:49 PM   Edit   Profile   Print Topic   Search Topic

" any links to the Stokes mod? I'm wondering if it's the same thing or similar to what Torres calls the Perfect prince mod. "

Not the same thing. Stokes mod moves the PI power feed to a lower resistance node of the filter cap can, increasing vltage to the PI. The Torres "Perfect Prince" kit supposedly balances the resistance of both sides of the PI using Dale resistors, and, IIRC, adds 470k screen resistors to the power tubes.

(This message was last edited by SoK66 at 08:50 PM, May 21st, 2008)

imjb1911
Contributing Member

Chicago

BFPR fan club member
May 22nd, 2008 08:00 AM   Edit   Profile   Print Topic   Search Topic

A lot of knowledgable people feel that the Stokes mod fixes a flaw in the original design of the Princeton. There is no good reason NOT to do it, JMO of course.

RivEraEra

usa/east bay sf

Ain't no time to hate
May 22nd, 2008 11:37 PM   Edit   Profile   Print Topic   Search Topic

I started to do to do the Stokes mod, but haven't tested it, got waylayed by other anomalies I found in there. The amp is a pull boost so I realize it's not a blackface circuit, but found a couple of things that didn't seem right. The most unusual thing was a .047 blue drop cap attached to pin 6 of the reverb driver tube (edit - I've never seen a blob type cap attached to a tube pin) and a 1.5M/22pF combo where the 3.3M/10pF combo usually are - unfortunately don't have a 3.3M resistor in my parts box so have to wait til tommorow to pop that in - I also pulled out the pull boost leads.

I also added a 47k resistor to the NFB, although it seems like I should be able to just replace the 2.7k altogether and just put the 47k in it's place.

(This message was last edited by RivEraEra at 11:39 PM, May 22nd, 2008)

rfrakes331K
Contributing Member
*******

IL USA

RonHalen Jokingly He Says
Jul 12th, 2017 03:50 PM   Edit   Profile   Print Topic   Search Topic


I am thinking of modding my plain Prince. I've looked at the Stokes mod, but unless you put in the beefier Deluxe OT, you may blow the stock OT. Then there is the Paul C. mod. And the Torres Perfect Prince kit. Torres has retired, but the kits are still available. I would like to take it to Tweed as i am not interested in more power, just better breakup, odd order harmonics. I don't see any Tweed mods out there though?

Paul C. and John Stokes mods

Hammond101
Contributing Member
**********

So. Cal. USA

Jul 12th, 2017 04:25 PM   Edit   Profile   Print Topic   Search Topic

rfrakes331K,

I don't see the value in modding a cool BF Fender amp, however....this is pretty non-invasive and reversible.

I think your best success would be playing with negative feedback resistor values to get the amp to break up a bit more. I believe the stock value is 2.7K ohms. You might try raising the value by 25% and 50% and see if you like the changes.

You can use your unused ground switch to switch resistor values if you have put in a three conductor power cord. This switch is then no longer needed.

rfrakes331K
Contributing Member
*******

IL USA

RonHalen Jokingly He Says
Jul 12th, 2017 06:45 PM   Edit   Profile   Print Topic   Search Topic

Thanks Hammond. It is a 75 Silverface Princeton non reverb. Anyone else? Any point in putting in a bias pot?

(This message was last edited by rfrakes331K at 08:46 PM, Jul 12th, 2017)

ejm

usa

Jul 13th, 2017 08:17 AM   Edit   Profile   Print Topic   Search Topic

FYI: FWIW, this thread was recently resurrected after 9 years dormancy.

And JMO, and not trying to be the vintage police or anything, but I would not mod any of the "collectable" Fender (or other) amps. And I guess that means we're getting older, because the 1970's and some 1980's Fender tube amps are collectable.

And if I did do any mods, I would make sure that they are reversible (for possible resale at some later point).


rfrakes331K
Contributing Member
*******

IL USA

RonHalen Jokingly He Says
Jul 13th, 2017 04:17 PM   Edit   Profile   Print Topic   Search Topic

ejm, I would agree, but the amp will stay in the family. Hammond has made a good reversible mod suggestion. I will start there. A 50% increase would be 4050 ohms. I could see a 50K pot stuck there as a Presence control like on the Bassman.

rfrakes331K
Contributing Member
*******

IL USA

RonHalen Jokingly He Says
Jul 13th, 2017 07:16 PM   Edit   Profile   Print Topic   Search Topic

But then, it has always lacked that Magic Fairy Dust Tone! In a YT Tweed Princeton, it had that Tone!

Hammond101
Contributing Member
**********

So. Cal. USA

Jul 14th, 2017 10:44 AM   Edit   Profile   Print Topic   Search Topic

Without major surgery the tweed front end ain't happening. Then you still have the SF power section. Want a tweed Princeton? I'd buy a kit and build one. (Actually I turned an old radio into a tweed Princeton)

Try the negative feedback thing 1st. You may be real surprised at what it does to make the thing hair up and sing.

What ever I would do, I would drill no holes.

rfrakes331K
Contributing Member
*******

IL USA

RonHalen Jokingly He Says
Jul 14th, 2017 07:22 PM   Edit   Profile   Print Topic   Search Topic

I did revive this old thread so as not to create another. What about modding a basement floater Blackface plain prince? It was a rusty mess when I got it. Many parts had to be replaced. So it is not all original or unmolested.

(This message was last edited by rfrakes331K at 07:58 AM, Jul 15th, 2017)

Hammond101
Contributing Member
**********

So. Cal. USA

Jul 15th, 2017 04:10 PM   Edit   Profile   Print Topic   Search Topic

Just my personal opinion but I like to return old non working amps to original as close as possible. Save maybe a neg feedback mod.

I'm doing a '79 PR at the moment for a customer. Somebody hacked it up pretty good in the past and turned it into a buzz saw.



rfrakes331K
Contributing Member
*******

IL USA

RonHalen Jokingly He Says
Jul 15th, 2017 07:48 PM   Edit   Profile   Print Topic   Search Topic

Buzz saw is not a desirable tone imho. So you can replace caps and bad resistors and that doesn't harm the originality? That is what I did and pots.

Peegoo
Contributing Member
**********
**********
******

The rain sounds like

a round of applause
Jul 16th, 2017 05:16 AM   Edit   Profile   Print Topic   Search Topic

As long as you (1) use quality components identical in spec to the original circuit, (2) do tidy work, and (3) retain the original caps and other parts in a little bag to include with the amp, the value is not reduced by much--if at all. If the buyer is going to play the thing, the value is increased because the amp is healthy, reliable, and sounding great.

rfrakes331K
Contributing Member
*******

IL USA

RonHalen Jokingly He Says
Jul 27th, 2017 07:42 PM   Edit   Profile   Print Topic   Search Topic

How about lowering the voltage with a variac?

Steve Dallman
Contributing Member
**********

Merrill, Wisconsin

Age is just a number...mine is big
Jul 29th, 2017 08:27 AM   Edit   Profile   Print Topic   Search Topic

I did the Stokes and Paul C mods on my 65 Princeton Reverb and kept both. No problems with the output transformer. I also changed to a dust cap modified Jensen C12N (new one) and love the result. I replaced the volume pot with a push pull pot, and wired in a bright switch, which I often use. It's my favorite amp.

I bought it at a pawn shop for $89. The cabinet and baffle were in rough shape, but the chassis and face plate were near perfect.

pdf64

UK

Aug 13th, 2017 02:37 AM   Edit   Profile   Print Topic   Search Topic

A potential problem with most variacs is that twist the knob the wrong way and they increase the mains voltage.
If you want to lower the power output a bit, consider a lossier rectifier tube, eg 5y3, 5R4.
That would also pretty much eliminate any chance of mods to the cathodyne mentioned above stressing the OT.

rfrakes331K
Contributing Member
*******

IL USA

RonHalen Jokingly He Says
Aug 30th, 2017 12:05 PM   Edit   Profile   Print Topic   Search Topic

Mine doesn't have a step up transformer in it. So I can't go up. The sound doesn't thrill me when the voltage is turned down.

Previous 20 Messages  

FDP Forum / Amp Mods, Repairs, and Projects / Princeton Mods, Bring 'Em On




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