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Post subject: Would you upgrade an 80s Princeton SF cab?
Posted: Fri Jun 06, 2014 4:15 pm
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So I'm considering buying a Princeton Reverb Silverface from the 80s. Thinking maybe I would upgrade the cab to a better built pine cab (Mojotone or Mather cab). Good idea or not?


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Post subject: Re: Would you upgrade an 80s Princeton SF cab?
Posted: Fri Jun 06, 2014 5:45 pm
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Good idea.

You might also consider a slightly taller enclosure that's configured for a 12-inch speaker. You'll find a greater selection of options among the larger drivers.

Save your original cab for "posterity".

Arjay

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Post subject: Re: Would you upgrade an 80s Princeton SF cab?
Posted: Fri Jun 06, 2014 6:02 pm
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Sounds good. Might just go ahead with that if I can get the Princeton for the best price. I figure the 80s SF are less collectable than the earlier years.


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Post subject: Re: Would you upgrade an 80s Princeton SF cab?
Posted: Fri Jun 06, 2014 8:50 pm
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TC5A wrote:
I figure the 80s SF are less collectable than the earlier years.


+1

Here's what I did with a 1980 non-verb Princeton......

Image

Yes, that's a piggyback conversion with the diminutive 12-watt amp driving a pair of 12-inch JBL's.

Arjay

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Post subject: Re: Would you upgrade an 80s Princeton SF cab?
Posted: Sat Jun 07, 2014 4:51 am
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Cool! Looks great.


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Post subject: Re: Would you upgrade an 80s Princeton SF cab?
Posted: Mon Jun 09, 2014 3:15 pm
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And plenty loud enough for any garage jam or small-club venue.

Arjay

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Post subject: Re: Would you upgrade an 80s Princeton SF cab?
Posted: Mon Jun 09, 2014 4:14 pm
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I have a 77 Princeton Reverb, same issue with the particle board cab. While a pine finger-jointed cab might sound better, there are other fun things to do to the amp.

Search for the Tonequest report "under 40 watts of whoopass" that talks about a few of the things to do.

Besides a new filter can, I did the phase inverter mod and the output transformer swap. Very happy and the Princeton Reverb loves to sing. Combined with a 1x12 extension cab and it's very giggable. And since it's a '77, I didn't feel bad about modding it. Down the road, I might invest in a pine cabinet, but I've got more things on my mind… like finding a wrecked Deluxe Reverb or Princeton and doing the Arjay Piggyback mod to it...


this is an article I found; can't remember where or the source, but good info for Princeton Reverb Fans. Arjay and the others please comment as I found this and did this way before I found you guys...

Quote:
In most Princetons, the limiting factor in power output is that the phase inverter starts clipping before the 6V6s. Once the PI clips, there is nothing left to push the 6V6s any harder. The tweak simply gives the PI a bit more dynamic headroom so that the 6V6s clip first. You simply move the B+ feed for the PI up one notch on the power supply voltage divider. Give it more voltage to work with, it's dynamic headroom increases, and now you can drive the 6V6s all the way. Leave the B+ feed for the remainder of the preamp stages alone. Move only the PI. Up one step. That's it. Very simple. You just move a wire.

http://www.people.cornell.edu/pages/...m/PRtweak.html
http://www.people.cornell.edu/pages/.../mm/boost.html


One other thing I did, which is optional, is that the voltages in the Princeton are a bit lower than in it's bigger brothers. Yet it uses the identical circuit to drive the reverb pan. The lower voltages result in a lower drive
level to the pan. IMO, the reverb sounds better if you can bump up the drive a tad. I did this by reducing the value of the 12AT7 cathode bias resistor from the nominal 2.2k to 1.8k. Running the tube at slightly higher current gives a tad more drive and livens up the reverb a tad. If you are happy with the way your reverb sounds now, just skip this.

You can also help keep it from farting out by reducing the value of the coupling cap feeding the input of the PI. That split load PI circuit topology has a VERY high input impedance (several megohms) since the grid leak resistor is returned to essentially half the load (in the cathode leg), which follows the signal. That very high input impedance along with the stock input cap value result in lots of low end crap getting through which you don't need. I recommend using 1/4 the stock value. cleans up the low end fartyness with no loss in "real" low end tone.

Speaker Recommendations
The stock speaker in these amps is a real limp-wristed turd. These amps respond amazingly well to a speaker improvement. The WeberVST C10Q seems to be the best choice, it can handle the (increased) power no sweat, it's WAY efficient (loudernhell) and had a vastly improved low end compared to the stock speaker. Yet it still has that classic Jensen style vibe. Try it, you'll like it.

You do all these tweaks, you'll end up with a nice little Princeton Reverb that will rattle windows and is usable for small gigs. Yet it still looks stone stock, and sounds the same as before, only LOUDER. All tweaks are very easily reversed. No Torres level hacks or butchery.


Output Transformer swap
One last item, and this is to be considered as an optional option (think long and hard before doing it), is to replace the stock (somewhat wimpy) output tranny with one for a Deluxe Reverb. The DR unit has more iron, and fits perfectly (there was a second mounting hole already in the chassis to accept the increased leg spacing). I just bought a generic replacement DR tranny from Mojo for mine. IMO, this is the way Fender should have built the PR, but I'm sure they didn't because it then becomes too close in tone and volume to a real DR, and they needed more product differentiation. Oh well....

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Post subject: Re: Would you upgrade an 80s Princeton SF cab?
Posted: Mon Jun 09, 2014 4:42 pm
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Great stuff, Nedo -- thanks for posting that.

I'd agree on all counts with a qualification to upgrading the speaker. Simply put, there is adequate room in a Princeton Reverb cab for a 12-inch speaker. And even with the larger driver, the amp does not assume the squelched-and-boxy timbre of the Blue Jr (oft-maligned for similar reasons). In the PR, a bigger speaker offers more sonic options.

(of course, I'm of the belief that if a twelve sounds good, a fifteen will sound great!)

:wink:

Rawk on!

8)

Arjay

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Post subject: Re: Would you upgrade an 80s Princeton SF cab?
Posted: Mon Jun 09, 2014 5:16 pm
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nedorama wrote:
Down the road, I might invest in a pine cabinet, but I've got more things on my mind… like finding a wrecked Deluxe Reverb or Princeton and doing the Arjay Piggyback mod to it...
[/quote]

Nedo, I like your thinking on this for sure. A wrecked Deluxe to turn into a head is something I have been thinking about. I was thinking about creating a 2x12 cabinet with a couple of Jensen C12Q's I have and pairing them with a Deluxe Head.
8)
T2

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Post subject: Re: Would you upgrade an 80s Princeton SF cab?
Posted: Tue Jun 10, 2014 4:51 am
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Push-pull 6V6GT amps make a great head unit. I think the Marshall 20-watt head (EL84) is one of their best, tone-wise. And plenty loud enough with the right speakers/cab, for most work.


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Post subject: Re: Would you upgrade an 80s Princeton SF cab?
Posted: Tue Jun 10, 2014 10:26 am
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BMW2002Ti wrote:
And plenty loud enough with the right speakers/cab, for most work.


+1

Speaker-system efficiency is something that often overlooked in the overall audio amplifier equation, likened to the gain factor of an antenna system used with a specific radio transmitter.

Arjay

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