From tremolu–(at)–ol.com Sat Sep 21 20:08:24 CDT 1996
Article: 23170 of alt.guitar.amps
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From: tremolu–(at)–ol.com (Tremolux)
Newsgroups: alt.guitar.amps
Subject: Re: Simple Princeton mods?
Date: 21 Sep 1996 19:07:36 -0400
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Juicing up a Princeton? Forget any hacks that require major butcher jobs.
Here’s some simple reversable mods that still keep it looking and
sounding like it’s supposed to.
1. – You might replace the stock wimpy output transformer with one from a
Deluxe, they’re beefier.
2. – Consider replacing the stock speaker with one that’s more efficient.
Stick with the 10″ to avoid a hack job, just get one that puts out more
dBs of sound for a given input power.
3. – The stock phase inverter circuit is kind of lame. You can get major
improvements by increasing the headroom. Do this by moving the supply
connection for the phase inverter to the next higher tap on the power
supply voltage divider. (Yeah, I’ve seen some that didn’t have enough
headroom to drive the 6V6s to saturation.)
4. – Install a set of good NOS tubes, and have the thing properly biased.
(This isn’t a mod).
5. – Have a cap job done if it needs it. (This isn’t a mod either)
A stock Princeton that’s totally healthy puts out about 18 Watts. Putting
in a more efficient speaker will gain you 1 or 2 dB. Putting in a Deluxe
output transformer should get you yet another dB. The result will be a
net gain of 2 to 3 dB in sound level, assuming everything else is
ship-shape. That’s about all you can do without resorting to unadvisable
hacking.
From tremolu–(at)–ol.com Thu Sep 26 01:10:10 CDT 1996
Article: 23490 of alt.guitar.amps
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From: tremolu–(at)–ol.com (Tremolux)
Newsgroups: alt.guitar.amps
Subject: Re: Simple Princeton mods?
Date: 26 Sep 1996 01:49:19 -0400
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>>>How much should the other mods cost?
Increasing the phase inverter headroom is a matter of moving a wire or two
inside the amp, say 15 minutes of bench time.
Replacing the output transformer with a Deluxe transformer costs about $40
for the transformer and another half hour or so of bench time.
Putting in decent preamp tubes you do yourself. You can get NOS 12AX7s
for about $15 each.
NOS 6V6s are uncertain. Whatever you pay for a matched pair, plus a
little more bench time for biasing.
From tremolu–(at)–ol.com Sun Nov 24 14:29:08 CST 1996
Article: 28435 of alt.guitar.amps
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From: tremolu–(at)–ol.com
Newsgroups: alt.guitar.amps
Subject: Re: Fender Princetons? are they any good?
Date: 24 Nov 1996 19:35:32 GMT
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You can get a little more poop out of a Princeyton if you want to do some
work on it. As Tim mentioned, the stock phase inverter circuit falls way
short on being able to drive the output stage all the way to saturation.
However, you don’t have to resort to such drastic mods as Tim talks about
to fix it. Basically, the stock phase inverter lacks sufficient dynamic
headroom to develop enough grid drive. That can be cured by moving that
stage’s B+ supply connection one step higher on the voltage divider in the
power supply. Increase it’s supply voltage, and you simultaneously
increase it’s headroom. Be careful to move only the phase inverter’s
supply to the next higher tap, and leave the remainder of the preamp where
it is. You’ll have to move a couple wires to do this. You may also,
depending on several variables, need to rebias the phase inverter by
changing the 1500 ohm bias resistor to 1200 ohms. Anyway, if you do this,
the thing will then (with little room to spare) be able to fully drive the
output stage. Be sure the output tubes are properly biased between 25 and
30 ma each at idle.
You can also change the output transformer to that from a Deluxe if you
want, it doesn’t hurt. I have two friends with a brown Princetons. In
both, I’ve put in the Deluxe transformer, and changed the 5Y3 rectifier
tube to a 5AR4 to give more voltage to the output stage. Those amps now
put out 18 Watts. I’ ve also done the phase inverter mod alone to a 64
Princeton Reverb, and it also now puts out about 18 Watts.
Lastly, unless you have the proper test equipment, maybe you should not
tackle this yourself, because you’ll need to look at the actual effects of
your work using an o-scope to make sure you’re achieving your goals.
