Princeton Reverb w/Paul C-Stokes mod seems a little stiff

[RMcFarland]

Anyone have experience with these mods in a PR? My setup is JJ 6v6 tubes, various NOS pre tubes, tele in V1, mullard rectifier, and a Weber Cali 12" with paper dust cap.

I got the mods done last week. It seems a little too stiff. any ideas?

[Jeff Flowerday]

I'd get the Stokes mod reversed, it raises the voltage throughout the circuit and the cause of the phenomenom you are experiencing. There is also a slight danger of damaging your output tranny if play cranked all the time with it.

The Paul C really helps smooth out the gain, leave it in.


.02

[fullerplast]

The combination of the Stokes mod and the JJ 6V6's will tighten up the amp. Try some RCA's in there and see if it doesn't help. Otherwise, take out the Stokes mod if you liked it better before.

[hasserl]

The mod raises the voltage to the PI, I don't think it increases the voltage thruout the circuit. I've done the mod on my PR, but I didn't check the before & after voltages of the preamp, so I can't say from first hand experience, but I don't see why it would. Also, there has been some talk about this possibly being dangerous to the power tranny, I haven't heard it was dangerus to the OT, and again, I don't see why it would be.

And FWIW I've played mine fairly regularly at practices and gigs with no problems, as have a lot of other people.

But I agree with fullerplast; if you don't like the effect, take it out.

[Don L]

I don't think the Weber Cali is helping out much there...

[Jeff Flowerday]

Originally Posted by hasserl

The mod raises the voltage to the PI, I don't think it increases the voltage thruout the circuit. I've done the mod on my PR, but I didn't check the before & after voltages of the preamp, so I can't say from first hand experience, but I don't see why it would. Also, there has been some talk about this possibly being dangerous to the power tranny, I haven't heard it was dangerus to the OT, and again, I don't see why it would be.

And FWIW I've played mine fairly regularly at practices and gigs with no problems, as have a lot of other people.

But I agree with fullerplast; if you don't like the effect, take it out.

Doh! I meant power tranny. The extra voltage at the PI causes the PI to run more efficiently and drives the power tubes more causing them to draw more current which intern stresses the little power tranny.

I thought the the plates of the preamp tubes were affected by this change as well, can't remember if the plates of the gain stage preamp tubes are attached right at the cap can after the 18K or daisy chained from the top of 56k PI plate resister.

[Crazyquilt]

When I got my PR, it had those mods, and a Weber Cali, as well as the original GE tubes (or NOS in good condition; I'm not sure, but you get the idea.) It sounded very stiff & hard. I changed the speaker to a Weber 10F150T, and the problem was solved.

In terms of comparing JJs & other NOS tubes, I popped my GEs into my Swart AST, to see how they compared to the stock JJs. Much, much looser & rich (not that the JJs are bad by ANY means.) I can only extrapolate that, by reversing the process, the JJs would be too clean/tight/hard for the PR.

I'd try either some NOS tubes or a speaker upgrade, personally. Both, if you can swing it.

[ChrisP]

Originally Posted by Crazyquilt

When I got my PR, it had those mods, and a Weber Cali, as well as the original GE tubes (or NOS in good condition; I'm not sure, but you get the idea.) It sounded very stiff & hard. I changed the speaker to a Weber 10F150T, and the problem was solved.

In terms of comparing JJs & other NOS tubes, I popped my GEs into my Swart AST, to see how they compared to the stock JJs. Much, much looser & rich (not that the JJs are bad by ANY means.) I can only extrapolate that, by reversing the process, the JJs would be too clean/tight/hard for the PR.

I'd try either some NOS tubes or a speaker upgrade, personally. Both, if you can swing it.

..

I have the 10f150 w/both mods done by Dave Allen (allenamps.com) and it is not stiff...man I love that amp!

[Crazyquilt]

The mods on mine were done by Allen for the previous owner. If I wasn't clear, I never thought it was the mods, but, rather the speaker. I love mine, too!

[RMcFarland]

cool feedback guys!

my mods were done by a very respected amp tech in NJ, and I firmly believe in his work as many others do.

I think I am going to go the route of a speaker change. Can anyone comment on why the 10f150 is the best choice? I have heard this many times. Why not a lower watt or an Alnico?

[Wayne]

I tried the mod on my Princeton Reverb and reversed it.

Wayne

[RMcFarland]

can you elaborate on that?

[Jeff Flowerday]

Originally Posted by RMcFarland

cool feedback guys!

my mods were done by a very respected amp tech in NJ, and I firmly believe in his work as many others do.

I think I am going to go the route of a speaker change. Can anyone comment on why the 10f150 is the best choice? I have heard this many times. Why not a lower watt or an Alnico?

Actually go with the 25 watt 10F150T lightly doped. The 10F150T has a 125 cone with the bigger 150 magnet. ie) it's P10N with a P10Q cone. That translates into big bottom end, loud but a little softer feel than the straight 10F150.

Jeff