Princeton Reverb II?

[reddinis]

Princeton Reverb II; schematic or circuit diagram

The amp works fine for clean tones. I'm working with the clean channel only. Right now it's in stock form. If I run any type of guitar and any type of overdrive through it for distortion, it sounds lousy. The cleans sound great, I couldn't be happier. But the amp can't handle distortion at all. It's very fizzy, even with the treble turned down. If I play a 7th chord on the low E, A and D string, it sounds like trash. I don't know if you'd call it fizz or oscillation, but it's the low notes that sound bad.

I've gone through tube swapping a lot, and I'm sure the tubes are all good. I did a cap job. The speaker is a Jensen Electric Lightning, which was designed for distortion (and it's a great sounding speaker, too).

I said it's all stock, but I added 1k screen resistors and an external bias pot and a test point for each tube (6V6's). I changed some of the power supply resistors to 5 watt, and upped the wattage on another resistor that is supposed to cause problems in this amp.

I've tried a lot of things in the pre-amp, but now it's back to stock. My amp came with a 1200pf plate to cathode cap on V1a instead of 500pf like shown in the schematic.

It acts the same with the reverb tube removed. I'm not concerned with the reverb or amp's overdrive at all at this point.

Any ideas would be appreciated. I'm at a loss.

[JoeM]

Try removing the 22pf cap in parallel with the 3.3M. (Other Fenders, non Rivera models, use 10pf.) That might at least lose some of the fizz. Maybe this amp just doesnt have a good OD sound.

[reddinis]

Try removing the 22pf cap in parallel with the 3.3M. (Other Fenders, non Rivera models, use 10pf.) That might at least lose some of the fizz. Maybe this amp just doesnt have a good OD sound.

Thanks for the reply.

It sure doesn't handle overdrive very well, but it's basically in stock form, I don't know. I have replaced all of the ceramic caps in the preamp with silver mica, but I will try to remove that 22pf, I was just looking at that.

I've also tried a 12AT7 in V1 and V3, didn't help.

The preamp looks to me to be very similar to the older Fender designs. I'm wondering if it's in the phase inverter or power amp, but I don't know how to trouble shoot those besides just swapping parts.

Also, I've cleaned and re-tensioned the sockets and the voltages are spot on.

I'm thinking about just wiring the phase inverter and power amp like a Deluxe Reverb. I don't know what to do.

I changed the cathode resistor bypass cap on V1 to 5uf and it didn't help. I lost bass, but it still fizzed out. I'm surprised at how much bass this thing has. I thought the small coupling caps would limit that?

[JoeM]

I wouldn't try modding it, if it just doesn't work for you. There seems to be a pretty good following for these Rivera Fenders. I'd sell it (stock) and get something that gets the sound you're looking for.

[reddinis]

I wouldn't try modding it, if it just doesn't work for you. There seems to be a pretty good following for these Rivera Fenders. I'd sell it (stock) and get something that gets the sound you're looking for.

Thanks for the reply.

Ha, ha, well I've already modded the hell out of the preamp but it's back to stock now. It had one minor mod when I got it.

Anyway, I think the problem is the front end being too hot, and then the phase inverter and/ or power amp not handling it well. I'm still trying to only correct the problem in the preamp.

One guy's running a 12AY7 in V1, another guy a 12AT7 in place of the AX7 phase inverter.

Can I ask you what effect the 10 meg and 1 meg resistors on the pull-mid and bright switch have?

[Edit:] I thought those would just look like an open circuit?

Thanks for your help. I'm going to mess with it some more.

[gbono]

Compare this design to the Deluxe Reverb - very similar if you remove all the additional "features" added to the PR II. If you measure the signals between V3 and the output (dual trace mode on a scope) you will seel this amp clip terribly when overdriven. I just worked on one of these and I believe matched output tubes are a must and I used a 12AU7 at V4 (PI).

[JoeM]

....

Can I ask you what effect the 10 meg and 1 meg resistors on the pull-mid and bright switch have?

[Edit:] I thought those would just look like an open circuit?

Thanks for your help. I'm going to mess with it some more.

The resistors just eliminate a 'pop' when the switch is activated. (From DC on the Caps)

[reddinis]

The resistors just eliminate a 'pop' when the switch is activated. (From DC on the Caps)

That's what I thought, thanks.

Compare this design to the Deluxe Reverb - very similar if you remove all the additional "features" added to the PR II. If you measure the signals between V3 and the output (dual trace mode on a scope) you will seel this amp clip terribly when overdriven. I just worked on one of these and I believe matched output tubes are a must and I used a 12AU7 at V4 (PI).

Thank you! I know a lot of people love these stock, but this one has issues. I knew I wasn't imagining things.

I dont have an oscilloscope, but I'm glad you saw what I'm hearing.

Okay, this is what I did, and I think this goes along with what you're saying. I was finally convinced that it was just too much gain, so I put a 450k resistor on top of the master volume. It didn't help the fizz much, just lowered the volume. Then I changed the plate resistor on V1a to 68k, and it killed the fizz. I then removed the 450k, and the fizz came back. Does that sound right? Those two mods combined killed the fizz? And this was with a 12AT7 in V1.

So, anyway, I think I will be trying what you did. The gain has to be cut down somewhere.

Did the amp lose a lot of volume with the 12AU7?

Do you think that if the 100k feedback resistor (and the long-tail pair and presence) was changed to a lower value it might help? What if I made it like a Bassman?

I thought about putting a 100k on the input of V1a instead of instead of 68k. Does that sound like a bad idea?

I don't have a 12AU7 right now, but I will be getting one. I'll probably just wait for that.

With the V1a plate resistor at 68k, it helped kill the fizz, but the amp lost its sweetness. I guess I would need to adjust the cathode resistor/ bypass cap? Is that a bad idea for any reason?

Thanks for your help. I can't wait to get an AU7.

[reddinis]

Well, I changed the NFL and phase inverter to look like a Bassman, and it's 90% better. I had to stop working on it because it's late. But, I'm not just saying it sounds better because I worked on it. I've been dealing with this for a while and I know what it sounds like. I'm 90%, maybe 95% there. I'm pretty sure I'll be able to finish it off tomorrow, and then figure out if the Lead channel is worth working on. These are killer sounding amps - big, full, and touch sensitive.

Thanks for your help.

[Gtr_tech]

The tone stack is after the first stage, so it's not well suited to a good overdrive sound. There will be harmonics generated after the TS that you can't shape via the tone controls. So farty and/or fizzy tonality is common with this design. Mar$hall got it right when they put the tone stack after all the gain stages (master vol 2203/2204, JCM800).

If there's a loop available, an EQ pedal can tame the fizz, but any odd artifacting from too much low end be'n shoved thru the gain structue will remain.

[gbono]

I noticed that the PI plate voltage is lower on the PR II design than say the deluxe reverb - have to assume this will effect the PI "headroom" and may explain the nasty clipping in the output stage.