a redesign based on the Princeton Reverb II

This is more than a modification really... it's a simplification of the circuit, invented by Jon Hundt in the Netherlands and reported to me by Scott Murray in the US. They have both done this rebuild. There aren't any sound clips available yet but Scott tells me it approximates to the sounds shown on reviews of the Fender '65 Deluxe Reverb Re-Issue. Scott is prepared to answer questions - email him on smurray (at) taskpartner (dot) com.

" I bought the PRII new in 83 but was never really satisfied with it. I thought the "lead" channel sounded bad, and the clean channel didn't live up to the Fender legend. Before I bought it I had a blackface Bassman, and a blackface Super Reverb, so I knew what a proper Fender should sound like to me.

I looked at the schematic and noticed that the amp had a Deluxe-Reverb output transformer and choke, and that the reverb transformer was the standard Fender unit. The schematic was a mass of components - I had never learned to read electronics at that point. But by comparing the PRII to a Deluxe Reverb schematic I soon saw that the whole DR circuit was in the amp (except the vibrato part). The problem, it seemed to me, was that there were way too many other parts that were NOT on the old AB763 circuit.

I removed all the surplus parts, stripping the amp down to the basic Fender blackface circuit. I took out all the switching parts, since I never used the footswitch anyway. I changed a few component values to match BF specs. I kept a few features, like the mid-boost, the master volume, the line-out. I wired the "Lead Volume" pot as a variable resistor on the tail of the tone stack so that the tone circuit can be disabled - adding a great amount of gain and a whole lot of midrange, if desired. This is similar to the Allen Amps "raw" control. I wired the Presence control more like the old 5F6A bassman version. I added a bias adjustment pot. I also changed the speaker to a Celestion Vintage 30 (and added a Weber Beam Blocker).

The amp now sounds really good. It is basically a blackface Deluxe Reverb without the vibrato/tremelo and without the Normal channel.

I ran 6L6 tubes for several years, and they sounded great. I was a bit worried about the extra current draw, but nothing ever broke down. Lately I switched to JJ 6V6s and they sound just about the same as the 6L6s.

The mods were almost all non-destructive, and I utilised the existing black fiber eyelet-board. I still have a bag full of the parts I removed.

In those days a PRII wasn't considered valuable or collectible; I already owned it and it didn't satisfy me, so I didn't mind modding it. These days it might put some people off because most people seem to think we shouldn't change Fender amps.

I am attaching my current schematic and the original so that you can compare them and see what I did. ( I may have to send a following email with the original, my email program doesn't seem to like sending both at the same time). On the drawing I have labelled in red the parts that I changed values. Also, since I made that drawing I have removed the ground switch and cap, and the AC receptacle; and I substituted an Allen TO26 output transformer. This wasn't so much to improve the sound, but to give me an option to switch impedance depending on what kind of tubes I have in there.

If you superimpose the modified circuit over the original (on a light table, or taped up on a window, that's how I do it) you will see clearly all the parts that I removed.

I'm not really sure I would encourage anyone to do this to a PRII these days, as they seem to have become collectible. But it sure worked for me. Everything is reversible - though it's such a rat's nest in there, compared to older Fender amps, it would probably be pretty confusing. And, from the outside, the amp appears completely stock."

I made his (Jon's) changes, and in blue you can see a few of my further changes. Thus, that schematic is my amp.

I now own the most gorgeous sounding amp in the world. It sings like an angel.

And it's almost impossible to find a bad knob setting. I could let a two-year-old kid play with the knobs and it would still have a good sound.

Even with the junkie original speaker (remember I had the heavy upgraded speaker), it rocked. Then as a treat I installed a Celestion G12H and it is out of this world.

I did the changes one component at a time, starting in the preamp section, and played the amp a lot between each change. I was apprehensive at the start, but after just a few changes, the amp started to sound warmer. So I kept going, one change at a time. It took weeks to get all the way through, but at no point did a change make it sound worse; it just kept getting better."

So... here's the schematic for what they're recommending. As noted above, the changes in red are Jon Hundt's work and the blue changes are by Scott Murray. I have added further notes from Scott below the schematic in which he explains some of his component-value changes. I thank them both for getting in touch. If you try this circuit, or any part of it, let me know what you think of it.

"I had the same PRII experience that Jon wrote about: I bought the PRII new in 83 but was never really satisfied with it. There were a small number of knob settings that sound "OK", but it took a lot of hunting to find them. Then in early Jan 2013, I found an old guitar forum post from a jhundt that said this about his PRII: I bought one brand-new in '83, and I was disappointed. I didn't try it out in the shop; I just thought "it's a Fender, it will sound good" It was very sterile when clean, and the boost was not useable (for me).

Jon went on to write: "In the end I removed half of the stuff on the circuit board and changed some of the parts that were left. Hidden inside that amp is "the amp Fender never made" - a single-channel Deluxe Reverb w/ mid and presence controls, a master volume and more. And w/ 6L6s it sounds really nice."

I contacted Jon, and he graciously sent me his schematic. After we corresponded a few times, I thought it was worth a try. I felt my PRII was not a classic or a collectable, and I recognized the value of the point-to-point design.

After just a few changes (mostly removing caps in the preamp), the amp started to sound warmer. So I kept going, one change at a time. It took weeks to get all the way through, but at no point did a change make the amp sound worse; it just kept getting better.

I can't stress that enough that I did the changes one component at a time, and played the amp a lot between each change. If you remove a lot of parts at once and then your amp won't work, or you don't like the new sound, you might be in trouble.

In the end, I made Jon's changes (in RED), and in BLUE you can see a few of my further changes. Any components on the original PRII schematic that you don't see here were removed and not replaced.

Jon uses 15k as the input resistor. I didn't have a 15k when I started, so I used the closest I had (22k). When I finally put a 15k in there, I thought the 22k sounded better and put it back.

I originally overlooked the removal of that 100pf cap across the preamp volume pot. It's mounted on the pot and was hidden under the lip of the chassis. When I finally noticed it, and removed it, my amp lost a little of its "sparkle". So I put it back.

With that discovery, I thought "if the 100pf adds sparkle, maybe another cap will add something too". So I added a .003uf cap in parallel with the 100pf, and made it switchable via pulling the volume knob (formerly the Lead switch). Pulling that switch now makes the amp more "aggressive". I'm going to get a few more caps of various values and try them there.

I couldn't add the Lead pot onto the Middle pot at this point, because the Lead circuit was still intact. That happened later.

When I had completed with the preamp section changes, my amp already sounded much "warmer". Even if I had stopped there, and made no more mods, it would have been worth the effort. However, I was encouraged by the warmer sound to keep going.

Jon used a standard Fender value .022 as the coupling cap into V4A. Once again, I left the original .01 in there until I could get a .022. When I finally obtained and installed a .022, it did not sound as good to me as the original .01, which I re-installed.

In the reverb section (lower left), I followed the same method, removing one component at a time and playing a lot to see if I liked it. There was nothing earth-shattering there, although you can see Jon move the "B" voltage point and I did not. It's so crowded over in that corner by the can-cap and I was just too lazy to mess with it all. Can you believe that? The guy was nice enough to give me a map to paradise and I only took the easy steps. Typical American, huh?

In the Lead section (V3A) it was not practical to remove one component at a time. If you look at the two optocouplers (013556), you see there are eight legs between them, and you can't really remove one without removing the other. This observation, plus my hatred for the Lead sound, plus the confidence I had from the positive changes so far, gave me the impetus to do a full-scale assault on the lead section. I did all of that in one fell swoop. I left the components in place, but lifted enough leads to disable the circuit. And that includes disconnecting those 2 watt 390 ohm resistors from the bias circuit.

When I played the amp with the Lead section disabled, it sounded great so I went back and removed the unused components. And the Lead pot freed up, I was then able to connect it to the bottom of the tone stack in the preamp section. That opens up a whole new range of sounds to the amp.

Off of the wiper of the reverb pot, Jon uses a standard Fender value of 470k. Once again, I didn't have the 470k so I left the old 1.2M in place. When I finally installed a 470k, the 1.2M sounded better to me so I put it back.

And it's almost impossible to find a bad knob setting. I could let a two-year-old kid play with the knobs and it would still have a good sound.

Even with the junkie original speaker (I had the heavy upgraded speaker), it rocked. Then as a treat I installed a Celestion G12H and it is out of this world.

I don't have the equipment to make a decent recording to post here, but my amp sounds a lot like this youtube demo of Fender Deluxe Reverb Reissue (except mine has no tremolo):

I would be glad to help anyone who is considering this idea."

(end of Scott Murray quote) Once again, big thanks to Jon and Scott.

As with all the other pages on my site, the details are believed correct but I won't take any responsibility for what happens if you attempt them. Valve/tube amps store lethal voltages even when switched off and unplugged from the wall, and if you don't know what you're doing, you can be badly hurt.

If you have tried any modifications, I would be delighted to hear from you - even if you're not satisfied with the result, it's useful information for the rest of us! I'm specially interested if you've converted to cathode bias, converted to tube (valve) rectification, or added a sag resistor.