Discovering some mods in a 65 DRRI 2013 & tremolo question

[joulupukki]

While contemplating an upcoming possible RR763V 6V6 Blackvibe build, I came across a decent deal on a used (2013) Deluxe Reverb Reissue in my local classifieds and couldn’t pass it up. I actually did the same thing when I built my Mojotone Princeton Reverb (bought a PRRI as a reference and sold it after I had finished my build).

It plays wonderfully and part of my reasoning for picking it up was to know whether I wanted to proceed with the hand-wired Blackvibe build. But, the tremolo doesn’t sound nearly as incredible as the tremolo on my Mojotone PR. So, I popped it open this morning with the intent to change the two tremolo capacitors to at least have the option to slow down the tremolo a bit more.

That’s when I discovered a few modifications have been done on this amp (very cleanly, thankfully).

From what I can see so far, the mods so far are:

- Plate and cathode wires from the board to the tube sockets of V1, V2, and V3 are twisted together (I assume to help in removing hum)
- Bright cap on Vibrato channel is removed
- A small capacitor has been added in parallel to R28 (the first resistor going to ground after the signal comes back from the reverb tank)
- A capacitor has been added across the opto-isolator (I assume to fend off possible tremolo ticking)
- The resistor R27and capacitor C15 has been moved from the board to V3’s cathode and soldered directly to the chassis
- Capacitor across V3’s plate and cathode added

The amp is otherwise in great shape. The main filter caps still look good (the seller said he’s probably only put about 30 hours of playing on it in all these years – he was the first owner). It’s got two RCA 6V6 GTY power tubes in. I’ll be double-checking the bias after changing the tremolo caps.

I am obviously ignorant, but didn’t realize it used an opto-isolator in the tremolo circuit and don’t really understand that part of it yet. But, I do know that when I turn the speed control all the way down, it’s still not that slow. Also, when I turn the speed up, the tremolo effect kind of disappears for a few seconds when I reach the upper end of the pot and then it comes back, but super insanely fast and almost not even noticeable.

The intensity pot on the trem is also … way too much for my liking and generally just not very smooth. Hopefully switching the first two 10nF caps to 20nF will at least slow it down. I’m sure there’s more I need to learn about how this all works.

The other mod I will probably do while I’ve got it open is the robrob normal channel reverb mod.

Here are a few gut shots…

 

[King Fan]

Cool. I can't comment -- I don't speak PCB, I've never played a Deluxe Reverb, and I'm a luddite when it comes to optical trem. (Tho I know you're probably not the only one who prefers the real version.) But the DR is an iconic amp, and in my forum browsing the DRRI gets less diss (= more love) than most of the other RI amps. No. I'm not going down that vintage vs. RI tunnel -- if nothing else, the speakers are different! I assume your speaker is factory?

Anyway, I'm eager to hear what others say about the DRRI in general and useful mods -- with the idea you're trying to design a reference to build an AB763 version or variant.

 

[joulupukki]

So far, in my very-limited experience with now two Fender PCB tube amps it's not too bad navigating around. I just have to do a lot more cross-referencing the schematic and layout diagram vs. what I'm used to with the hand-wired layout. ...and, of course, be really careful to not destroy the pads on the underside of the PCB when tweaking. But there are some good videos online that explain how to pretty easily do it.

I had three 600V Orange Drop .02uF caps and that worked for both mods. Maybe a little bit unconventional to not just re-use the .02uF already in place for the normal channel reverb mod, but I put the 3 stock caps in a baggie in case it needs to be returned to the original (not sure why anyone would want to do that in a RI).

I think these two mods are a good improvement to an already good amp. The optical trem – yeah, I guess I'm not that much of a fan. It's better with the ability to let it get a bit slower. I only really have my PR to compare against and I think I prefer the reverb in the PR better too, but that could be a number of different things.

It does have the stock speaker. A Jensen C12K which, for this amp, sounds pretty darn good. I think in the clean tone department and obviously power, this DR has my PR beat. The main thing I don't really like is the size and weight. ...and that's why I kinda wanted to see for myself so I can decide what to build – still favoring making a head cab, still undecided on built-in reverb. It's definitely really convenient to have it built-in, and it's authentic sounding, but that just makes the whole thing a bit heavier and complex. 1st-world problems.

Here's a new gut shot...

 

[joulupukki]

I think part of the magic of this amp is the speaker. It seems to have “the sound.” I plugged my Princeton Reverb into that speaker and it sounds nearly identical, even though I’d still give the DR the edge because it plays so smoothly.

Not sure if the reverb tanks on these DRRI amps are the best, but the one in this seems to be extremely sensitive. Sometimes if I turn it up past 5 it develops a weird oscillation. Plus, if I bump the amp almost at all, the reverb tank freaks out with that horrible bump-the-springs sound. It also, when I first turn the standby switch on, has a reverb-tank noise. Just to rule out it could be something else I plugged in my PR’s reverb tank to it and it acts totally good and fine. Soon I’ll open up the DR’s reverb tank bag and just double check everything looks mechanically sound.

 

[echuta13]

Yeah, the Jensen C12K is really a great speaker IMO! I suspect it would be a great complement to any BF styled amp. Haven't played it in anything beyond a Deluxe reverb though.

 

[joulupukki]

Not sure if the reverb tanks on these DRRI amps are the best, but the one in this seems to be extremely sensitive. Sometimes if I turn it up past 5 it develops a weird oscillation. Plus, if I bump the amp almost at all, the reverb tank freaks out with that horrible bump-the-springs sound. It also, when I first turn the standby switch on, has a reverb-tank noise. Just to rule out it could be something else I plugged in my PR’s reverb tank to it and it acts totally good and fine. Soon I’ll open up the DR’s reverb tank bag and just double check everything looks mechanically sound.

In reading Rob's AB763 mods I came across what that .0022uF cap is doing on R28. It's supposed to reduce oscillations and noise from the reverb. I was all excited that I had found this mod ... until I realized from my earlier pictures that this mod has already been done. I'm nearly positive that a better reverb tank would fix the issue. I pulled the old tank out and took a look at it and nothing looked mechanically broken, but it definitely has issues when the knob is turned up too much. If I use an external speaker cab (and the one in the DRRI's disconnected) there's no problem. So I'm thinking it's some kind of mechanical vibration issue between the reverb tank and the combo cab's speaker.

 

[King Fan]

What's

So I'm thinking it's some kind of mechanical vibration issue between the reverb tank and the combo cab's speaker.

What's the isolation like between tank and cab, and the bagging / suspension / cushioning?

 

[joulupukki]

What's


What's the isolation like between tank and cab, and the bagging / suspension / cushioning?

Typical vinyl bag with a piece of cardboard at the bottom of the bag with the tank sitting on top of that and then screwed to the bottom of the cabinet.

 

[King Fan]

Typical vinyl bag with a piece of cardboard at the bottom of the bag with the tank sitting on top of that and then screwed to the bottom of the cabinet.

I shoulda figured. Someone smart should chime in. I *thought* I'd read about cases where the factory isolation, padding, securing were upgraded to decrease vibration problems. No recall of details; I could be wrong.

 

[joulupukki]

I wonder if I were to use a heavily-padded bag and instead of screws, use velcro straps so there's no inkling of solid connection with the screws to the bottom of the chassis? That might do the trick. I did notice with an external speaker cab plugged in that if I really cranked the volume up with the reverb set to max that it was just barely starting to do it ... so it's definitely a mechanical vibration thing going on.

 

[corliss1]

I always ask people if they want to slow down the trem on Fenders when I do a service. You just need to swap one of the 3 caps in the oscillation section from .01 to .02 to slow it down a bit.

 

[joulupukki]

Oh, one thing I do have to point out is how buttery smooth the potentiometers are on this DRRI. WOW! In the three amps I've built so far I've been using CTS pots and after hearing Psionic Audio's comments about them (see his video here at timestamp 34:52) I think I'll be trying Alpha pots next. My amps definitely suffer from the going from 0 to way too loud issue. On this DRRI I can dial in to almost any position. Super nice.