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Please review suggested mods for Deluxe Reverb reissue..

12/18/2005 11:52 PM
Steve A.
Please review suggested mods for Deluxe Reverb reissue..
    Any opinions on these suggested mods for the DRRI posted here in 2000?  
[Mods for the Deluxe Reverb Reissue]  
From the AMPAGE Tech-Talk BBS:  
Name: George Leroy Tirebiter  
Date: 1/XX/00 2:21 AM  
Subject: Re: 65 Deluxe Rev. RI. Too Bright!  
I just finished one these for a friend so I've got some notes on the Deluxe Reverb RI. The consensus in my neck of the woods is that these RI's are harsh and too bright and although no one has played through all of them, the three or five I've seen have followed that script. I've got an actual 'mod' that works pretty well on these but first things first.  
The circuit board that all the pots are mounted to holds the 'bright cap' and a few other goodies. The bright cap is designated C10 on the circuit board and it is found between the #2 jack on the Vibrato channel and the volume control.  
You can take it out (or disconnect 1 leg) but I prefer putting in a smaller value like 43 pf or 39 pf. But what will really help this channel is changing the 'slope' resistor, which is R18 and located around the treble pot. Change it from the stock 100K to 82K (if it makes the amp too dark for your taste, try a 91K). That will solve most of your problem.  
Now if you're a 'modding kind of guy', you could go on from there and make these additional changes, but this is just between you and me. If the guys on this forum find out what kind of heresy we've been talking, Leo himself will probably come back from the grave to spank me with a leather amp handle (or maybe Bill Paley??). And who knows what they'll do to you; just for even thinking about it. Of course, it is your amp, it's not point-to-point, they currently making lots more and we won't drill any holes, will we?? Oh well, let's get on with it!  
Change the cap C7 from 250pf to 430pf or thereabouts (330pf to 470pf). Some folks say a silver mica cap is a good idea; it surely isn't a bad idea. Change both C8 and C9 to .022uf/400volt. My choice would be a good quality cap (sprague orange drop, mallory) at 600volts. Change R21 (mids resistor) from 6.8K to 10K. It is located next to the bass control. On the big circuit board, locate C12, a coupling cap, and change this from the stock .022uf to .047uf.  
Now take that .022uf you just removed and find C25 on this main circuit board. Remove the cap (.001uf) and install that .022uf. Alot of LA players who have these amps are playing this mod. Now I'm not so sure that I'd do this to a BF DeluxeR. but it seems to help the circuit board model.  
If you're after breakup and an overdriven sound then you're done. But if you want to get a slightly cleaner sound or need more headroom for live gigging/bigger rooms, then try this:  
Open up the filter compartment on the underside of the amp and locate the 10K/1watt that feeds the phase inverter (where a 100k resistor and 82k resistor meet). Change THAT 10K resistor to a 2.2K/1watt resistor (this is a Leo/Paley mod).  
You could also install a solid state rectifier. If your amp has as low a B+ voltage as the last RI I saw (405vdc), then this could be a good idea. This  
rectifier brought the B+ up to 420vdc. I would recheck the power tube bias if you go for the SS rect. But only do this SS rect. if you want more clean sound out of your amp.  
Of course, all this stuff is dependent upon what sound you're after, what kind of music you play, what type of guitar you use (and pickups) and what sort of outboard gear you're using. But this will improve these amps and get you started in the right direction.  
Be careful with the circuit board, it is fragile!  
Good luck,  
Steve Ahola
12/19/2005 11:00 AM
Seems like they'd change the character away from a country sound, to a more useful rock sound. I think it's messing with the midrange and you might end up turning the bass knob even lower. Then again the bass knob might have a more useful range than 1-3. Dunno.  
Sometimes I wonder what the Rivera six postion knob mod was. I don't think it was just a selector for paralleling the 250pF with bigger values.
12/21/2005 8:27 AM
"I don't think it was just a selector for paralleling the 250pF with bigger values."  
That's exactly what it was. I don't remember the values, this was back around late 70's - 1980ish when I looked at a couple of them. The amps I looked at had other mods besides that, but that six position mid switch was pretty effective......... but really geared toward distorted sounds.  
12/21/2005 11:55 AM
"That's exactly what it was." it's just progressively bigger caps until it's overly mid-rangey. Simple.
12/19/2005 12:41 PM
Chris/CMW amps

Hi Steve  
Tonestack-changes: pretty nice but more low-midrange, when doing such changes I also change some other caps and resistors.  
PI-input-cap: worser than silverfaces..... some guys may like it but the low-end will be pretty muddy/unclear when dimed.  
Power-supply-R: silverface value, cool for getting more (clean) headroom, slightly less sweet then bf-values but (still) pretty usefull.  
Hope this helps,  
12/19/2005 2:10 PM
Hey Steve,  
The only thing Tirebiter said that I agree with is the description of problem. The mods he suggests don't address it at its core and a couple of them will even make things worse. Note that almost the exact same preamp is used in other amps that sound quite good (i.e. the Vibrolux.)  
The problem is the 415 volts and the cold bias. 6V6s just don't sound their best like that. 6L6s solve the problem but unfortunately the PT isn't really up to it.  
One thing you can do tonewise is to remove the feedback and add a corrective filter. This mainly just removes some of the high end hash but it does so where its being created so its more effective than any messing with the stack. You get to keep the 22W but lose a slight bit of low end tightness. (The amp only has a little feedback, 3dB I think.) If I remember right the best-sounding filter I ended up with was 4.7nF/15K but I could check that if you're interested. Another good thing about this mod is that is easy and reversible and doesn't require messing with either of the boards.  
I'm really surprised you bought it.
12/19/2005 8:57 PM
Steve A.

woodyc said:  
If I remember right the best-sounding filter I ended up with was 4.7nF/15K but I could check that if you're interested.  
    I'd appreciate it if you could check that. A corrective filter is the same as Dr. Z's "conjunctive" filter- from plate to plate on the input into the OT, right? 4.7nF would be the same as 0.0047uF? I believe that needs the full 630vdc rating, but what wattage should the 15k resistor be?  
The problem is the 415 volts and the cold bias. 6V6s just don't sound their best like that.  
    What voltage would you recommend?  
I'm really surprised you bought it.  
    I've wanted one of these amps since 1965, and figured that I could make the reissue sound like a vintage one if I screwed around with it enough. Do you think that part of the problem is with the OT? Is there a replacement that you would recommend?  
--Thanks for your input!  
Steve Ahola  
P.S. I was looking for some nice clean tones, but this amp still sounds constipated to me... just too tight! :( (I replaced the C12K speaker with a reissue P12N, but maybe that has to break in some more...)
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