I just got a DRRI - what mods can/should be done

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Denny, Jun 14, 2006.


  1. Denny

    Denny Member

    Messages:
    1,781
    Joined:
    Mar 23, 2005
    Location:
    Vermont
    what things can or should be done to make the amp "better"? ("better" - not too subjective huh?) Speaker? Caps? yada-yada?

    D.
     
  2. AL30

    AL30 Member

    Messages:
    2,972
    Joined:
    Jul 20, 2005
    Play it. If you just got it you haven't put it through it's paces yet so how can you know what, if anything, you want to improve. Give it some time - you may like it as is, you may not. But you'll never know if you start swapping parts right away.

    Patience Grasshopper.

    AL
     
  3. Denny

    Denny Member

    Messages:
    1,781
    Joined:
    Mar 23, 2005
    Location:
    Vermont
    I do want to install some new tubes "just to be sure" ;o) does anyone have the instructions as to how to bias the amp? I'm 100% aware of the high voltage thing and am 100% capable of performing the procedure - just haven't done it on a DRRI - I did it on a rivera (but not without instructions). I am also thinking of installing 6L6's and need to know what to re-bias it to for those tubes? Thanks

    d.
     
  4. AL30

    AL30 Member

    Messages:
    2,972
    Joined:
    Jul 20, 2005
    Not sure of your amp. There may be a bias pot already inside your amp to allow to bias a new set of tubes. You'll need to check a schematic.

    Does that amp take 6V6 power tubes? If so you may be in for some work if you're gonna swap in 6L6's. According to a posting on some group somewhere - Kevin O'connor posted this

    "6L6s in 6V6 amps:
    1) If the amp was designed for 4x6V6; you can plug in 2x6L6
    2) If the amp was designed for 2x6V6; you CANNOT install ANY 6L6s
    UNLESS-- you add an auxilliary heater transformer to supplement
    the main winding-- 6V6 heaters draw 450mA each
    6L6 heaters draw 900mA each
    OR-- you have the manufacturer's nod that they say it is okay


    6V6s in 6L6 amps:
    1) If B+ is less than or equal to 450V; okay
    2) If B+ > 450V; NOT okay
    UNLESS-- screen voltage can be reduced to below 400V; preferably
    below 350V
    Regarding transconductance and mu: These parameters are a bit more than
    half for a 6V6 relative to a 6L6 i.e. the 'V' has half the gm of an 'L'.
    This fact means that for identical plate voltage, screen voltage and bias
    voltage, the 'V' will settle to an idle current of about half the value
    of a 6L6. This is borne out in actual use and greatly simplifies the
    "bias option" circuit requirements for amps that are to accomodate both
    types of tube."


    AL
     
  5. Denny

    Denny Member

    Messages:
    1,781
    Joined:
    Mar 23, 2005
    Location:
    Vermont
    Thanks - that's too technicle for me - I'll just keep it stock with 6V6's. Where do I measure the voltages (tube pins) and what should the voltage read. There IS a bias pot inside.

    D.
     
  6. tmac

    tmac Goldmember Gold Supporting Member

    Messages:
    2,146
    Joined:
    Jun 29, 2002
    Location:
    The Swamp (Gainesville, Florida)
    I replaced tubes with JJ 6V6's and 12AX7's and NOS Philips 12AT7's, re-biased to about 20 ma, changed speaker to Weber 12F150, lost the bright cap on the trem/reverb channel. That's really all that needs to be done with this amp IMHO. I changed the tone stack caps to Mallory 150's and didn't really notice any major tonal difference, maybe a bit sweeter with the new caps. The only thing amp guru Gerald Webber recommends is changing power supply filter caps to Sprague but I'm not sure that will change tone in any perceptable manner. Some have mentioned that a new Mercury Mag output transformer is very sweet but I don't know. I have other nice vintage Fenders and like my DRRI a lot with these simple changes. I don't think a handwired board is going to do much soundwise. It may make service easier and you can tweak it easier too.
     
  7. Denny

    Denny Member

    Messages:
    1,781
    Joined:
    Mar 23, 2005
    Location:
    Vermont
    I'd like to clip the treble cap too - where is that on the board? I just lift (or cut) one leg correct?

    D.
     
  8. slider313

    slider313 Silver Supporting Member

    Messages:
    7,230
    Joined:
    Jul 28, 2005
    Location:
    NC
    I'd also agree with tmac on the JJ6V6's only I like them about 25ma. As for preamp tubes I'd try to get a mix of RCA,GE,Westinghouse etc. Stay away from Sylvania/Phillips 12ax7's as I find many to be microphonic. Phillips,GE,RCA,Sylvania,Westinghouse,etc. 12at7's are a good bet. The USA old stock preamp tubes will make a world of differance.
     
  9. tmac

    tmac Goldmember Gold Supporting Member

    Messages:
    2,146
    Joined:
    Jun 29, 2002
    Location:
    The Swamp (Gainesville, Florida)
    It's C10 on the board that holds the pots. I like to just wick up the solder on those two joints and just let it fall into the chassis (and take it out of course). No need to cut the legs or remove the board this way. You just have to be decent with an iron.

    From an old post (not mine) and I don't recommend doing all of these:

    I just finished one these for a friend so I've got some notes on the DeluxeReverb RI. The consensus in my neck of the woods is that these RI's are harshand too bright and although no one has played through all of them, the three orfive I've seen have followed that script. I've got an actual 'mod' that workspretty well on these but first things first. The circuit board that all the pots are mounted to holds the 'bright cap' and afew other goodies. The bright cap is designated C10 on the circuit board and itis 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 valuelike 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 thestock 100K to 82K (if it makes the amp too dark for your taste, try a 91K). Thatwill solve most of your problem. Now if you're a 'modding kind of guy', you could go on from there and makethese additional changes, but this is just between you and me. If the guys on thisforum find out what kind of heresy we've been talking, Leo himself willprobably come back from the grave to spank me with a leather amp handle (ormaybe Bill Paley??). And who knows what they'll do to you; just for eventhinking about it. Of course, it is your amp, it's not point-to-point, they currentlymaking lots more and we won't drill any holes, will we?? Oh well, let's get onwith it! Change the cap C7 from 250pf to 430pf or thereabouts (330pf to 470pf). Somefolks say a silver mica cap is a good idea; it surely isn't a bad idea. Changeboth C8 and C9 to .022uf/400volt. My choice would be a good quality cap(sprague orange drop, mallory) at 600volts. Change R21 (mids resistor) from6.8K 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 havethese amps are playing this mod. Now I'm not so sure that I'd do this to a BFDeluxeR. but it seems to help the circuit board model.
     
  10. Denny

    Denny Member

    Messages:
    1,781
    Joined:
    Mar 23, 2005
    Location:
    Vermont
    THANKS VERY MUCH - where can I get the parts that you mentioned? Me thinks me do it ;o).

    D.
     
  11. Blue Strat

    Blue Strat Member

    Messages:
    29,974
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    Tubes and speakers are the most likely candidates for changes. If you have a gold back Jensen speaker in the amp, those tend to be VERY bright. If you replace the speaker, you may not need to remove the treble cap.

    Check out the tube reviews for DRs and DRRIs on my site http://kcanostubes.com/content/newsletter_details.asp?ArticleID=9#DeluxeRevRI

    Biasing is most easily done with a bias probe. I use a Bias Rite from www.tedweber.com
     
  12. Denny

    Denny Member

    Messages:
    1,781
    Joined:
    Mar 23, 2005
    Location:
    Vermont
  13. tmac

    tmac Goldmember Gold Supporting Member

    Messages:
    2,146
    Joined:
    Jun 29, 2002
    Location:
    The Swamp (Gainesville, Florida)
  14. 1guitarslinger

    1guitarslinger Member

    Messages:
    528
    Joined:
    Feb 26, 2005
    I agree with the members who say start with the speaker and tubes first...and lose the bright cab on the vibe channel. I suggest doing those before any further surgery. IMHO, a Weber 12F150 in a DR is a wonderful thing.

    Paul
     
  15. Guitarfever

    Guitarfever Supporting Member

    Messages:
    11
    Joined:
    Jan 31, 2006
    Location:
    Rogers Minnesota
    I did the full blown modification on my DRRI that Tmac has listed and found in the end it causes the reverb to be VERY overdriven. It also causes the volume not to come on until you hit about 1 1/2 on the volume knob. I now need to back out the mods until I find out what's causing these problems. I used the best components money can buy for this, and I've triple checked my work (I'm a technician with 30+ years of experience). It's really not a lot of work and not very compliciated to do these mods, so I'm guessing the full mod has a design problem. I will post something when I figure it all out, I just have to find the time to get back to it. Has anyone else here successfully done all these mods?

    The mods that make the most difference were the following:

    1. Good tubes! I put in old 1940's Westinghouse 6V6's that I got from
    KCA tubes.
    I am using old Mullard 12AX7's and rectifier tube. Really sweet!
    I bet the new 12AX7 gold pin JJ's would be great.
    I've also fooled around with some old RCA 5751's for lower preamp gain.

    2. I replaced the speaker with a Weber C12N type.

    3. Cut the bright cap.

    These mods will smoothen out the brittle sound of the stock DRRI.
    I wouldn't bother doing much more.
    Oh yea..i use a Weber bias rite meter to do my biasing.
    Setting the bias correctly makes a big difference. Make sure you know what your doing!! If you have no electrical/electronic experience, you will need to read up on biasing. You need to understand all the terms like
    crossover distortion, max dissipation etc.. and what a matched pair of power tubes means.
     
  16. Denny

    Denny Member

    Messages:
    1,781
    Joined:
    Mar 23, 2005
    Location:
    Vermont
    I put in some new EH 6v6's and rebiased the amp. Sounds great. Now.....I went to de-solder the treble (trouble) cap (C10) and it's a little difficult to identify which solder "blobs' are the cap since only the underside of the board is showing and the numbers are on the other side. any hints? also - it has the stock speaker in there (black - no label). I have a new Jensen C12N. which speaker will be better? (I don'l like bright sounding amps). The reason i'm asking is first - I don't want to perform a lot of unnecessary surgery; second - I removed the Jenson from my TopHat because to my ears, in that amp, it sounded a bit bright - I don't want to put it in if that speaker is inherently a bright sounding speaker. Thanks

    Denny
     
  17. Dave C

    Dave C Gold Supporting Member

    Messages:
    1,359
    Joined:
    Jun 10, 2005
    Location:
    Waterford Ct
  18. Denny

    Denny Member

    Messages:
    1,781
    Joined:
    Mar 23, 2005
    Location:
    Vermont
    Does anyone have any advice on the speakers I've here?

    d.
     
  19. Texasamp

    Texasamp Member

    Messages:
    33
    Joined:
    Jun 18, 2006
    Location:
    Houston, Tx
    First off, gut that chassis and Blackface it correctly w/ a fixed bias. Big tone change if you do so. You could install a 1 ohm resistor off the cathodes of each 6V6 to measure Mv, or just bias it like I do, the ole seat of the pants way. DMM set to 200mA DC, Red probe on the CT of the OT on the board and the black probe on pin 3 of your 6V6. Use alligator clips when doing this. High voltage is present. Bias it around or close to 70% static plate dissipation at idle. My 6L6GC are rated at 30 watts, so I bias them close to 21 watts, which is 70% at idle.

    I have turned these DRRI's back to thier original tonal sound as back in the 60's many times for customers. They are in awe with the differance it makes.

    Just a suggestion ...

    Regards,
    Darrell S.
    Texas Amplification
    http://www.texasamp.com
     
  20. donnyjaguar

    donnyjaguar Member

    Messages:
    4,230
    Joined:
    Nov 4, 2005
    Location:
    Canada
    As for modifications, I think you should paint flowers and peace signs on the speaker grille and stencil in some dolphins on the side.

    :) :) :)
     

Share This Page