quality mods for a 59 reissue fender bassman amp

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by crossfiresrt6, Aug 12, 2005.

  1. crossfiresrt6

    crossfiresrt6 Member

    Messages:
    25
    Joined:
    Aug 4, 2005
    Location:
    Edgewood, Maryland
    I own a 59 Fender Bassman re-issue ( 1991 by date code) I was intrested in any quality modifications to help this amp sound closer to an original 59 Bassman. It's tubed with 2 matched Ruby 6L6's / 3 NOS Telefunken 12AX7's in the preamp section and 1 NOS Mullard GZ34 rectifier. I've heard of the Torres modifications but I'm just not sure how close they will bring this amp to my desired goal. I'd appreciate any opinions or information from the quality players here at the gear page.
     
  2. TheAmpNerd

    TheAmpNerd Member

    Messages:
    1,062
    Joined:
    Sep 23, 2004
    Location:
    Tejas


    That sounds like a good start. I have a harp playin' friend
    who plays through one of these and is looking for some
    smoothness and nice tone.

    Right off the top I was thinking the Tung-Sol 5881.
    Perhaps some vintage caps or paper caps, to give
    it that vintage tone. Same with CC or CF resistors
    on the plates, PI, and input mix resistors.

    Anyone else?

    That is the least expensive stuff.

    Otherwise, transformers come to mind, especially
    the output and the choke. I'm always leary of sticking in
    a new power tranny because regulation is NOT the key
    to vintage tone. Better to upgrade the
    output and choke, than the power tranny.

    There are also complete eyelet or turret boards that can be installed to get away from the cheap Fender computer type boards.


    Good luck and let us know what you decide.
     
  3. crossfiresrt6

    crossfiresrt6 Member

    Messages:
    25
    Joined:
    Aug 4, 2005
    Location:
    Edgewood, Maryland
    Thanks, AmpNerd . I appreciate this good advice. Do you have any suugestions on where to get these parts and who manufactures the best one's for the job? ex. Orange drop Cap's/ Hammond Chokes/ Output Tranny's/ Mepco or Sprauge Resistors or Cap's?
    If I go this route I'd really like to get the very best componets available because this amp as it is is very nice and I'm just looking to "tune it" as close to the original's tone as possible without gutting it totally. Your advice sounds very knowledgeable and wise. Thanks very much
    Ed
     
  4. crossfiresrt6

    crossfiresrt6 Member

    Messages:
    25
    Joined:
    Aug 4, 2005
    Location:
    Edgewood, Maryland
  5. outtahear

    outtahear Supporting Member

    Messages:
    1,291
    Joined:
    Jul 1, 2004
    Location:
    Los Angeles CA
    Yup-those are the ones, BUT, I believe the re-issues have much higher plate voltages that might cause issues with (or, "kill") the 5881s. Since you're gonna have to pull that sucker apart to bias it, do you know enough to install a Lg. Zener to drop 40v off the back end?? Tried a 5U4 rectifier??
     
  6. crossfiresrt6

    crossfiresrt6 Member

    Messages:
    25
    Joined:
    Aug 4, 2005
    Location:
    Edgewood, Maryland
    No I am not qualified enough to do what you suggested. Is this something that I should have done when I get the amp rebiased for the 5881's? Is it a necessary procedure or it this something that will enhance the tone of this amp even more than the 5881 TungSol's? How much difference is there in the plate voltage between the 6L6 Ruby's that are in there now and what it is needed to properly drive the 5881's? I have tried the 5U4 rectifier but I prefered the GZ34 Mullard better. It has a sweeter sag to it.
     
  7. VaughnC

    VaughnC Supporting Member

    Messages:
    15,242
    Joined:
    Jan 4, 2002
    Location:
    Pennsylvania
    1) You might want to try reversing the phase of all the speakers. As I understand it, the reissues speaker phase is opposite that of an original Bassman....which means that the speakers in the reissue move backwards instead of foreward on the initial string attack. Some say the difference is night & day while others hear no difference....go figure! It's easily reversable so try it yourself and see what your ears tell you.

    2) The original Bassman used audio taper volume controls whereas the reissue uses linear.

    3) The power supply filtering is different. The input caps on the original Bassman has two 20uf in parallel for 40uf total, whereas the reissue has two 100uf in series for 50uf total. Also, there's extra capacitance on the filter output stage. The original Bassman had a single 8uf cap whereas the reissue has two 22uf caps in parallel for a total of 44uf (big difference there). Some just clip out one of the 22uf caps to get it closer to the original.

    4) The presence control circuit is DC coupled in the original Bassman and AC coupled in the reissue.

    5) The original Bassman had no grid oscillation stopper resistors on the power tubes, wheras the reissue uses a pair of 47 ohmers.

    6) The tone stack is different. The original Bassman used a 56k resistor, 250pf cap, and two .02uf caps. The reissue uses a 100k resistor, 250pf cap, .1uf cap, and .022uf cap.

    7) The original Bassman used a 12AY7 in V1.

    Hope this helps!
     
  8. crossfiresrt6

    crossfiresrt6 Member

    Messages:
    25
    Joined:
    Aug 4, 2005
    Location:
    Edgewood, Maryland
    does this mean that I would be better off having it PTP'd with a Hoffman kit or a Torres kit? Rather than just switching out caps and resistors here and there? I used a 12AY7 in the V1 location but it was a bit too much lower in gain than I liked. I used an Amperx 12AY7 in this spot. How do you go about switching the phase of the speakers? Is it difficult? I was told that a " mercury magnetics"( Ithink that was the manufactuer) output and input tranny would help, is this true? I'm thinking that rather then spend 5 to 8 grand for an original 59 I could get prettyy close to it by just doing the correct mod's to the reissue and spend way less getting there. Many thanks for your help and input!
     
  9. TheAmpNerd

    TheAmpNerd Member

    Messages:
    1,062
    Joined:
    Sep 23, 2004
    Location:
    Tejas
    Holy Smokes VaughnC,

    Very nice indeed.

    I hadn't gotten that deep into it.
    Yeah that heps a lot, as we
    say in Tejas.


    Nice stuff on your TS9s by the way.


    Crossfires,

    PM sent.
     
  10. PacoCasanovas

    PacoCasanovas Member

    Messages:
    593
    Joined:
    Aug 13, 2005
    Location:
    Langenthal, Switzerland
    Hey VaughnC

    thanks a lot! They really use linear volume pots on the reissue bassman??? Sometimes Fender is such as strange company....

    :rolleyes:
     
  11. spikeRI

    spikeRI Supporting Member

    Messages:
    726
    Joined:
    Apr 17, 2002
    Location:
    Tejas
    avoid anything that says Torres.....

    My Bassman RI has a Hoffman Board, MM OT, better speakers and NOS preamp tubes (GE 12AY7) in V1. I've run GE 5881's with a GZ34 rectifier with good results, but preferr KT66's running with a weber 5R4 recifier to bring the plate voltage down.
    The amp sounds way better and is more controllable.......read= not boomy.

    I've tried the backwards speaker thing and noticed no difference.....
     
  12. Sofus

    Sofus Member

    Messages:
    441
    Joined:
    Mar 7, 2002
    What Spike said on Torres. I play a 5F6 style amp, with 3x 5751's in the pre and KT66's in the power section ... with "saggy" rectifiers, and Kendrick Blackframes. The only time I put in a Mullard GZ34 is when I put in the Tung-Sol 5881's, and run the preamp tubes like an original one. I prefer the speakers old style on the RI's and can hear a difference but more so feel it.
     
  13. Calloway

    Calloway Supporting Member

    Messages:
    1,664
    Joined:
    Feb 9, 2005
    Location:
    Austin,TX
    Say what you will about Torres. It may not be true to the original bassman sound, which i understand, but i had the master volume kit put in my old one and it just kicked ass. Everywhere i went people loved the tone, i just ended up moving on to different things.
     
  14. Guinness Lad

    Guinness Lad Silver Supporting Member

    Messages:
    15,338
    Joined:
    Nov 11, 2004
    Location:
    On top a mountain of Chocolate Chips
    I don't want to critize but why not just buy a used Victoria? This amp has everything done to you are trying acheive. If you want to learn about amps which can be cool then what your doing is right on but if are trying duplicate an old tweed amp why not just buy one from somebody who has spent the time and money researching everything about them. All of his components are custom made, even the transformers. By the time you modify everything in your Fender you will have spent way more then if you just bought the Victoria. Does your amp have the plywood cabinet? This goes a long way towards duplicating the sound of the originals. If it is plywood then you will have get a new cabinet made, all this work is not worth it IMHO.
     
  15. Sir EL84

    Sir EL84 Member

    Messages:
    110
    Joined:
    May 5, 2005
    Hi all,

    It should be mentioned that many original Tweed Bassmans came stock with the .02/ .1/ 250pf /100k tone stack. There is currently one on Ebay that shows this if you really look at the chassis. When I had my clone I tried both setups and prefer the sound of the values given in the schematic. The tone stack I mentioned above really scoops the mids out. I guess if you play clean w/ Humbuckers or Bass through one, that could be useful.
    Cheers.
     
  16. jetlag

    jetlag Member

    Messages:
    1,122
    Joined:
    Aug 24, 2004
    The only things I would do to a reissue bassman is add a bias pot, tweak around with tubes and possibly try other speakers. Going past that, I think you're better off selling the amp and buying a used vicky bassman or some other quality clone. As far as tubes, you went a long way with the tele preamps. Once the bias pot is in, I would check the bias on your Ruby 6L6's (whichever ones they are). Make sure you have your Ruby's biased up at least 60 to 65% of max plate watt dissipation. At those levels, if plate voltage was running really high (say, over 465 V)I would try a 5R4G and something like Philips 6L6WGB's with a serious rebias. Maybe TAD shortbottle 6L6WGC's. Then maybe try different speakers - one or two at a time. See if that get's you what you are looking for. All of this stuff is making changes with components that you can keep if you sell the amp (except the bias pot). And the bias pot addition will enhance the amp's saleability. But if you sell the amp, make sure you keep that mullard GZ34 and those tele's!
     
  17. Robboman

    Robboman Member

    Messages:
    182
    Joined:
    Aug 22, 2005
    Location:
    Canada
    Wow, I was about to type the EXACT same thing! Webers made a much bigger improvement than the board kit for me... I installed a board from Martin @ total-tone www.total-tone.com. The board was great, well-priced and better than Hofmann from what I could find. Martin was fantastic, supporting me through all the install (I'm kind of a hack with the electronics). In the end, the board didn't sound a whole lot different than the PCB to my ears (but I needed the bias pot). The Weber speakers though - MAJOR improvement!
     
  18. spikeRI

    spikeRI Supporting Member

    Messages:
    726
    Joined:
    Apr 17, 2002
    Location:
    Tejas
    without changing the OT, you still got a typical boomy modern fender
     
  19. Jeff Flowerday

    Jeff Flowerday Member

    Messages:
    606
    Joined:
    Jan 21, 2003
    Location:
    Calgary, AB Canada
    If your's is a 91' model, the speaker change isn't needed. The Blue Frame Emminence speakers Fender used in the early days are excellent speakers. The current Jensen reissues are crap.

    I've done pretty much every mod under the sun to my bassman, here's what I suggest. All have been mentioned prevously.

    1) Switch the polarity on the speakers.
    2) Get a bias pot installed
    3) Get a 5R4 copper cap rectifier from WeberVST along with a set of Jan Philips 6l6WGB(5881) power tubes (TubeStore) and have the amp biased up properly for them.
    4) Stick a 12AY7 in V1.

    These 4 mods are very unabtrusive and will make a world of a difference overall.

    Beyond these mods you would then look at:

    Hoffman Board
    Mercury Magnetics Output Transformer


    .02
     
  20. spikeRI

    spikeRI Supporting Member

    Messages:
    726
    Joined:
    Apr 17, 2002
    Location:
    Tejas
    mine also has the 5R4 copper cap which brought my plate voltage down to around 410..........
     

Share This Page