'66/'67 Bassman Mod Suggestions?

Discussion in 'Amps and Cabs [BG]' started by lbwdog, Dec 27, 2007.

  1. OK, so I've had this old chestnut for about 22 years. I don't even remember the details of my aquisition, of it but I think a friend either gave it to me or we traded for something,yada,yada,yada. I do remember him telling me that a previous owner had tried to "Boogieize" it. You can see in the frontal pic that there's a "gain?" pot where an input jack should be on the Normal channel.

    The actual date of the amp is questionable as the tube chart has been eaten up by time,bugs, etc. (it's been sitting untouched in my shed for umpteen years.) but I know it's one of the last blackface series before CBS started applying their "improvements", so I'm thinking '66/'67.

    Anyway, I've decided to make use of the old boy and am trying to decide which way to go with it. BTW, it doesn't have to serve as a bass amp since I already have three great solid state amps, so I'll probably use it as a guitar amp too, but do away with the Boogie feature.

    Option A: Restore to original like specs.
    Option B: Restore as above but with some advanced components and/or modifications to improve upon the original design...for bass
    Option C: Take it even further and incorporate some more radical mods (this is where your ideas will be of help)

    BTW, all electronic work (other than the very simple stuff) will be done by a real tech. I've got enough sense not to get over my head in these things!

    So now the floor is open for discussion folks.....let's hear some ideas....


  2. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    Restore it to spec. You can get plenty of amps with advanced features and so-called "improvements," but they're not making 1960's Blackfaces anymore. I'm restoring a 69 SVT right now and had a couple people try to talk me into replacing the old-fashioned 6146B tubes with more common 6550's, but I wouldn't even consider it because you can always get an SVT with 6550's but you can't get them with 6146B's anymore.

    BTW, you do know that the Bassman is really the head from a Twin Reverb combo with the reverb gone, right? That's why they make such great guitar amps.

    EDIT: Whoops! I meant to say a Super Reverb, not a Twin. Second time I made that mistake today!
  3. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    And please get rid of that silly piece of wood and put on the proper grillcloth!
  4. John Wentzien

    John Wentzien

    Jun 25, 2007
    Elberta, AL
    Artist:TC Electronic RH450 bass system (original test-pilot)
    Original specs!..If it's been sitting a long time it will probably need the capacitors replaced..
  5. I never thought these were very useful for bass, beyond quiet rehearsal level, or maybe recording certain tones. They just don't have the quickness, headroom, output level, anything most modern players expect.

    The one you have would seem to be the linear, surf guitar amp. The earlier brownface version had three gain stages in the bass channel if I recall, and that channel smoked for guitar. I would look at getting it returned to blackface specs if you are looking for a clean guitar amp, or modified to the earlier brownface configuration if you like those overdriven tones and you can find a tech to do that for a reasonable price. It's a nice big chassis for hot rodding, with nice chassis mounted tube sockets and adequate trannies.

    I'd look at what kind of a guitar amp I wanted, and see what your tech can do in that direction. There are many modern bass amps that will outdo anything the old bassman will do!
  6. Johnny Crab

    Johnny Crab HELIX user & BOSE Abuser

    Feb 11, 2004
    From the location of the "boogeyize" pot and my recollection of Bassmans(there's one needing repair now in storage) AND Twins, I would almost bet that the control shown is a dual pot(aka Master Volume) inserted between the preamp stage and the output stage. I did such mods in the 70's and 80's to Twins, Showmans, Marshalls. It allowed you to turn the front gain all the way up and then control how much went to the power amp section.

    For DIY restos, there is a book "Guitar Amplifier Handbook" by Jack Darr(mine is 2nd printing 1973) that is a good reference and has one "Fender Model AB763" , aka Twin, schematic in the back which is VERY close to all early Fender designs. There are also a few websites(some down, some work) with schematics of particular models. Example:

    I'd restore it to Option B but KEEP the "Boogey" control if it is a "Master Volume". Those can be very handy dialing up grit or just more drive without turning the amp up to 9 or 10. I'm sure I'll do that to the one here a couple of years from now when the "empty nest" happens and I've more time.
  7. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    Sorry, but I don't buy that for a second. Maybe a Bassman won't get you as loud as you need to be in a loud band using only stage volume, but doggone if they don't sound amazing live and in the studio by mic'ing a cab.

    Having said that, they ARE guitar amps. But other than using 12AX7's instead of 6SL7's, they're not far off from a B-15, which of course is the greatest low-wattage bass amp ever made.
  8. Right, I could kick myself for selling my '64 Showman head a while back to my keyboard player. It went under with Hurricane Katrina. He asked me if I wanted to swap it for the Bassman but I think I'll pass.

    Actually the wood is stock, the grillcloth is just missing.

    Caps fer sure!

    That's kinda what I'm thinking too.
  9. You know, when I first got this thing, I remember plugging it in to try it but honestly don't even remember much else other than some excessive hum or something. I really haven't touched it since.
    I do like the recording tone of old Bassmans, but not doing much recording anymore. I was on staff at Studio In The Country in Louisiana from the early eightiies into the nineties.
    The last major session I did was with Tony Joe White and an old Fender would've been right on the mark.

    For guitar, I'd really like that old funky overdrive, and I think that's what the Boogie mod was supposed to do but I don't think the mod was done well.
  10. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    I still say restore it to exact Blackface specs. If you want gain and master volume, there are only a million amps on the market that will do it. But again, nobody makes 60's Blackfaces anymore. And while I can dig wanting to restore it to Tweed specs, I find that my Super breaks up very nicely once you get past 7, and it's a Silverface, so I think you'll get that breakup anyway.

    The only Fender amps I've seen benefit monetarily from not modding them to spec are Silverfaces, and that's because they really don't sound as good as Blackfaces. But IMHO, Blackfaces DO sound as good as Tweeds, just an ever-so-slightly different kind of good.

    So Tony Joe White, huh? Gator must've got your granny!
  11. Chomp,Chomp,Chomp.....
  12. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The good news is that it's a pre-CBS Fender, probably '64-'65, so in unaltered clean condition it would be worth a goodly amount. The bad news is that crapped up the way it is it's good for parts and that's about it. If you can find a good tech who can restore it to original that would be best.
  13. I never thought that I would find myself disagreeing with you Bill, but I believe that the "Fender Musical" front plate denotes '65 or later CBS era. I believe the pre-CBS models have the "Fender Electric" front plate. source: http://www.provide.net/~cfh/fender.html
  14. John123z


    Jul 7, 2006
    Hershey, PA
    I was faced with the same problem a few years ago. I choose instead to sell it. Mine was in excellent condition. However, 30+ year old caps need replacing and so did some of the scratchy pots. And personally, old carbon comp resistors are garbage. Some people think carbon comp resistors have a special tone, I agree it's called noise. As an electrical engineer, I knew what needed to be done. The problem is that anything you do to this amp will devalue it in someones eyes. I sold the Bassman and put my efforts into rebuilding and modding my Plush 1060s. In the end I considered it a win win for me.

  15. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    There was a transition period when original blackfaces were produced under the CBS label, prior to the introduction of the silverfaces with modified circuitry. They usually have something on them that says 'CBS' in fine print, on the back and on the tube chart, which I don't see on this one, though my '65 did have that. On close inspection this one says patented 1966 by the lamp. My guess is that the innards are NOS pre-CBS, with a 1966 faceplate. Either way, anything pre-silver face will have the same circuit.
    Not quite. The Bandmaster was similar to the Super, but not exactly the same, though both were 40 watters. The Bassman of this vintage was 50 watts. The main difference was that the Super still had a tube rectifier, while the Bassman and Bandmaster had by this time already switched to solid-state diodes. The chassis of quite a few models were shared, but not necessarily the circuits.
  16. jimbilly


    Apr 19, 2006
    I have a stock '68 Bassman head I use pretty often through an 8x10. It's not very loud, but it sounds very warm and 'vintage-ish', - I have not a/b'd it with my b15n (I should do that). I recently had a mid '70s Twin Reverb head (dual showman box), that was quite a bit louder sounding at 100 watts, a good bass amp too. If you're competing with a drummer of any volume, you'll probably need more power, but those Bassmans are great amps.
  17. A9X

    A9X Inactive

    Dec 27, 2003
    Take it to a tech and get it restored. make sure any changed out parts are returned bagged and tagged (useful if you sell it later).
    It will likely need all the PS caps changed by now.

    Nice guitar amp, or recording bass amp.
  18. GlennW

    GlennW Inactive

    Sep 6, 2006
    That's one of the most favorite amps for guitar players.

    Anything you do will probably decrease the $$ value to someone else.

    I'd sell it as is on ebay starting at $400.
  19. +1 It's been "boogized" enough, time to put it back like it belongs.
  20. John123z


    Jul 7, 2006
    Hershey, PA
    Well if your going to do it, then make sure you do the following;

    1. Replace power cord with a 3 prong grounded cord (safety).
    2. Eliminate the death cap and polarity switch (safety).
    3. Replace all power supply caps and all the 20uf 525 volt filter caps.
    4. Replace bias caps.
    5. Replace all cathode bypass caps.
    6. Replace all the carbon comp 100K plate resistors.
    7. Replace the 1500 ohm and 470 ohm resistors that are soldered directly to the power tube sockets. The heat from the tubes degrades them and makes them candidates for a short.

    And make sure you use new fresh caps, not NOS (new old stock). Old caps are old caps.

    The amp will sound great when your done, but some people won't appreciate the work you've done.