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Music Master Bass Amp Mafia

Discussion in 'Amp Owners Clubs' started by Sidney Vicious, Nov 7, 2009.

  1. Fenderslinger

    Fenderslinger Tele-Meister

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    Thx! That what I thought.. In to the shop it goes!
     
  2. Fenderslinger

    Fenderslinger Tele-Meister

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    So I just finished dialing in my Musicmaster Bass amp!

    I had my tech add a fuse and a 1/4 speaker jack and change a few wonky caps

    When I got it home I rehoused it in a Peter Mather 1x8" champ cab with a JBL D208 I've had kicking around for a while. It's a super cool "sleeper" silverface champ that goes to "11" now :D

    [​IMG]

    [​IMG]
     
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  3. Little Ricky

    Little Ricky Tele-Holic Silver Supporter

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    Cool setup. I rehoused my 6V6 MM in a 70s Champ cab with an Eminence PA speaker (I think a Beta-8).
    Great for home rehearsal, but tried it at rehearsal last night for the first time (Vol @ max, Tone @ min) and with acoustic guitar and vocals going through the PA and drums, it was just keeping up.
    When I turned up the volume at my Pbass it distorted,which sounded ok on one or two songs, but I got by with the bass volume lowered. Playing classic rock type stuff.
     
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  4. Whatizitman

    Whatizitman Friend of Leo's

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    Can I join????!!! Just picked this early MMB up today. Attic find, looks all original, apart from the plug. I’m not powering it up until I open it up and have a looksee at the power supply and such, make sure it’s properly wired and grounded. I have a circuit limiter just for those special moments. :)

    [​IMG][​IMG][​IMG]
     
  5. Whatizitman

    Whatizitman Friend of Leo's

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    :) 00329

    [​IMG]
     
  6. Whatizitman

    Whatizitman Friend of Leo's

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    Works good. High pitched buzz with some volume. Buzz goes away when turning down guitar volume, but not when touching strings. Pre-amp tube? Hmmm. Definitely gets nice and crunchy.

    Seriously can't find anything blatantly wrong with it circuit-wise. Pots need cleaning. The grill cloth looks horrible, but I have enough from a previous project to redo it. Would like to get the surface rust off the handle and corners, if possible. Baffle nuts are missing on one side. Not sure why. Someone screwed that side from the front with one wood screw. You can see it in the pic. Weird. Tolex needs some regluing inside. Speaker connectors are shot. I'll probably just solder the leads when I get it back together.

    I think I'm gonna tackle the cab and baffle first. Then do just the minimum for safety and playability - fuse, caps, fix plug and make sure cord is properly wired and grounded, death cap, etc... I think the tubes and speaker are in good enough shape as is.

    Not sure yet if I want to keep it after I service and clean it up, or flip it. It's a nice find as it's a first batch model. Pine cab, chrome corners FTW.

    Either way, I will need to spend some time playing it to decide. Oh, such a chore LOL (that's for @blowtorch).

    [​IMG]
     
    Last edited: Oct 16, 2019
  7. brimo109

    brimo109 TDPRI Member

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    You are an idiot.
     
  8. Whatizitman

    Whatizitman Friend of Leo's

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    Uh.. that’s a little harsh.

    Anyway, it turns out Home Depot had a few items I needed, so I decided to put off the cabinet. I put in an in-line fuse, cut out the death cap, and replaced the input cap with a jumper. All worked well, for about a minute. Started getting nasty sounding, and eventually cut out. I could restart it a couple of times. But it’s deader than dead now. At least the fuse didn’t blow. So I got that going for me. Which is nice.

    I did discover that the baffle is particle board, and the screw holes are shot. Which explains the screw in the front. Probably gonna make a new baffle out of ply. Ridiculous that these old low end amps had pine cabs, but particle board baffles that disintegrate over time. My multivox in my avatar was the same way. Just silly.

    [​IMG][​IMG]
     
  9. Whatizitman

    Whatizitman Friend of Leo's

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    Uh oh. Worked intermittently while I tried another speaker. Then not at all. Swapped the output tubes around. No sound. Tried the preamp tube on another amp, determined bad tube. Ok, so tried the good preamp tube in the MMB, and no sound. Then a pop. Then smoke. :(

    Opened it up and can’t see any burn or residue. Caps have no visible signs of failure. But they’re the originals. I’m hoping that’s the only issue. New caps and tubes next.

    Fuse never blew. Not sure if that’s a good or bad thing. I have a 1A slow blow.
     
  10. Whatizitman

    Whatizitman Friend of Leo's

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    OK found either the culprit or the victim. One of the output tubes is burned at plate pin. The socket has burn and/or warping at pin 5. Tube has the same burn smell. The other tube doesn't. Not sure what this all could mean, beyond the obvious of bad tube. I will post some questions in the amp forums.

    [​IMG][​IMG]
     
  11. Railway Ritchie

    Railway Ritchie TDPRI Member

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    Hi, Richard here.
    I have a 1970 MMB and I love it.
    Bought it from a small ampguru, was his personel piece, brought back to stock.
    Except for a Jensen speaker.

    I wonder what a Celestion Ruby will do for her.
    Anybody tried yet?
    I'm also eyeballing a second MMB for sale here, for 500€.


    I wanted to upload small 1,5 minute cellphone vid, but was too large.
     
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  12. Railway Ritchie

    Railway Ritchie TDPRI Member

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    Screenshot_20191106-122949_Facebook.jpg
     
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  13. Whatizitman

    Whatizitman Friend of Leo's

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    Pretty sure my PT is good. Getting 258VAC at both secondaries. Heaters measuring ok. No smoking. Hopefully my hack-in tube socket will hold adequately. Everything else good. Just need caps and tubes, replace 1 or 2 drifted resistors, and will be able to get 'er back up and running. Can't wait to finally get some quality play time soon!
     
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  14. Whatizitman

    Whatizitman Friend of Leo's

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    Woohoo!! New caps and tubes. JJ 12ax7 for pre, and NOS milspec 6005s for output. Everything works!! Actually, the old speaker is bad. I was getting some weird bacon sizzle when playing, and buzz at idle. So I swapped in the C12N from my BJr. Holy hell! This thing rocks. No buzz. Loud and proud!

    [​IMG][​IMG][​IMG]
     
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  15. Whatizitman

    Whatizitman Friend of Leo's

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    Swapped in an old RCA 12xa7. Less harsh than the JJ. Tried it with my mojomojo pedal (hates fender BFs and Marshalls). Viola! Excellent toanz!!

    I’m a happy boy today! [emoji4]

    The MOD 35 is on its way. Hoping it will be similar, just not as loud.
     
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  16. Whatizitman

    Whatizitman Friend of Leo's

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    UPDATE. Been playing my MMB almost everyday. The MOD35 is a little quieter, which is nice. Still have to turn it up a bit to fill out the low end and get crunchy, so I use my drive pedals at low volume. Kinda thin at low volume, but that's how it is with tube amps.

    I do have some vibration and occasional sizzle when cranked. I'm hoping it's just a cold solder on one of the resistors or bypass caps, and not my hacked, er... replaced output tube socket. Not sure how I could mount it more secure without major surgery and/or making a mounting plate. Since I mainly play at low volume, I'm in no hurry to address it. Everything else is great. Score, as far as I'm concerned. Keeper for sure.
     
  17. ruark

    ruark TDPRI Member

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    I'm trying to find a way to make my 6V6 mmb breakup earlier. I read that upping the 15k PI resistor is a way, but I also read this does nothing. Does anyone have any insight into what result upping the 15k resistor would have?

    My latest theory is using 6K6 tubes would get me there. From what I gather nothing would need to be changed for the 6K6 to work safely. My band plays pretty quiet so the volume drop the 6K6s would bring is not an issue. My main worry is blowing a transformer or resistor. Would running 6K6s be safe?

    I already have an inefficient speaker. I've considered an attenuator, but would prefer not to. I have no interest in pedals. My main guitar does not have a pickup I can raise. With all this said I really love the tone my guitar and mmb amp have, but it would be nice to get a little bit more breakup distortion at the volume we normally play at. When I got the amp the caps where all dried up, and the volume was real low, but it had the brownest most beautiful fuzz. I shortly recapped it, removed the deathcap, and added a fuse. It's loud and back to factory spec—I just want a little bit of tweed magic added. Thanks for the expertise in advance.
     
    Last edited: Jan 20, 2020
  18. jonrpick

    jonrpick Friend of Leo's

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    Ruark, have you considered the Tweed tone control mod? It's relatively simple. Just replace the existing tone control circuit with that from a Tweed Fender with a single tone knob.

    I preferred it over the stock tone control, and many others do as well. It's completely reversible.
     
  19. ruark

    ruark TDPRI Member

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    Thanks for the suggestion. I have considered the tone control mod, but I have no issues with the tone control the way it sounds or functions so I haven't explored it further. The 6K6's I ordered should be in tomorrow. I'll post my findings. I've talked with TDPRI member—Rob about options. He suggests a type 3 master volume mod or an attenuator. The only issues I have with a master volume is I really don't want to drill a hole in the amp nor do I want the tone/vibe to change too much. I did drill a hole to add the fuse, but that seems almost stock. I know this is not a high dollar amp, but unless I really love the master volume it would be a scar. I could run wires out the back of the amp to the pot so as to give it a few real world tests to see if it's something I would want permanent. I wonder if it would be an issue with the pot not being grounded to the chassis and just flopping outside the back of the amp. Would the free floating pot be a shock hazard or create a possible short if a leg touched the chassis? I'm assuming it would.

    By the way I did not get an email notice that there was a reply on this page. I see where I subscribe now so should be sooner next time.
     
    Last edited: Jan 23, 2020
  20. B-Waters

    B-Waters TDPRI Member

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    Hi all!

    I have recently acquired a '74 MusicMaster bass amp for my studio (obligatory photo provided!) and have enjoyed reading through this informative thread to learn more about this amp, some great info here. Now from what I understand (and please correct me if I'm wrong), during its production this amp underwent 3 changes in its physical appearance:

    1. The earliest 6AQ5 version that features the flat power light, states 'MUSIC MASTER' as 2 words with a gap, state 'BASS AMP', has the chrome protectors on the bottom corners, and the aluminium skirted knobs with black line indicators instead of the black arrow pointers as found on the later versions.

    2. The later 6AQ5A version that has the rounded/domed power light, now states 'MUSICMASTER BASS' instead of 'MUSIC MASTER BASS AMP', no chrome protectors on the bottom corners, aluminium skirted knobs that now feature the black arrow pointers instead of the black line indicators.

    3. The 6V6 version that features a dedicated on/off switch rather than the on/off switch being combined with the volume knob.

    And in addition to the change from using 6AQ5's to 6V6's, these amps also had a change of speaker with some amps installed with a CTS12 and others an Oxford 126PJ4.

    What I would be keen to know is this; in which year did each of these revisions occur and did the change of speaker coincide directly with the change from 6AQ5's to 6V6's and the dedicated power switch? Judging by the knowledge contributed to this thread already I feel sure that someone here will be able answer these questions for me. Many thanks in advance!
     

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