Music Master Bass Amp Mafia

[kiffer]

The plumbers fixed the right leak, no water dripping into the living room. Guys from the insurance have also been and gone, somewhere along the road someone didn't close a window properly because on Thursday I woke to find a skylight open in the attic and no ***** cat in the house. ***** still missing, not a very merry atmosphere.

Meanwhile I measured the voltages on the filter caps : 291V--285V--249V (vs. nominal 293-287-252) which is within 1% so that looks OK. Checking the circuit diagram again I see there's a couple of other voltages I could have measured but most likely they're OK too. I also tightened up the springs of the tube sockets and swapped in the new output glassware, GE 6005/6AQ5W's, and things are already sounding better.

The electrolytics are somewhere in the christmas post, supposedly dispatched on 18 and 19 december, with a bit of luck they should arrive while it's still 2018. While waiting I found this video : which is interesting because the amp does fizzle a bit and my el cheapo DMM does show "something" when set tp its 2000K range - "something" because the figures change faster than I can read them. So maybe I'll change this one too, and the question is of course - stick with 10 nF or go up to 22 or 47?

 

[kiffer]

LOL, ***** was a common term of endearment for a pet cat which is apparently banned from this forum

 

[kiffer]

Meanwhile I measured the voltages on the filter caps : 291V--285V--249V (vs. nominal 293-287-252) which is within 1% so that looks OK. Checking the circuit diagram again I see there's a couple of other voltages I could have measured but most likely they're OK too. I also tightened up the springs of the tube sockets and swapped in the new output glassware, GE 6005/6AQ5W's, and things are already sounding better.

OK, so here's the full list of voltages. First figure is my measurement, in brackets the numbers from mmb_schematic_Medium_.jpg and MMB amp schematic 245V.jpg (in that order).

V1A cathode: 1.19V (1.2,1.23)
V1A anode : 158V (165,164)
V1B cathode: 1.22V (1.2,1.22)
V1B anode : 240V (246,248)
C8 +ve end : 249V (250,252)
C7B +ve end : 285V (287,287)
V2/3 cathodes: 16.8V (16,--)
C7B +ve end : 291V (295,293)

All still looks pretty decent: worst undervoltage is V1A anode at -4.24%, worst overvoltage is V2/3 cathodes at +5%.

After changing the output tubes and cleaning/tightening all sockets that crackling noise has gone and the amp is pretty d--n quiet. Hard to believe it but those electrolytics look like they're still doing a good job after 45 years ...

 

[markeebee]

Little pigs, little pigs, let me in........

Got this a couple of weeks ago, 1972 model. all original (even had the original tubes, and 40-something years of dead spiders inside):

I've recapped it, cleaned out the spiders (very good on toast), bypassed the cap on the input, plopped in some new tubes, changed the speaker to a Private Jack.

Blimey. It's like a Punk Princeton. Strap, on, get in.

Only problem, and it's not something I was expecting.......it's too loud! At rehearsals with a pretty committed drummer (shouldn't they all be committed?) I can crank it to just about 10 o'clock on the dial before it drowns everybody out, but the chunky goodness doesn't start until just after that. So I'm wondering about a Master Volume of some kind. I thought that post-PI might be best, but I'm not sure how that would work with the interstage transformer - I'd be concerned about shorting the secondary. As you can probably tell, I'm straining at the limit of my knowledge here.....anyone got any input, please?

Thanks!

 

[jonrpick]

That interstage transformer is unlikely to saturate/distort in the same way a tube PI would, so I doubt a post-PI MV would buy you anything.

Is yours running 6V6's? If so, with the lower voltages that a MMB runs at, it may be worth considering some of the cheap & plentiful lower-powered 6V6 alternatives out there.

If it's running 6AQ5's, you may have no other option than an attenuator of some sort.

 

[geargasm]

That interstage transformer is unlikely to saturate/distort in the same way a tube PI would, so I doubt a post-PI MV would buy you anything.

Is yours running 6V6's? If so, with the lower voltages that a MMB runs at, it may be worth considering some of the cheap & plentiful lower-powered 6V6 alternatives out there.

If it's running 6AQ5's, you may have no other option than an attenuator of some sort.

I'm running this attenuator:

www.ebay.com/itm/Stamis-Customs-Black-Bird-8-Ohm-65-Watt-Speaker-Attenuator-for-Tube-Amps/322935295884?hash=item4b30718f8c:g:8TsAAOSw3WxaIXz9:rk:11f:0

at home with mine, a 6AQ5, sounds pretty good. I use nothing in rehearsal or live, my band mates are pretty loud! But you are right, these little guys are suprisingly loud for their rated output (12 watts max per Fender Field guide).

 

[Albidextrous]

Hey y’all - just picked up one of these at guitar center - $250 - after tax and delivery. It’s seen better days, but after a tube swap and going into the 2nd instrument input (the first doesn’t work), I’m able to rock it and it sounds pretty darn good with my Jmascis Squier Jazzmaster. I have a friend that’s going to walk me through the process of getting it updated and the such (he suggested this to be a perfect project for a newbie). Any ideas on the grill cloth? Guessing it not original, and neither is the speaker. Any suggestions would be helpful. Also, I’ve read that these aren’t as loud as the 6v6 versions, but someone on this forum suggested changing it to an 18 watt with 6bq5 or 7189’s on the “quest for more volume”, just wondering if anyone went that route and how it went. I would like to get it to a full sound for a baritone guitar, not sure if the 6aq5’s will get me there. Thanks!

 

[Albidextrous]

I got turned on to these by Robbie D of the TDPRI and catnine over on the FDP. Hearing two cool cats singing the praises of such a funky stepchild of a Fender amp got my attention. When I learned how relatively affordable they were/are I really got interested. 12 inches of tube tone for cheap? I'm in.

I have gone through a few of these over the years but recently settled on this early 6AQ5 one:

Bone stock except for the tubes - three RCA's - and, at the moment, a Weber Sig Alnico. Truth be told, for at home play the stock speaker in this thing sounded great for my low-fi hacking. I may end up going back to it.

I have also decided to leave the tone circuit alone on this one - although I will install an in-line fuse soon to protect the trannys.

Step up and show me yours!

P

 

[Albidextrous]

P

This is the one that looks the most like mine! Would love to see more pics, if you have them. No worries if not. I think I found the correct grill cloth on reverb.

 

[soundtronics]

I just bought my first Musicmaster Bass amp from a little old lady on craigslist. It was her ex-husbands and had not been played in 10 years but she said it worked then. It's all original, in great shape, and just dusty. Take it home, plug it in, and WOW. This is it. This is the simplicity I've been looking for. The package I've been looking for. The breakup I've been looking for. Everything WOW. Turn it off. Check out the backside and I have an ice cold 6V6 and a burning hot 6V6. ****. Switch tubes and the problem stays with the socket. Open it up and it was wired wrong at the factory in 1977. The filament/heater voltage was wired to Pin 1 (ground on a 6V6)

instead of Pin 7. ****. I finally find WOW and now I'm going to lose it by fixing this 42 year old problem. So, switch the wires, fire it up, and it ROARS. Beautiful. Erik

 

[Slip Kid]

I bought one off of my guitar teacher a couple months ago. I believe it’s a ‘76. He rescued it from the arts school he teaches at. They were going to throw it away! He had it serviced but decided he didn’t need it. I have been looking for a small low wattage amp for practicing and it more than fits the bill. Plus it fits under my desk.

Mine is missing the original speaker but has something from Univox. It still sounds decent for my use, though. I contacted Jensen for replacement suggestions and they guy who replied told me amp is a secret weapon!

 

[Mothersuperior]

Hello...

Hopefully UPS shows up today w my musicmaster amp.... appears it is the 6v6 version and is in good condition with stock square fender label speaker and what sounds to be the original tubes... at least two prior owners...I don't think any mods have been done...

I would like to join the mafia...I have read all 42 pages of the thread and am super impressed w comments and knowledge within it...

I have a few questions... and bear in mind I am no amp expert and do not play one on tv... . here goes....

I think I am going to throw new 6v6 in that we're essentially new grove tubes from my deluxe... long story short... had an od nose and started with tubes... add well as groove tube 12ax7 from that same amp... add well add Weber signature alcino 12a I have on a shelf...25 w by the looks of it.... does that sound like itwill work well with the amp and if not are there better recommendations....I have a like new dr z 50w ceramic I could throw in it instead...

The death cap.....I want it out... can I just snip the legs off it n call it close enough....I assume not but had to ask.... otherwise I have to take it to a tech n can do so... and would get the other caps and such updated.... my concern is changing what it does to much by doing so... but I have been screenshot the ideas I seen in this thread to have some done like the input cap by pass...

But if it is as good of shape and original add it says....I kinda feel bad for changing to much.... it is intended as a traveler amp and practice amp....

I usually go through my dr z galaxie for most of what I do... and love the amp... but she is pretty heavy. ..

I will post pics once I get my grubby paws on it

Thanks

 

[Mothersuperior]

It showed... strangely ther tube layout says 5ay3 or whatever instead of 2 6v6... had anyone seen that before?... it came w the set of rca tubes as pictured. .. any thoughts to that and the earliest questions would be helpful... thanks

 

[Mothersuperior]

I am hoping someone still goes to this thread.... head anyone seem this rube layout in this amp?....I have only seem the 6v6 and the qtube set ups... when I got it has the 6v6 in that spot but wondering if i should have something different ie the 5y3 in there?..
Thanks

 

[TheOutlaw]

I just bought one of these today before work. I will have to get pictures in the next couple of days when I get a chance. It is a problem child for sure though, at least one tube socket is very loose and it makes a very loud static cracking and popping noise for the first couple of minutes and comes and goes abruptly as you strum chords or hit Bassy notes. I believe the volume is also a lot lower damn it should be, my Blackstar ht1 plugged into a 1x12 seems louder. It is the 6aq5 version and came with rca tubes installed iirc. Would a
16 ohm 12” 1968 Jensen Special Design C12N
be considered an upgrade? Or not even be compatible because of the ohm rating? The amp also doesn't break up nearly as much as I expected when dimed with a fender blacktop Strat. Anyway back to work I will be back in the next couple of days to post pictures and probably look for some advice on how to get it back into shape.

 

[Mothersuperior]

The mafia must be swimming w the fishes.....

 

[TheOutlaw]

Some pics as promised. I also realized I have an Eminence Legend 1258 laying around that I might try later

 

[Fenderslinger]

I just took in a 70's Music Master bass combo amp in a trade and I have a few questions, thanks in advance for any advice or thoughts!!

>It sounds good, but is not nearly as loud as I expected.
I've got a 12 watt Princeton Reverb from the same era that just smokes it in terms of volume. (the volume on 2 on the princeton needs a volume of 5 or 6 on the MMB to sound similar). I had other speakers laying around so I tried a few others in the MMB (one was an EV) and no change.

>My thought in getting this was to place the chassis in a champ cabinet with a vintage JBL D208 8" speaker ive had laying around and have a real sleeper 12 watt "champ".

>The stock MMB 12" cab is in decent shape if anyone in the Los Angeles area might have a champ 8" cab to swap!

 

[rockoski]

Hi guys! I’m voluntary for a new member to your mafia:

I bought my first MMA last week, and it was SOOOO GOOD! So bought another just days later

First one is a -76 model with original speaker (serial A614575). Some work done, fuse ect. Got it for 250€ (ca. $280). Already ordered a Eminence Private Jack 50W speaker for this one.

The second one is a -73 model (serial A05568), with a bigger/better speaker (Fender) and some replacements done. I got the original speaker with me as well! So with a new speaker and some service job done. Unfortunately no fuse installed… Payed 450€ for this one (ca. $500)

Both are with 2 x 6AQ5A tubes (RCA I think, little marking left), don’t think they ever imported that 6V6 model to Finland? Both are super clean, both outside an inside. Both sound soooo good, still quit different tone and feeling and touch.


Also ordered a stereo reverb, EBS Dynaverb, so I can play both in stereo. And put my Mayer Vibe, Octavia, Mad Professor Deep Blue Delay, OCD, or Soul-o-stomp ect. before it on get the sound from both amps. (Got several Fuzzes also, but usually they don’t sound that good with a Fender silverface)

And thank you guys for great inspiration and information!

 

[geargasm]

I just took in a 70's Music Master bass combo amp in a trade and I have a few questions, thanks in advance for any advice or thoughts!!

>It sounds good, but is not nearly as loud as I expected.
I've got a 12 watt Princeton Reverb from the same era that just smokes it in terms of volume. (the volume on 2 on the princeton needs a volume of 5 or 6 on the MMB to sound similar). I had other speakers laying around so I tried a few others in the MMB (one was an EV) and no change.

>My thought in getting this was to place the chassis in a champ cabinet with a vintage JBL D208 8" speaker ive had laying around and have a real sleeper 12 watt "champ".

>The stock MMB 12" cab is in decent shape if anyone in the Los Angeles area might have a champ 8" cab to swap!

There must be something wrong somewhere, tubes or speaker maybe? I have two and they are both loud...and I mean give a Tweed Deluxe a run for it's money loud, not even talking Princeton loud...