Music Master Bass Amp Mafia

[Sidney Vicious]

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!

[edgetone]

Nice one, Vicious. Poor man's Deluxe....I love mine.

This one's got the 6v6's. Changed the input to a more standard "Fender" arrangement, i.e. 68K and 1Meg resistors and shorted that .047uF cap out of circuit. Sounded really good with a RI Jensen P12Q but wound up with the C12N due to the fact I noodle with a bass on it occasionally. The alnico couldn't take it, the N does fine. I've since added a 1/4" socket/plug connection for the speaker. Made it easier to hook to diferent speaker cabs and such.

Dan

[Sidney Vicious]

edgetone:

That thing is CLEAN! Thanks for posting.

[edgetone]

She'd been around the block a time or two when I met her....

[ravindave_3600]

Had one - but good such a good offer on it (well over then-current value) I had to sell! Highly recommended little amp.

[Sidney Vicious]

Here is a good legible copy of the MMB amp schematic:

[pchilson]

Here is an original schematic for a '74 6AQ5 version MMB
Kinda wish I still had mine...

[Sidney Vicious]

[quote=pchilson;2130503]Here is an original schematic for a '74 6AQ5 version MMB
Kinda wish I still had mine...

Thanks for that - I had not previously seen a schematic specifically referencing the 6AQ5 version.

[varakeef]

Here's mine lurking in the right upper corner... it's a modded version with EL84's (or 34's... how to remember that?)

[Sidney Vicious]

Nice rig, varakeef. The 6AQ5 model, right?

Aside from the feet and tone knob, any other modifications?

[varakeef]

Originally Posted by Sidney Vicious

Nice rig, varakeef. The 6AQ5 model, right?

Aside from the feet and tone knob, any other modifications?

I think it is 6AQ5, 1974 I guess.

It's modded to use different tubes (EL34/84?) since the ones they normally would use were hard to find here when the mod was excecuted (in the early nineties). They probably still are.

I have no idea what the mod exactly is, I just know what tubes to stick in there.

[Sidney Vicious]

I believe the 6BQ5 is "close" to the el84 and so that is likely the tube it was modded to accept. '74 sounds right. Cool amp.

[pchilson]

Originally Posted by varakeef

It's modded to use different tubes (EL34/84?)

These are very different tubes. I would guess they modded to the EL84.

Originally Posted by varakeef

I just know what tubes to stick in there.

Only one type would fit the socket.

[endzone]

Here's mine. Yeah, I'm in the happy camp with MMB's. They are little tone monsters. I picked up an old '65 Jensen P12R for this one and it really stepped it up. This thing will really grind with a P-90. I found this amp at an old obscure flea market about a year ago for $40.

[varakeef]

Originally Posted by pchilson

These are very different tubes. I would guess they modded to the EL84. Only one type would fit the socket.

Yep... and I have a tube chart glued on the back of the amp where the right type is printed on. So I know but I just can't remember that kind of info by heart. The flaws of human brain.

[pchilson]

I hear ya! Use it or lose it...

[doggy1972]

Heres mine






The pictures are a bit limited I'm afraid. Sounds good with all my guitars. Its all stock except for the tubes. 12AT7 for home use 12AY7 for louder situations

[Sidney Vicious]

Sweet rig, doggy - I'll have to give that tube swap a try - I think I have a 12at7 around here someplace.

[doggy1972]

Thanks Sid. I love this little amp. On the lookout for another 1. I know some ppl will say that the 12at7 is a power tube and shouldnt be used for the pre but, it just sounds the best out of the 12ay5, 5751 Ive tried in there.
A question to those in the know- Are those square CTS speakers Alnico or ceramic?
Just a little curious

Ian

[Sidney Vicious]

Originally Posted by doggy1972

Thanks Sid. I love this little amp. On the lookout for another 1. I know some ppl will say that the 12at7 is a power tube and shouldnt be used for the pre but, it just sounds the best out of the 12ay5, 5751 Ive tried in there.
A question to those in the know- Are those square CTS speakers Alnico or ceramic?Just a little curious

Ian

The square magnet on your amp is ceramic - as I believe was stock on all the MMB amps - although some - Oxfords I believe - have a round ceramic magnet.

[doggy1972]

Thanks for the info Sid. The speaker sounds great for lower level breakup.I put an Eminence legend 125 in there for starters but found that, while that speaker could get good cleans, it wasn't really what this amp was about. Put the stock speaker back in and, the magic breakup returned. I have other amps to give me the clean headroom. This is just a plain old bedroom/recording rocker in the small tweed vain. Thats the way it should stay

[dever]

Duuuudes. I just SO got my socks blown off by a 6v6 MMB I just bought tonight for $200. Stock condition, lots of rust and ragged out grillcloth, but holy smokes, my 5e3 is going to have to step up its act now!

It's still got the 2 prong cord and has some grounding hum (though my house is old and has wiring issues). This one's going to stay with me for a while...

Edit: the cord is 3 wires but the ground prong was either broken off or ????

[Sidney Vicious]

Originally Posted by dever

Duuuudes. I just SO got my socks blown off by a 6v6 MMB I just bought tonight for $200. Stock condition, lots of rust and ragged out grillcloth, but holy smokes, my 5e3 is going to have to step up its act now!

It's still got the 2 prong cord and has some grounding hum (though my house is old and has wiring issues). This one's going to stay with me for a while...

Edit: the cord is 3 wires but the ground prong was either broken off or ????

Installing a three-prong is easy and highly recommended - post a picture of your find - and welcome to the MMB Club.

[dever]

Got back around to cleaning up the amp, inside and out, and doing the Richard Hassebrock mods:
http://members.dslextreme.com/users/...MBassCCmod.pdf
http://members.dslextreme.com/users/...ol-Tonemod.pdf

The tone/vol mod definitely provided a more guitar friendly tone, but I found the sweep of the tone pot doesn't provide much change. Easy and worth doing nonetheless. I don't know how much the coupling cap mod made, but it was simple to execute and easy to reverse if needed. I took a bunch of pics I'll post later today.

I left the stock speaker in, but when I put an old p12n into my 5e3, I'll use that current speaker (a Bedrock) into the MMB to see what sort of tones I get out of it then.

I picked up a 6aq5 version off ebay, on its way in the mail. Will be interesting to a/b these. One thing's for sure, the 6aq5 tubes are much more plentiful and a bunch cheaper than nos 6v6's.

[dever]

The layout pics show the two mods perfored, as well as the fuse I installed.

[Sidney Vicious]

dever - neat work on that tone control job - thanks posting the pic.
Post when you get that 6AQ5 in.

[psychetelec]

So, how do you determine the year of manufacture of one of these? Just got one. I notice some have separate on/off switches, some don't.

[Sidney Vicious]

psychetelec: - nice amp!

One indicator of date of manufacture of your amp is the codes on the transformers - that date will tell you the date the transformer was made - the amp was assembled some months (sometimes even a year!) after the transformer was made.

You can also date it by the serial number stamped into the exterior of the rear of the chassis.

Check this link for understanding transformer dating info: http://www.svvintageamps.com/dating.php

Here is some serial number information: http://www.ggjaguar.com/fendamp5.htm

[psychetelec]

Thanks Sid.
Found "A9 + 5-digits - 1979".
It's in great shape, bought it from a friend who'd bought the Musicmaster Bass/Amp package for his son who then decided he didn't wanna play bass. $150.

[Sidney Vicious]

Originally Posted by psychetelec

Thanks Sid.
Found "A9 + 5-digits - 1979".
It's in great shape, bought it from a friend who'd bought the Musicmaster Bass/Amp package for his son who then decided he didn't wanna play bass. $150.

Steal!

[slanted]

Originally Posted by dever

The layout pics show the two mods perfored, as well as the fuse I installed.

im doing a complete makover on my MMB amp - and im gonna ad a fuse - how many amp should the fuse be?

[Sidney Vicious]

I am not tech savvy but have been told that a 100ma or 200ma sloblo will suffice -

anyone else care to chime in?

as I need to get around to doing a fuse as well.

[psychetelec]

So, I tried bi-amping these two, with the Vox handling the low-end and the Fender the high-end, sounds fantastic. We have another orchestra show coming up in a couple weeks, where I have to have my stage volume low, I'm gonna use this rig.

[SimpleOne]

OK Sid better stand up and be counted!

Have had this honey since early 2009.

Got it at GC of all places.The GC in our town seldom, (never?) has any good, cheap, Silver Face Fender tube amps, until one day, yes...one of the experts there made a comment about the amp needing tubes and made a face when telling me this. I wriggled the tubes and discovered they were very loose, one almost falling out on it's own. He did not know I had been looking for just this amp.(mmmwhahaha)

I asked them to eat the tax and they said "OK". $230 out the door.

After tightening the tube sockets up nice and snug the amp sang nicely. Thanks TDPRI and Billm for the tips.

It's a nicely kept '74 model. Stock but for the speaker. What's not to like? Cheap tubes, and plentiful on the net. Great sound too. Can break up without bleedin' ears too...haha. Oh and here's a '68 Vibro Champ for extra consideration...and yes the thought crossed my mind, VC to MMBcabinet

Forgot to add: The speaker in the MMB is a C12K and the Vibro has a P10R. The Vibro came with the baffle board previously modded for a ten inch speaker. I took the 8 ohm speaker out of the Vibro Champ and put that in the SCXD, which sounds glorious with that speaker. Serendipitous.

There are not a lot of choices for 4 Ohm, 10 inch, speakers for guitar amps. "Vintage Speaker" had the best price. Now if I could find an 4 ohm, 12 inch, speaker I might be tempted to at least temporarily switch chassis here.

Great thread Sid!

[SimpleOne]

Originally Posted by dever

The layout pics show the two mods performed, as well as the fuse I installed.

Nice Dever, that fuse holder looks stock. Nice pics!

Originally Posted by Sidney Vicious

dever - neat work on that tone control job - thanks posting the pic.
Post when you get that 6AQ5 in.

Would that be the "Harvard Mod?"

[SimpleOne]

Originally Posted by edgetone

She'd been around the block a time or two when I met her....

Wow nice clean up on that amp. How did you get the grill cloth so clean and sparkly? Remove and gently cleanse it?

[Sidney Vicious]

Finally got around to installing an in-line fuse in my MMB:



Unsoldered the black power line coming in - it was soldered to the fixture holding the big red cap - and unsoldered the black (very dark purple?) line going to the switch from the same tab the black power line was solder to. Spliced the fuse holder in between the two unsoldered ends.

Thus - power - into fuse - out to switch.

[FrankB]

Speaking of Loose tubes.
I have not used my MMB in a bout a year and a half because the tubes fell out of it.. DOH!
hOW DO YOU TIGHTEN THE TUBE SOCKETS ANYWAY?

[SimpleOne]

Originally Posted by FrankB

Speaking of Loose tubes.
I have not used my MMB in a bout a year and a half because the tubes fell out of it.. DOH!
hOW DO YOU TIGHTEN THE TUBE SOCKETS ANYWAY?

Hey Frank here is a linky...

http://billmaudio.com/wp/?page_id=171

Remember to "discharge" the amp. Not difficult but you MUST have a Digital Multi Meter to check for residual voltage, to make sure the capacitors are all drained of their, sometimes, deadly high voltages.

Don't know how? Start a new thread and you will get some help.

[doggy1972]

Update. Just put a Jensen Mod 12-50 in this amp. Put it in to save the stock speaker. Even though its not fully broken in yet, I have to say WOW!!! These speakers are a great deal and sound real nice. I was thinking about the Mod 12-35 but, went for this as the price is the same and the specs seem very close to the C12q. Antone tried the 12-35?