Need some help with a Fender Musicmaster Bass Amp

[glocker199]

A few months ago I picked up a Fender Musicmaster bass amp for $40 in a newspaper ad. It's an early 70's silverface that was intended as a practice amp for bass. While it's not much good as a bass amp it's a screamin' little guitar amp.

Mine is an early model and very simple. One volume, one tone, two imputs, 15watts, 12" speaker and not much else. It sounds like a double size Champ. The one I have has a 12AX7 preamp tube and two 6AQ5 power tubes.

I play it exclusively at full volume with P90 equipped guitars and sometimes push it with an OD pedal. It sounded good at first, clean, bluesy drive, crunchy growl, but I quickly blew the stock speaker which was light duty at best.

I plan to use this little amp as my full time practice amp and I need to do a little work to it. The first thing will be replacing the broken volume pot and a cap job. I've also heard that there is a bass cut on these that can be easily bypassed. Can anyone give me more details on that?

Also, I'm obviously in need of a speaker. I'm looking for something with good breakup, smooth warm highs, and a punchy bottom. I'm looking at the Jensen MOD 12-35 and C12R as well as the Weber Signature Ceramic. Any ideas on which would work best with this amp?

Any advice would be greatly appreciated.

[olddawg]

Since you seem to be diming the amp for "that" tone anyway. I would be looking around for a 25 watt Celestian green back or knockoff. Also, I'm quite impressed with the newer Eminence speakers. A lot of people like the Union Jack. It's a lot less expensive than a Weber. You can do a lot by tweeking the tone stack or input coupling cap. Can you post a schematic?

[glocker199]

Since you seem to be diming the amp for "that" tone anyway. I would be looking around for a 25 watt Celestian green back or knockoff. Also, I'm quite impressed with the newer Eminence speakers. A lot of people like the Union Jack. It's a lot less expensive than a Weber. You can do a lot by tweeking the tone stack or input coupling cap. Can you post a schematic?

The Weber Signature ceramic I was looking at is a <$50 speaker. Are the green basket Jensen MOD speakers considered a green back clone? At $125 the Celestion is more than I would like to spend for a practice amp speaker.

here is the schematic, except mine is the 6QA5, not the 6V6.

[glocker199]

Fender Musicmaster questions

A few months ago I picked up a Fender Musicmaster bass amp for $40 in a newspaper ad. It's an early 70's silverface that was intended as a practice amp for bass. While it's not much good as a bass amp it's a screamin' little guitar amp.

Mine is an early model and very simple. One volume, one tone, two imputs, 15watts, 12" speaker and not much else. It sounds like a double size Champ. The one I have has a 12AX7 preamp tube and two 6AQ5 power tubes.

I play it exclusively at full volume with P90 equipped guitars and sometimes push it with an OD pedal. It sounded good at first, clean, bluesy drive, crunchy growl, but I quickly blew the stock speaker which was light duty at best.

I plan to use this little amp as my full time practice amp and I need to do a little work to it. The first thing will be replacing the broken volume pot and a cap job. I've also heard that there is a bass cut on these that can be easily bypassed. Can anyone give me more details on that?

Also, I'm obviously in need of a speaker. I'm looking for something with good breakup, smooth warm highs, and a punchy bottom. I'm looking at the Jensen MOD 12-35 and C12R as well as the Weber Signature Ceramic. Any ideas on which would work best with this amp?

Any advice would be greatly appreciated!

I also posted this in the mods section but that might not have been the correct forum.

Here is the schematic.

[hasserl]

Here's a link to a website I started some time ago on these amps with links to a couple of mods for them. musicmaster

I planned to populate the site with more mods, but I've gotten sidetracked with other projects. But do those two mods and use a Weber Alnico Signature 12 and you'll absolutely love the amp. I've got a stable of over a dozen amps, with several vintage Fenders and clones of Fender amps, including 2 MMB amps, and the MMB's will hold their own with any of the other amps. Maybe not in volume, but certainly in tone and responsiveness, touch sensitivity, etc. They are a great little amp. Picking on eup for 40 bucks is one of those great once in a lifetime stories, you did great!!

[glocker199]

Here's a link to a website I started some time ago on these amps with links to a couple of mods for them. musicmaster

I planned to populate the site with more mods, but I've gotten sidetracked with other projects. But do those two mods and use a Weber Alnico Signature 12 and you'll absolutely love the amp. I've got a stable of over a dozen amps, with several vintage Fenders and clones of Fender amps, including 2 MMB amps, and the MMB's will hold their own with any of the other amps. Maybe not in volume, but certainly in tone and responsiveness, touch sensitivity, etc. They are a great little amp. Picking on eup for 40 bucks is one of those great once in a lifetime stories, you did great!!

WOW! That's awesome that you have the detailed directions with pics. Is there any way you can point me to the correct caps at Antique Electronic Supply I'm going to order the vol pot, a spare set of tubes, and an amp handle from them.

Any reason to choose the alnico over a Weber ceramic? Many people have recommended the Webers, but mostly the ceramics.

[hasserl]

Part numbers C-SM500, C-TD0047-630, C-TD022-400 or C-TD022-630.

The alnico mag speaker works better with this type of amp IMO, they provide slight compression when pushed to smooth the distortion. Trust me on this, that speaker is a perfect match for this amp. The sound is awsome, the stuff of legends.

[glocker199]

Part numbers C-SM500, C-TD0047-630, C-TD022-400 or C-TD022-630.

The alnico mag speaker works better with this type of amp IMO, they provide slight compression when pushed to smooth the distortion. Trust me on this, that speaker is a perfect match for this amp. The sound is awsome, the stuff of legends.

Thanks again. I trust you on the speaker, just wondering what the difference was all about. I can't wait to get this thing tweaked up!

[hasserl]

FYI, if the filter caps and cathode bypass caps are original you should probably consider replacing them while you are working on the amp. They are long past their prime and could fail at about any time now.

[glocker199]

I got the Weber Alnico Sig in there and it does sound nice. I guess I was getting quite a bit of speaker breakup with the original before it blew. The weber has very smooth, sweet sounding cleans but the amp doesn't have nearly as much distortion as other Musicmasters I've heard. I'm not looking for a Mesa sound, obviously, just a nice classic overdrive tone.

I've also picked up a Ruby 12AX7 to replace the original tube but it didn't help. I plan on picking up a couple replacement 6AQ5s but they aren't as common so I'll have to order them.

I've found a local amp guy who is going to replace the broken volume pot, check the caps, and do the vol and tone mods. Is there anything else I should have him check as far as the lack of overdrive?

[hasserl]

You know, I have two of these and one of them is much louder than the other and gets a lot dirtier. I'm not sure why, I haven't had a chance to go thru both of them and see what the differences are, as the good one stays at my bandmates place where we practice. One of these days I need to bring it home and open it up and check it out and see where the two differ, other than the good one uses 6AQ5 tubes and the other one uses 6V6's.

You can get more voltage swing out of the PI by increasing the value of the 15k resistor that is in parallel to the phase inverter transformer. You'll have to experiment here, I would go small amounts at a time, try 20k, 25k maybe 30k. The increased voltage swing will drive the power tubes harder and into non-linear operation for increased distortion.

[glocker199]

Another odd thing I noticed when switching out the speaker; There is an original looking Fender tube layout sticker that lists the tubes as a 5Y3GT, 6V6 AND 12AX7.

What the hell?

[edgetone]

First post on this forum. Hello to all.

Not sure if it will help a great deal with your desire for more distortion, but changing the input to a more Fender-like setup will hit the first stage a little bit harder than the stock configuration.

Looking at your schematic, far left, I jumpered the 470uF cap with a piece of wire. This effectively takes it out of the circuit and I believe this is the bass-cut mod you refer to in your original post. Next, I changed the 470K resistor to a 1Meg. This converts the input to standard Fender.

I think you could change the 68K resistors to 20-33K ohms for a hotter signal as well. Somebody correct me if I'm wrong.

I have the 6V6 version and it sounds wonderful after this simple change.

-Edgetone

[czech-one-2]

First post on this forum. Hello to all.

Not sure if it will help a great deal with your desire for more distortion, but changing the input to a more Fender-like setup will hit the first stage a little bit harder than the stock configuration.

Looking at your schematic, far left, I jumpered the 470uF cap with a piece of wire. This effectively takes it out of the circuit and I believe this is the bass-cut mod you refer to in your original post. Next, I changed the 470K resistor to a 1Meg. This converts the input to standard Fender.

I think you could change the 68K resistors to 20-33K ohms for a hotter signal as well. Somebody correct me if I'm wrong.

I have the 6V6 version and it sounds wonderful after this simple change.

-Edgetone

You mean the .0047 cap on the input, jumping that is the 'bass' mod but I left mine in after trying it both ways. Sorry to bump a dinosaur thread....

[Enzo]

Looks like edgetone only made that one post and hasn't been back in seven years.