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Post subject: 1970 Fender Musicmaster Bass Amp Restoration
Posted: Fri Sep 20, 2013 7:37 pm
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I picked up this amp online from a seller who was stumped on fixing it. He thought he had a bad transformer and it turned out to be something different entirely. I removed an extra switch he had in the back and put a fuse holder there instead. I then replaced a blown resistor and the thing turned on! He kind of made a mess of the interior. It is mostly his work.
The chassis straps are reissues and are a little too small. I had to modify the baffle to take a logo. I re-covered it with some 70's Silverface cloth. I had to fix the back panel and still have to re-cover it. He gave me a vintage Jensen C12RL that was blown. I bought a new Jensen C12R. I made the mistake of poking a hole in a 1952 field coil speaker that I was installing in a vintage Gibsonette the other day. It was right after I had it re-coned! The buyer was in Japan. I didn't have the heart do drop the bomb on him. Hopefully that doesn't happen again. This thing will need a new handle too. I even got an NOS faceplate from Angela Instruments. It was the only one they had. I'm waiting on the faceplate and my buddy should have some tolex for the rear. I only have Marshall Elephant right now.

http://www.flickr.com/photos/99856663@N04/9846640095/


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Post subject: Re: 1970 Fender Musicmaster Bass Amp Restoration
Posted: Sat Sep 21, 2013 6:29 pm
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Nice job on the refurb so far! Is this the 6V6 version? Enjoy the amp.

T2

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Post subject: Re: 1970 Fender Musicmaster Bass Amp Restoration
Posted: Sun Sep 22, 2013 1:35 am
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It's actually the 6AQ5A version. I'm super upset because the faceplate I got from Angela has an On/Off switch next to the light which leads me to believe it is for the other model. I've decided to have Mojo make me a custom Blackface plate instead. I know they had those around 1980-82 but mine will be a throwback to the 60s. If someone asks if it is an '81 I'll tell them. It's basically a custom amp anyways with the wiring and such. New speaker too. A lot of guys ask too much $ for these things but I expect to get a decent amount considering the work I've put in.


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Post subject: Re: 1970 Fender Musicmaster Bass Amp Restoration
Posted: Sun Sep 22, 2013 7:28 am
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I never knew Fender used the 6AQ5/EL 90 in any amp. One of the most linear 7-pin mini output tube ever made. Kinda down on power, for a Bass amp, though. Like only 9 watts per tube --- max in Class AB1, push-pull.

Does your amp have four 6AQ5A's in the output section?


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Post subject: Re: 1970 Fender Musicmaster Bass Amp Restoration
Posted: Sun Sep 22, 2013 7:39 am
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BMW2002Ti wrote:
I never knew Fender used the 6AQ5/EL 90 in any amp. One of the most linear 7-pin mini output tube ever made. Kinda down on power, for a Bass amp, though. Like only 9 watts per tube --- max in Class AB1, push-pull.

Does your amp have four 6AQ5A's in the output section?


Beemer...these amps came with only two power tubes, in this case 6AQ5A's and single 12AX7 preamp tube. Not very powerful but you should be able to crank it like a champ with 12 inch speaker and get it to talk. In fact you can slide a champ or vibro champ chassis right into these cabinets! Makes a nice fat type champ.

T2

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Post subject: Re: 1970 Fender Musicmaster Bass Amp Restoration
Posted: Tue Sep 24, 2013 8:03 pm
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BMW2002Ti wrote:
I never knew Fender used the 6AQ5/EL 90 in any amp. One of the most linear 7-pin mini output tube ever made. Kinda down on power, for a Bass amp, though. Like only 9 watts per tube --- max in Class AB1, push-pull.

Does your amp have four 6AQ5A's in the output section?


It's a 15-watt (rated) bass amp, with three tubes -- a pair of output bottles and a single 12AX7 to handle the 1st and 2nd gain stages. A small center-tapped tranny performs the role of a phase inverter. The first editions used the 6AQ5's but premature tube failure caused many complaints (and warranty-claim work orders) so Fender wisely decided to re-design the final drive for 6V6GTA's. The OEM driver was a cheap CTS alnico that seldom lasted more than a year with vigorous play. The amp is better-suited as a low-powered harp amp or a "Roadway Inn rig" for traveling guitarists who need to practice in their motel room.

Arjay

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Post subject: Re: 1970 Fender Musicmaster Bass Amp Restoration
Posted: Wed Sep 25, 2013 1:50 pm
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Arjay, Wow! Interstage coupled transformer. Cathode biasing. 300VDC rated caps in the PS (delivering 290VDC to the plates). I wonder who designed this amp? It has to be one of the most unique for the Fender tube line.


http://www.webphix.com/schematic%20heav ... _schem.pdf


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Post subject: Re: 1970 Fender Musicmaster Bass Amp Restoration
Posted: Wed Sep 25, 2013 4:19 pm
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I'm not sure who designed the architecture but I think Ed Jahns used a center-tapped tranny as a phase inverter for his "opus magnus", the 400PS. Perhaps he also had a hand in the Musicmaster bass amp as well......?

Arjay

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Post subject: Re: 1970 Fender Musicmaster Bass Amp Restoration
Posted: Tue Feb 11, 2014 11:22 pm
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Actually this tube version is bout ten watts the 6v6 version is more like 12 but there is some issues with that. I will post a new thread on it having to do with transformers.


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Post subject: Re: 1970 Fender Musicmaster Bass Amp Restoration
Posted: Tue Feb 25, 2014 4:31 pm
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If it was me I would change the tube sockets to octals and put in 6v6s and give it a cap job and put in heavier PT and OT then put in a really good high DB gain speaker I have a Eminence Tonker in mine. Then you will have an amp that is a good grab and go amp that is loud enough to gig with.


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