I found this MusicMaster Bass amp today

[pchilson]

Originally Posted by Paul in Colorado

Good score! With a little love and a a few tweaks youll have a great amp.

Which flea market was it in? I hit the ones on South College in Fort Collins every month or so, but rarely see any musical gear.

Hi,
I pulled out the receipt. The place is Oldies 'N' Goodies on South College in the flea market strip.

[Scott S]

Originally Posted by pchilson

I've been on the Hoffman Amps page looking at caps. I have found all suitable replacements (I believe) except for C2, C5 and C6. Can you enlighten me on these values please?

Click to enlarge this image

2 uF, 10 uF, and 25 uF.

- Scott

[milocj]

2 uF, 10 uF, and 25 uF.

Probably at 25 or 50 volts. Most Fender bypass caps are rated for 25 volts and it works fine but there are a couple of circuits that see right near 25 volts on one or two of these caps so the 50 volt is a safer bet and doesn't affect anything else. Does your schematic show voltages?

The Sprague can that you mentioned sounds like it was a 20uf and 40uf multi-section can. One terminal is the 20uf connection, one is the 40uf connection, and the last is the common ground. This would probably work well to replace your orangish cardboard capacitor if you hook the 40uf section up to the very first filter stage. I'm not sure if bumping up the value that much would be a problem with the 6AQ5 tubes or not (it isn't with 6V6 or 6L6 tubes) and it usually tightens up the low end a bit at higher volumes.

[pchilson]

Originally Posted by milocj

Probably at 25 or 50 volts. Most Fender bypass caps are rated for 25 volts and it works fine but there are a couple of circuits that see right near 25 volts on one or two of these caps so the 50 volt is a safer bet and doesn't affect anything else. Does your schematic show voltages?

The Sprague can that you mentioned sounds like it was a 20uf and 40uf multi-section can. One terminal is the 20uf connection, one is the 40uf connection, and the last is the common ground. This would probably work well to replace your orangish cardboard capacitor if you hook the 40uf section up to the very first filter stage. I'm not sure if bumping up the value that much would be a problem with the 6AQ5 tubes or not (it isn't with 6V6 or 6L6 tubes) and it usually tightens up the low end a bit at higher volumes.

Well, C2 and C5 are showing 1.22V I don't know about C6 I'm guessing its high voltage 288V there?

Are the two with the arrows the C2 and C5 would you suspect?

[pchilson]

Originally Posted by Scott S

2 uF, 10 uF, and 25 uF.

- Scott

Thanks Scott,
Is uF and MFD the same?

[JOHNNY FOWLER]

short answer on caps, yes it ,s the same

[JOHNNY FOWLER]

also look here https://taweber.powweb.com/store/capord.htm for your caps. worked for me i used 2 20@450 caps for the big cap. flatten out the clamp a little at a time till you can slid both new caps in. works fine

[milocj]

According to this schematic it looks like there are 16 volts on the 25uF cap. It also shows that the 2uF is a 50V cap and the other two are 25V caps. The 50V rating is probably just something that was readily available since it shows the same voltage as the 2uF. Basically anything over 25 volts should work for all three of these. A lot of people will just use 25uF @ 50V caps because they don't cost any extra and it gives a little more safety margin.
http://schematicheaven.com/fenderamp...bass_schem.pdf

[pchilson]

Shoot, sorry milocj. I thought I had posted the schematic earlier in the thread. The version of the amp I have is with 6AQ5 instead of the 6V6s in the schematic you posted.

Thanks JOHNNY FOWLER I will check that link out later on.

Click for a larger version.

[milocj]

I didn't realize that I had the wrong schematic, but the values are likely the same. The picture you posted above shows that the 2uF cap is rated at 50V. I can't make out the other one which I assume is the 10uF.

I went back and looked at the original pictures and I can see 25V written on the cap that is C6 and I'm guessing it is the 25uF (that part is hidden in the picture). I'd probably go to a 50V on that cap but it should also survive fine with a 25V since it has so far.

Whenever you get around to doing the caps remember that these electrolytics are polarized and have to go back in with the positive end in the correct direction.

[pchilson]

Allright then, thanks for all the help and information on this guys.
This weekend I may take a run to the electronics store and see what I can get for the electrolytics.

[zook]

Originally Posted by pchilson

Well, C2 and C5 are showing 1.22V I don't know about C6 I'm guessing its high voltage 288V there?

Are the two with the arrows the C2 and C5 would you suspect?

I wouldn't replace those caps. They likely are fine. If musr replace them, send them to me after you remove them.

Winnie

[pchilson]

Originally Posted by zook

I wouldn't replace those caps. They likely are fine. If musr replace them, send them to me after you remove them.

Winnie

Hmm...lets see, highly prized and sought after caps on the open market... Lets start the bidding at $...

[eddiewagner]

Originally Posted by pchilson

After around three hours I was hearing this hard to describe but it was a kind of a hiss almost like something boiling over kindofa sound. It was not a crackling sound at all. This was random almost like did you hear that? kind of a thing.

that is pretty much the same sound that came out of my pro reverb before i got the tubes changed and some minor repairs done. don´t worry, that can be fixed and then you have a very nice amplifier. i guess it twangs like crazy!

[pchilson]

Originally Posted by milocj

I didn't realize that I had the wrong schematic, but the values are likely the same. The picture you posted above shows that the 2uF cap is rated at 50V. I can't make out the other one which I assume is the 10uF.

I went back and looked at the original pictures and I can see 25V written on the cap that is C6 and I'm guessing it is the 25uF (that part is hidden in the picture). I'd probably go to a 50V on that cap but it should also survive fine with a 25V since it has so far.

Whenever you get around to doing the caps remember that these electrolytics are polarized and have to go back in with the positive end in the correct direction.

Hi Jeff,
Jon has been helping me a bit, knows his stuff he does. I had the chassis open tonight to measure some values for him.

Took this pic while in there. You assumed correctly on that cap.

Click for larger image.

[pchilson]

Hey guys

I'm looking to install a fuse in this amp and wonder what size I should use.
I have been looking at other fender amp schematics and see anywhere from 1 amp to 2 amp to 3 amp fuses. What is appropriate for the mmb?

[milocj]

You're going to want a slo-blo (time delay) fuse. Since this is a low power, two power tube amp I'd go with what the Princeton or Princeton Reverb use which is a 1 amp. Unless it blows constantly (and you know that the amp is working properly) you should be fine with this value. The 2 and 3 amp fuses go up in value as the power of the amps goes up.

Good luck, have fun, and stay safe.

Playing with amps gets kind of addicting, doesn't it?

[pchilson]

Yeah, its addicting alright...damnit...haha
Are the fuse holders what are rated for amp or just the fuse or both?
For the slo-blo, is that just the fuse or is that a function of the fuse holder aswell?

In other words, do I need to match the holder and fuse or just get a holder and size the fuse correctly?

Thanks

Originally Posted by milocj

You're going to want a slo-blo (time delay) fuse. Since this is a low power, two power tube amp I'd go with what the Princeton or Princeton Reverb use which is a 1 amp. Unless it blows constantly (and you know that the amp is working properly) you should be fine with this value. The 2 and 3 amp fuses go up in value as the power of the amps goes up.

Good luck, have fun, and stay safe.

Playing with amps gets kind of addicting, doesn't it?

[meyekel]

I see that you have it on Craigslist already, what's up?

[pchilson]

Not looking to part with it really but everything is for sale at the right price.
Interested?

[milocj]

Fuse holders fit the physical size of the fuse and for the values you'll be using they aren't specific to the amperage of the fuse. A 1 amp Slo-blo will be the same size as a normal 1 amp fuse...they are just built to take a momentary spike (like when turning an amp on) without blowing. They usually have a center inside the glass tube that looks like ceramic with a real fine wire wound around it whereas the normal fuses have just the wire going through them.

I would guess that for your amp you'll just get an in-line type fuse holder and you can wire it to the switch and one lead of your new power cord. You can probably get that and the fuse at Radio Shack, Home Depot, Lowe's, etc or I'm sure whoever you order parts from can hook you up with both.

[pchilson]

Ok, I picked up a Fender style fuse holder with a 1 amp slo-blo fuse.
In the pic the green arrow points to the black wire (hot) from the 3 wire power cord. It connects to a terminal strip. The red arrow points to the black wire that comes from the terminal strip (where the black hot wire is soldered) to the power switch that is part of the volume pot.
Would I wire the fuse in as indicated by the yellow lines?

Click to enlarge the image.

[milocj]

I can't completely tell what's going on there in the picture because of the way the wires are crossing each other. In your schematic it looks like it's a circuit breaker of some sort that has both black wires connecting to one side and both white wires connecting to the other side. In the newer version schematic they show a thermal protector that is in-line with the black wire.

Does your power cord wire attach to one terminal (at the top in your picture) and continue on from that same terminal to the switch or does it connect at the top terminal and come out the bottom near the white wires? You don't want to jumper across that device. It sort of looks like that's what you might have been thinking about doing from your arrows but I can't really tell and it might just be coincidence.

It would probably be most effective to disconnect the power cord hot lead from the first terminal at the top and place your fuse between that end of the wire and that terminal (basically between your green arrow and the terminal). This way the fuse is the first thing that the current flow sees as it enters the amp and it would blow before the current reached anything else, including that circuit breaker/thermal resistor thing if your amp has it. I believe that those reset themselves whereas the fuse would just pop if something was wrong.

[pchilson]

The black (hot) wire from the power cord and the black wire to the switch are connected to the same post on the terminal as if it was one continous wire.