MusicMaster Bass

[M Fowler]

A guy dropped of his Fender MusicMaster Bass combo it has hum problem.

Model CFA7010 with 6AQ5 power tubes and 12AX7 preamp tube.

lead dress around the board and pots shows the hum increases as the HT and CT wires are near the pots. Pull them away it is less but still there. It sounds like filament hum. Tubes are okay.

I am thinking about changing the filament string wiring since right now they have 4&5 grounded. Not my gut shot but is exactly like what I am working on.

Mark

[martin manning]

It's very easy to try a 2x 100R artificial CT referenced to the top of the cathode resistor- just put the two resistors on one of the power tube sockets and lift the existing filament ground (might be at the pilot lamp, though...). The hum is 60 Hz, right? Are the filter caps in the one you have there original?

[M Fowler]

Martin thanks, I replaced the main filter cap (dual 20) already and the pilot light is 120v.

I was thinking as you stated two 100r at first power tube and lift ground but thought surely some one must have worked on these amps before

Mark

[martin manning]

I was thinkin' you could tack the 100R's in and try it out faster than you could type the query, but if the one you have is like the pic it would be a little harder to undo and then restore the chassis ground if needed. I wonder how many of these there are? Made over 10-11 year span, but I've never seen one.

[selloutrr]

it was a rather small production run only a few hundred a year left the factory. They where intended to be student practice amps. Bass amps sold at a rate of less then 1:6 of guitar amps.
I'd assume like most practice amps they probably died a horrific death in the persuit to sound like the latest one hit wonder and got thrown away by parents during a move or spring cleaning instead of repaired.

I've been in a couple both needed new tubes and speakers. One had water damage on the cone from a flooded basement. The other was rocked to hard and gave up. Last I looked you can pick them up for $300-400 in working condition.

[M Fowler]

This young guy in my town has a passion for old tube amps.

He was happy with his Gretsch and Traynor repairs so he brought over this Musicmaster and a Bassman 100 for repairs. The kid has a taste for tube tone.

I don't take out anything that doesn't need to and discuss everything with him before I proceed. Once done I bag everything up and hand it over. It is fun to see these old amps fire up and be played through again.

Moved my oldest son into a house this weekend so maybe this week I can get back to the hum.

Mark

[funkmeblue]

I own this same amp. It was the first amp I fixed. Had a cooked power tube socket. It is now a guitar amp.....no hum problems at all even with the increased gain. I replaced all the electrolytics when I replaced the tube socket.

[M Fowler]

I wonder about T3 if that is the problem.

I can see where this would be a fun practice amp for guitar with the bigger speaker in the cab.