: Gilbert Bates wrote:
: I'm not going to analyze what you've done already, but I'll give you
: another path for troubleshooting.

I've read some of the posts and will also comment. I'm an original Music
Man Repair Person from way back. If you ask Dan at Ernie Ball Service
about early MM Amplifier questions, he'll probably send you to me. I don't
charge a thing for helping people with questions over the internet.

: The Music Man amps had a tube phase inverter (12AX7) and regular
: output tube biasing, and solid state inverter/driver (no 12AX7) WITH
: TRANSISTOR biasing design in the cathodes of the output tubes.
: Unfortunately, this amp has the transistor drivers as shown in your
: last picture.

I wouldn't say unfortunate... the solid state cathode drive system is very
robust and clean. It takes a lot to kill the early Music Man Amplifiers
and even more to kill the solid state driver version. The advantage of
the solid state system is the output tubes don't need to be rebias when
changing to a same type tube.

: MM amps have very high plate voltages at around 700V+.

Very high and nothing wrong with that. You just have to know to use high
quality tubes, which have been high pot tested for operation.

: These amps use 6CA7/EL34's normally, not 6L6 (5881 Sovtek) types. They
: must be a good quality tube also. Note the voltage rating on both
: types.

Depends on the year and model amplifier. Most of my solid state cathode
driver Music Man Amplifiers came with 6L6 tubes in place. The original
tubes were probably Sylvania, Phillips or GE, which were properly highpot
tested for operation at the higer anode (plate to some of you) voltages.

: I imagine one of the pussy Sovtek 5881wxt's has given out on you under
: the high voltages. If a tube shorts, the transistor in the cathode
: gets the full plate voltage and goes bye-bye on you. This is common on
: the solid state driver MM amps, Google it. So a shorted tube along
: with a shorted transistor may be badly loading your power supply with
: the resultant hum in the speaker.

You will only know what happened by inspection and testing with the proper
tools (multi-meter). I don't like Sovtek Tubes in the Music Man
Amplifers, they tend to flash over at lower plate voltages. I always try
to find NOS Phillips, GE or Sylvania tubes... highpot test them before
placing them into the amplifier. No sense killing the repair cathode
drive circuit a second time.

: Looking at your last picture, It looks like the transistors may have
: been replace at some point before? The screws look a little bunged up
: and I don't think the TIP41C was the original device that came in
: these???

It wasn't... they had special numbers, which cross to current NTE numbers.
I don't have the information right here with me, but you can email me
direct through the web page I post at the bottom and I'll be happy to
tell you what the transistors are and were.

: I have worked on a half dozen MM amps, fortunatley they were the early
: ones with a tube phase inverter :-)

I like the cathode drive (solid state phase inverter) units better, but
that's just me.

: I'd make sure you check the condition of both the output tubes and
: these drive/bias transitors. Look around some, I'm sure you'll find
: some information on this.

You can email me direct from the icons on my web page and I'll try to
answer your questions as time allows.

cheers,
skipp
skipp025 at yahoo.com
www.radiowrench.com/sonic