Phil Allison wrote:

: "Skipp is a Music Man Amp Technician"
: 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.

: ** How unusual.....

What? that Ernie Ball Service, the current owners of Music Man would refer
you to me or that some would help people for free? I don't charge people
for answering questions. Yeah, there are a few of us out here not trying
to hustle everyone for a buck.

: 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.

: ** What asinine crap.
: Those puny TO220 transistors in MM amp's cathodes *blow up*
: all the time.

Since you know so much about transistors Phil, what's wrong with a
T0-220 transistor package? The original devices were properly rated
for the task and hold up well if the circuit is not abused.

: When an output tube fails high current, it takes the driver
: device with it - INSTANTLY.
: This naturally kills the parallel tube too, in a 4 tube model.

Not really, if you didn't have your head planted, you'd notice
the low value series resistors in the cathode drive circuit, which
can and should be sized to act like fuse links. It was built that way
into some of the original Music Man designs. The key is to put
in the proper type output tubes and not have a high current
short or flash over glitch.

I've had less than 2 Music Man Amplifiers brought in from failed
or flashed over tube issues when they are equiped with the proper
brand and type tubes, which have been properly tested.

: No such thing is possible with the tube drive version.

Tube failure from flash over or shorting is not good news
regardless of which type amplifier they are used. Most hack
techs don't really know about high pot testing tubes so
they do more to damage the amplifier than retube it properly.
You appear to know little about properly testing the replacement
tubes with a high pot.

: The advantage of the solid state system is the output
: tubes don't need to be rebias when changing to a same
: type tube.

: ** Funny how MM provide a bias trim pot.

Not funny, real world. You set it once at the time of mfgr and
get on with your life. If you actually understood the operation
of the circuit, you'd know similar replacement tubes will rebias
at almost the exact same idle current value. It's a really
well done design, which is not turning up in some high end
tube audio designs. Glass Audio/ Audio Amateur Magazine had
a nice write up about it some years back.

: : 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.

: ** Right - EVERY music store and tube dealer has them on offer.
: LOL.

No, few Dealers do so you have to quit being a buffoon and go find
the thinking Tube Dealers that can properly pre-test tubes before
shipping them out. In the US, NDB in Dever (the famous Lord Valve)
and Groove Tubes do pre-test tubes for proper operation. Any good
Tech or Tube Dealer will ensure what they sell works for the application.
Music Man Amplifiers with the much higher anode (plate voltage) are a
special application. Putting an un properly tested tube in any
amplifier is nuts.

: 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.

: ** Is this dude into "double think" or WHAT !!!

Most of the failed Music Man solid state cathode drive failures I've fixed
were caused by people putting the wrong or non highpot tested tubes into
the amplifiers. I've serviced a large number of Music Man Amplifiers
through the years and I own and play through a fair number myself. If you
take care of the amplifier and replace the final tubes with the proper
type, the amplifiers will be trouble free for decades... and have been.

I've got a high pot tester for use with tubes... do you?

: The MM transistor drive scheme was a DISASTER.

Only your uninformed opinion Phil.

: Have a look at the Peavey Heritage VTX series.
: PV got is right - by using TO3 devices for the job.

The TO-220 case style has little to do with the the circuit
style. If you exceed the device ratings they will fail
regardless of the case style. If you operate the Music
Man Solid State phase inverter circuit within it's expected
normal parameters, it will pretty much last for decades
without problems. Many such equiped amplifiers are still
in service without a problem.

Regards,
skipp
www.radiowrench.com/sonic