I received this Music Man HD-130 amplifier with the complaint that it hums.
The four output tubes are 5881WXT. The owner replaced the two main filter
caps himself and said it didn't correct the problem. When I opened the unit
and found one of the yellow wires hanging loose from one of the filter caps,
I soldered it to the other yellow wire which was connected to the filter
cap.

See photos he

http://www.pbase.com/image/57610175.jpg
http://www.pbase.com/image/57610176.jpg
http://www.pbase.com/image/57610312.jpg
http://www.pbase.com/image/57610174.jpg

Now the amp is drawing too much current at idle and I definitely need to
check the wiring to the filter caps. I don't service many tube amps like
this. Does anyone have a schematic of this set? I tried the ernieball.com
website but it's not listed there.

Thanks for your reply.
--
David Farber
David Farber's Service Center
L.A., CA

On Wed, 22 Mar 2006 11:30:35 -0800, "David Farber"
wrote:

I received this Music Man HD-130 amplifier with the complaint that it hums.
The four output tubes are 5881WXT. The owner replaced the two main filter
caps himself and said it didn't correct the problem. When I opened the unit
and found one of the yellow wires hanging loose from one of the filter caps,
I soldered it to the other yellow wire which was connected to the filter
cap.

See photos he

http://www.pbase.com/image/57610175.jpg
http://www.pbase.com/image/57610176.jpg
http://www.pbase.com/image/57610312.jpg
http://www.pbase.com/image/57610174.jpg

Now the amp is drawing too much current at idle and I definitely need to
check the wiring to the filter caps. I don't service many tube amps like
this. Does anyone have a schematic of this set? I tried the ernieball.com
website but it's not listed there.

Thanks for your reply.

Hey David,

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

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.

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

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.

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.

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???

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

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.

On Thu, 23 Mar 2006 10:50:54 -0700, Gilbert Bates
wrote:

On Wed, 22 Mar 2006 11:30:35 -0800, "David Farber"
wrote:

I received this Music Man HD-130 amplifier with the complaint that it hums.
The four output tubes are 5881WXT. The owner replaced the two main filter
caps himself and said it didn't correct the problem. When I opened the unit
and found one of the yellow wires hanging loose from one of the filter caps,
I soldered it to the other yellow wire which was connected to the filter
cap.

See photos he

http://www.pbase.com/image/57610175.jpg
http://www.pbase.com/image/57610176.jpg
http://www.pbase.com/image/57610312.jpg
http://www.pbase.com/image/57610174.jpg

Now the amp is drawing too much current at idle and I definitely need to
check the wiring to the filter caps. I don't service many tube amps like
this. Does anyone have a schematic of this set? I tried the ernieball.com
website but it's not listed there.

Thanks for your reply.

Hey David,

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

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.

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

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.

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.

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???

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

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.


Ok, so this is a transition model to 6L6 that I overlooked.

I use to do some work for a music store in town here. Marshall uses
these Sovteks in like the model 4100, dual high gain reverb head.
Marshall runs them fairly hot, but nothing out of the ordinary. A
shorted 5881 was a common problem that I saw 1-6 months down the road
on a new Marshall amp that uses these tubes. Backing the bias down a
little seemed to take care of the failures.

Sorry, but I'm leery of the Sovtek 5881's and probably wouldn't want
to use them it this voltage and with the drive setup on these amps.
While nothing to rave about, they work reasonably well at more
moderate conditions, but at 700V I'd probably look for something else
to use in this amp.

: 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

"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.....


: 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.


** What asinine crap.

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

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.

No such thing is possible with the tube drive 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.


** Funny how MM provide a bias trim pot.


: 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.


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 !!!

The MM transistor drive scheme was a DISASTER.

Have a look at the Peavey Heritage VTX series.

PV got is right - by using TO3 devices for the job.




......... Phil

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

"Skipp replies"

*** And makes a HUGE ASS of himself !!! ***


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.


** Neither does anyone else " over the internet " - you moron.



: 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.


** Bull**** - to BOTH asinine assertions.

Those TO220s were the simply the CHEAPEST devices MM could find that worked.

Their total demise in normal service was as predictable as night following
day.




: 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.


** WHAT ABSOLUTE BULL**** !!!

There are NO such fusible resistors in any MM amp.

Even if fusible resistors were fitted, the puny TO220s would not be saved.


The key is to put
in the proper type output tubes and not have a high current
short or flash over glitch.


** Asinine crapology !!

Tubes guaranteed never to arc or fail to a high current situation at the end
of their life do not exist in the marketplace.

The intense vibrations in a "combo" amp guarantees that the OPPOSITE
happens.



** 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.


** And when the new tubes are not exactly similar ?

Or the bias components age and drift ??



: : 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...


** No-one does any such thing.

Testing a NEW tube has no bearing on its possible failure, maybe years
later.

YOU are an ignorant, lying TURD.



: The MM transistor drive scheme was a DISASTER.

Only your uninformed opinion Phil.


** YOU are an ignorant, lying TURD.


: 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.


** You are an absolute IDIOT who cannot even read.

The TO3 tube diver devices chosen by PV have way higher current, power and
voltage ratings - for damn good reasons.

Power tubes in guitar amps rattle to bits, burn out and often fail
spectacularly.

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

When an output tube fails to a high current draw, it takes the driver device
with it -
INSTANTLY.

This naturally kills the parallel tube too, in a 4 tube model.

No such thing is possible with tubes driving the outputs.


YOU are just NOT interested in REALITY !!!!


**** OFF !!!!

YOU MICKEY MOUSE IMBECILE !!!





........ Phil

Hi David,

Getting back to square one, let me take a moment to try and
answer your question(s) as asked. First off, the hum is not
good news. The factory supplied tubes were made by Phillips,
GE or Sylvania and were tested for operation at the higher
anode/plate voltage used/supplied by many of the Music Man
Amplifier tube models. So any tube you place into a Music
Man amplifier should be tested for operation at the much higher
anode/plate voltage.

Testing tubes for breakdown at higher anode voltages is called
high-pot testing. It's not normally done by most dealers but should
be requested for tubes installed in amplifiers operated well
above the typical anode voltages found in many/most guitar
amplifiers with similar tubes. A few of the better or "high-end"
tube dealers can and do test tubes before shipping. Some mfgrs
like Groove Tubes make and sell tubes specified and tested for
operation in circuits like the Music Man Amplifiers. I could
also direct you to a web site with much information about making
your own basic high-pot tester.

Otherwise you take a gamble any non high- pottested tubes might
flash over, arc or short when placed into the Music Man Amplifier...
very bad news indeed.

Regarding your yellow wire, the real answer to where it goes is
found by tracing where the other end where it's attached and reversing
the wire function out using the location and the circuit diagram.
Otherwise someone with the exact same amplifer open and visible
might be able to tell you where they think the wire goes.

Excessive current draw could be caused by a number of problems,
so you should use the proper diagram, tools and test equipment
to troubleshoot the circuit through. If you have excessive
final/output tube idle current, something in the bias supply
or cathode drive circuit might be out of whack/failed. Depends
on which chassis version and circuit you have. If the tubes you
have in the amplifier are/were sold as hot or cold range type
units, they might not be able to bias up properly at the anode
voltages found in the Music Man Amplifiers.

Typical faults in the cathode drive hybrid circuit are shorted
transistors, the actual bias pot failed or mis-adjusted... when
you have excessive idle current. If your bias pot is the white
thin-flat-square trim ceramic type pot, they are well known for
being problematic after decades of service. Many people spray a
bit of Caig Labs DeOxit onto/into the pot and the circuit again
works fine. Other people replace the pot when they find it to be
the problem source. The Caig Labs DeOxit Spray will restore some
of the ceramic thin bias pots to regular service, it's just a
question of your trust in using the reconditioned original pot
or replacing it (if found to be the source of the problem).

If the cathode drive transistors are shorted, someone probably caused
an unwanted "glitch" event by putting generic replacement tubes
into the amplifier, which were not able to handle the higher anode/plate
voltage. One or more of the tubes might have flashed over - arced
or shorted. You can test and replace the transistors with a cross
referenced device. Also be sure to measure and check the transistor
emitter lead resistors as they can also open upon tube-glitch events.

There are a number of Music Man Amplifier diagrams on the web. I have
a fair number of them from my Music Man Service days and from Ernie
Ball after they bought out Music Man. If you email me direct, I can
help you find a diagram of an amplifier with the same final/output
section to trouble shoot your amplifier.

Once you get the right type of tubes in your working Music Man
Amplifier, it should last for years of playing, no problama'

cheers,
skipp
skipp025 at yahoo.com

: David Farber wrote:
: I received this Music Man HD-130 amplifier with the complaint that it hums.
: The four output tubes are 5881WXT. The owner replaced the two main filter
: caps himself and said it didn't correct the problem. When I opened the unit
: and found one of the yellow wires hanging loose from one of the filter caps,
: I soldered it to the other yellow wire which was connected to the filter
: cap.

: See photos he

: http://www.pbase.com/image/57610175.jpg
: http://www.pbase.com/image/57610176.jpg
: http://www.pbase.com/image/57610312.jpg
: http://www.pbase.com/image/57610174.jpg

: Now the amp is drawing too much current at idle and I definitely need to
: check the wiring to the filter caps. I don't service many tube amps like
: this. Does anyone have a schematic of this set? I tried the ernieball.com
: website but it's not listed there.

: Thanks for your reply.
: --
: David Farber
: David Farber's Service Center
: L.A., CA