"François Yves Le Gal" wrote in message
...
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.

Ooops. I hadn't looked at the pictures, and my initial answer is
incomplete...

The pix at http://ck37.image.pbase.com/image/57610176.jpg is very
revealing.

It shows two stickers:
"TRANSITION MDL 2100-130
SET-UP 6L6"
and
"SEE: GB2 150 w
OUTPUT
+ BIAS SUPPLY"

So we can presume that this amp is a mongrel, with a 2100-130 front-end
and
a GB2-150 ouput stage and bias supply.

The GB2 used 6L6GC's, so 5881WXT's are fine replacements.

Use the 2100-130 schematics (link already supplied) for the front-end,
and the GB2-150 schematics (see below) for the output stage as well as the
bias supply

http://www.mif.pg.gda.pl/homepages/tom/files/gb2.gif

Hope this will help.



Hi François,

Thanks for those very helpful links. I was able to measure 52 ohms (out of
circuit) from the red to the yellow wire of the output transformer. That
would not seem to be agreeable with the schematic which puts the red on the
primary side and the yellow on the secondary. Looks like the output
transformer is bad.

Thanks for your reply.

--
David Farber
David Farber's Service Center
L.A., CA