http://www.rfparts.com/tranmatch.html

When an amplifier stage has two or more transistors, it is best to have all
devices of the same gain and output to better equalize power sharing and
d.c. current in each device. Other companies only offer matching of “Beta
Codes� — hardly what matching is really about.

RF Parts Company has developed a testing program to provide the service
technician with Premium Matched RF Power Transistors, having the best
quality and performance. First, we select transistors with the same “Lot
Number� and “d.c. Beta�. (This is where others stop and call the transistors
matched.) Next, we test each transistor's B-E, B-C, and C-E junctions with a
curve tracer to separate out those with “undesirable� junction
characteristics. Only transistors with low Collector-Base leakage (Icbo) are
accepted for further testing. Finally, these “Premium� selected parts are
placed in our RF Test Fixture, one at a time. The test measurement is noted
on each part. Our transistor Power Gain test is measured at about 50-60% of
maximum peak power rating. (Note: different drive power levels are used for
the various transistors, and test numbers only apply for the particular part
number under test.)

We select the best parts for matched sets of 2, 4, 8, 16, etc. The number on
the outside of the envelope is the Power Measurement of each transistor as
discussed above. Use of our selected parts will help assure top performance
and reliability in multi-transistor power amplifiers.

GB
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"bobinphx" wrote in message
news:05CYa.40443$Ne.25582@fed1read03...
To all,
I am working with a DC motor that goes forward and reverse. The motor is
controlled by a heat-sinked and fan cooled bank of 5 mj15003
transistors( 5
each forward and reverse). On occasion the motors build up a high amount
of
copper on the armatures, from the brushes and this causes one of the 5
transistors to heat up and fail. The manual and the manufacture suggest
matched transistors. What is a matched transistor????? I am guessing that
they are tested and all have similar characteristics. But what
characteristics am I looking for?? especially in a DC motor control.

Anyone have an answer for a semi technically literate person???? (i.e., I
know the hot end of the soldering iron, from the cold end and have the
scare
to prove it!!!)

Thanks in advance....

Bob in PHX