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FWIW, I wasted some of my mis-spent youth working for a manufacturer of
carbon and metal film resistors. Long ago. Carbon film resistors will
run at red heat without damage except to the conformal coating. Metal
film gives greatest stability and its possible to control the
temperature co-efficient. We made zero TC resistors for NASA
contractors. Carbon film is a standard for commercial use, these days
for anything. The main change in manufacturing is the use of laser
cutters to adjust and trim the coatings. We used carbide saws for carbon
and diamond saws for metal film. As a result of the changes in method
film resistors are now very cheap to make. That was the original virtue
of composition resistors but no more.
Composition resistors are made from a slurry of carbon particles in
an insulating carrier. With time, and heat, the number of contacts
between particles becomes less which makes the value go up and also
increases noise. Composition resistors are noisy, the noise being in
excess of the Johnson noise produced by any resistance. Metal film is
the quietest with carbon film being somewhat greater than metal but
still fairly quiet.

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998