Speaking of eBay

[William Donzelli]

> Not really true.  The manufacturing process and resistor structure
> is fundamentally different.  Film resistors are generally an insulating
> core, with spirals of the resistive stuff (thickness, width, and material
> depend on the resistance of course) around the core.  Then there's a    
> protective coating and marking around the outside.
> 
> There are a few applications where the spiral structure has undesired
> inductive effects.  But then there are different varieties of metal films,
> some specifically low inductance.

If a film resistor is spec'd to work at 600 Volts, and it is having some
problems up there, I would say it's crummy.

> I get the impression that the metal-film manufacturing process has seen
> all the benefits of manufacturing technology over the past few decades,
> while the carbon composition process has had no improvement for like
> fifty years.  Mass-produced 0.1% metal film resistors are cheaper than
> 10% carbon composition units.

Yes, I agree. Carbon comp resistors are pretty much a dead technology.
 
> All resistors drift over time :-).  I will admit that carbon compositions
> are much more drifty with respect to just about everything
> (time, temperature, heat cycling, humidity, phase
> of the moon, etc.)

It is quite common (seen it with my own eyes, too) for a 40 year old
carbon comp resistor to drift over 20 percent, and that even includes the
five percent versions. 

William Donzelli
aw288 at osfn.org