[R-390] Re: Parts Selection

[Perry Sandeen]

Wrote: There's nothing fundamentally wrong with over-speccing replacements. Some here get really
carried away with it (e.g. putting in 1% resistors everywhere...) There is a certain justification
for doing it once in such a way that it won't have to be done again for another 50 years but
garden-variety mylars would suffice almost all the time.
Whoa!!  Time Out.  I do resemble them there remarks.  

I champion 1% metal film resistor replacement over carbon comps for the following reasons. First
they are decades more stable, have a  far lower noise factor, are smaller than, and are one third
the price of carbon comps.  Also some "A"’s 2.2K resistors are underrated so with metal films you
can double up in the same space or opt for the 3/4 watt rated Vishay series.

The only other viable choice are 5% Carbon Films.  I haven’t used them and they are almost the
same price as metal films.

Baring tube or cap shorts 50 years of operation for metal films is just warm up time.

Now about caps.

IIRC, film caps are made by two methods.  One, the metal conductor is sputtered/applied to the
insulating material so that the "foil" that we are used to isn’t there making for a smaller cap. 
"Orange Drop" types actually have the traditional "foil" so are thicker, larger and cost more.

As for mylar insulated caps they appear to be only available as third-tier parts. I know years ago
they were extremely popular.  They are cheap. Neither Mouser or Digi-Key carry them. That
personally raises a "red flag" regarding quality.

Additional clarification or corrections of my comments welcomed.

Regards,

Perrier



 
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