[HBR] HBR-11; lessons learned to date

[Tim Shoppa]

KJ4KV writes:
> 3. I've measured dozens of cheap (Radio Shack) carbon film resistors,
> including some with the paint partly burned off.  They generally
> measure within 1-2% of marked value unless the overheating is so
> severe that the carbon itself starts to burn.

I have taken metal film resistors and run them
overpower to the point where the whole resistor body was glowing
bright orange. In the cases where the leads didn't fall off (metal
films did best with the leads not falling off) the resistance was
the same as original. Of course all the enamel coating
was long vaporized.

Folks tell me that this rock-solid stability is why I have
to use carbon compositions in old circuits - because they will
go up in value and act like a fuse to protect other parts (e.g.
transformers). Not really sure I believe it. Fuses are there
to stop fires, not to protect circuit components :-).

Tim N3QE