"Panel mount" resistors

[maxhifi]

Looking to replace some flat wire wound resistors in the 50W range, I see there's tons of options for new style finned aluminum panel mount resistors. Is there anything I should be aware of before making such a substitution in vintage equipment? Do these require the chassis to act as a heat sink to achieve their full rating? I have never used this new style of reaistor before. Really I would prefer to stay with the original style but availability and cost may present some issues.

[Chip Chester]

Look up your proposed part on Mouser's site, and click the "data sheet" link. Dive into that, and all will be revealed. A random choice showed that, based on power level selected, the un-heat-sinked (free-air) rating was derated to 20 to 60% of full rating. Only when mounted to a chassis was full rating achieved, and a specific surface area was required to do so. (Note that the percentages I mentioned are not "derated by 20% (so, 80%)" but rather derated TO 20%.)

Each mfg. probably has different stats, so pick one out and click the data sheet link.

Good luck!
Chip