"Panel mount" resistors
 

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.

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