CheersLike all resistors they only get very hot if you run them at their full rating, bolted to the chassis sounds more than adequate to me if they are for cathode bias.
If they have been replace with 10 watt Arcols and one of those has failed, I would want to check they are not passing too much current. First suspects would be the 2 coupling caps (C6 and C7) for leaking.
Otherwise, Arcols have to be chassis mounted to meet their quoted wattage, if not they usually have about half the rating.
CheersThey should be fine then for the use they have been put to.
The MF A370 power amp used these for the soft start circuit, at mains potential, and they were bolted to the rear of the chassis.... one of the common faults was that the metal body would become live and as the amp is earthed... BANG!!
Just a suggestion, but if you are talking about the EL34 cathode resistors, the originals were 470 ohm,10 watt 'Standees' and were not super reliable. But were conservatively rated as they should have 3 watts dissipation in that circuit. (36 volts across 470 ohms)
If they have been replace with 10 watt Arcols and one of those has failed, I would want to check they are not passing too much current. First suspects would be the 2 coupling caps (C6 and C7) for leaking.
Otherwise, Arcols have to be chassis mounted to meet their quoted wattage, if not they usually have about half the rating.