CT-100 Dropping Power Resistor

[Penthode]

I have started this thread as a separate CT-100 discussion pertaining to the 315/800 ohm resistor mounted via an octal socket on the selenium rectifier frame. It is interesting the octal plug as the designers must have anticipated it would fail in service. That would not be surprising as each resistance is supposed to drop 115 VDC. This means that the 315 ohm section dissipates 41 watts and the 800 ohm section 16 watts.

I tested this evening a 330 ohm 50 watt chassis mount resistor with conveniently available 120vac from a power outlet to see how hot it would get. The resistor manufacturer suggests it should be derated for maximum long term reliability. The temperature curve shows that it can dissipate a full 50 watts up to 175 degrees celcius without derating. Upon applying power I measured the temperature of the resistor with my trusty Harbor Freight measuring gun and found it reached 175 degrees in about 150 seconds at which point I removed the power.

I was hoping I may be able to fit a couple of power resistors in the original can. Obviously the over power dissipation of the chassis mount resistors will prevent this. Another thought is a 100 watt 330 ohm resistor alone could fit the can with the lower dissipating 800 ohm mounted on the chassis near the rectifier.

I have stopped to think this through. I have not been able to find how others have coped with this and I am sure others must have had the same problem.

Any suggestions?