[ODPILOT]

    I am done recapping my 53-1750 Radio/Phonograph console. There is a resistor (see photo) which connects between 2 power tubes and it gets HOT. I mean, really hot. I can touch it for about a second, anymore than that, I'm sure I would get a burn. This is the long green ceramic resistor you see in the photo - 270 ohms 7 Watts. What bothers me is that when re-installed in the console, this resistor will be only 1/4 inch from the wood on which the electronics box is mounted - and I'm concerned this is a fire hazard. Anyone come across this?? I was thinking of drilling a 2 inch diameter hole in the wood below where this resistor would be once the box is re attached? Any ideas on this?
Thanks,
Mike

[morzh]

If you can touch it for a second, I guess it well below a combustible material burning temperature.
As long as the heat has a way of escaping it's OK.

As for the hole, remember - the hot air escapes up, not down.

[BrendaAnnD]

That looks like a filament dropping resistor. Those normally run quite hot, but no where near the ignition temperature of wood (or even paper, for that matter). It it were hot enough to even ignite paper, it would tend to melt its own solder connections.

[morzh]

Well, all depends on whether the heat has a way of escaping. You do realize that even a low temp heater if well insulated can deliver enough heat to ignite just about anything.
A good example is when old lampshades were covered with newspapers and would catch fire.

However 7W (and a 7W resistor will not be made to dissipate 7W; it is probably 3-4W) is not 40-70W of an incandescent lightbulb, and thisck wood is not thin paper, and the heat has some way of escaping as the radios were designed with this in mind (well, most of them, I guess).

[Raleigh]

Measure the voltage across the resistor and you can calculate the power (wattage) dissipated. You can use the nominal resistance for the calculation--it's close enough. If you want to be super accurate you can measure the actual resistance after desoldering one or the other lead.

E=IR, so I=E/R, and Power = I squared R. Power should be half of the rated value or less. If you are super concerned about the heat, you could buy a power resistor from Mouser or Allied that bolts to the side of the chassis and uses the chassis metal as a heat sink. It will run cooler than your power resistor, but the metal of the chassis will get a little warm. If you buy one of those, check out the derating specs of the resistor. They will often advise derating at 4 times the rated power or more, so if your resistor dissipates 3 watts, buy a 10 or 15 watt power resistor.

I think that's a better solution than drilling a large hole. But my guess is, Philco engineers did their homework and your resistor, assuming it is not defective or degraded, will be fine.