Quick calculation check on this replacement resistor

[gkargreen]

I replaced a selenium rectifier in my 80-T control unit with a diode bridge, the voltage feeding a c-r-c power supply. The voltage drop was 7 volts (25v in and 18v out) across a 15 ohm, 2 watt resistor in the schematic, giving a power dissipation of (7*7)/15 = 3.3 watts! With the new diode bridge its 9 volts (27-18) so that the dissipation should be (9*9)/24 = 3.4 watts. I needed a larger value for the resistor to get the voltage down from 27v to 18v, the voltage is used to power the filaments of a series 12AX7 and 6C4, which equals 18v, just like on the schematic. Going by the schematic value I picked up a 2 watt resistor, hooked it in and then applied power to see that everything was working OK, this was before doing the wattage calculations. What had alerted me to the wattage issue was that the new resistor started heating up and making a smell, touching the resistor it was hot! So the question is, does my calculations seem correct? And if so, as I think they are and the hot resistor seems to confirm, wouldn't the original resistor have been too small, wattage-wise, as the original should have been 3.3 watts? Thanks

 

[gadget73]

Math looks right. I'd swap that for a minimum 7w part.

 

[gkargreen]

Thanks gadget, seemed right to me, just wanted some confirmation.