WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
Err,
It will eventually get to the same temperature, you cannot beat Ohms law... It still is dissipating 3.75 watts. A bit more surface area might help, but once enclosed it will still run up to the same temperature.