As to the transistor dummy load, keep in mind that the Hfe (the amplification factor) of a transistor raises when the temperature goes up. That is, assume a transistor with a Hfe of 30. Give a base current of 100 mA and it will draw 3A (transistors are *current* sources, not *voltage* source).
However, as the temperature goes up, Hfe raises to 35. Hence, more collector current and more dissipation, more dissipation is more heat, more heat is more Hfe... thermal runaway.
The easy way is to keep an eye on the meter and adjust the base current. The advanced way is to use a control circuit. Me, being a lazy bum I do keep an eye on the meter. YMMV.
73,
Geert Jan PE1HZG