A good radio has to have some sort of cooling device....it gives a nice impression.... here's mine for the JBOT (just a bunch of transistors) amplifier.
I don't ever think that the cooler is going to be needed but it's nice to have one with temperature control. It's a simple instrumentation comparator without hysteresis (it's given by the thermal hysteresis on the transistor and "sensing" diode encapsulation).
The reference diode should be near the sensing diode (but not touching the power transistor) to avoid a compensation circuit has if was the case of being a big difference between the inside and outside of the radio since the transistor capsule is in contact with the air outside of the radio.....complicated...no!
I used 1N4148 diodes instead of a 2n2222 (using collector to base pins) transistor, or any other with metallic case, just because it's cheaper with diodes...
The usual crappy video, schematic is on the beginning for a change:
If you don't have 1% resistor you can try with other values, important is to get around 0v between pin 2 and 3 when both diodes are at the same temperature.
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