Red Bulbs for retics?!?

[dannybgoode]

I am an M0 radio amateur ( equivalent to an Extra class ham in your neck of the woods) so have a very sound knowledge of electronics.

A rheostat does not control the temperature in the same way a thermostat does as it does not take any account of changes in ambient room temperature-it will apply x watts to the heating device regardless of whether the ambient temp is 0c or 100c.

This can (and does) cause overheating whereas a proper thermostat will compensate accordingly.

Further a rheostat applies constant power to the device being heated whereas a pulse proportional stat sends on/off pulses to the device being heated (hence why they're not desirable on a light emitting bulb) and controls the temperature by varying the length of the on pulses. This is a far more efficient method of temperature control as no electricity is 'wasted' so to speak and is by far the best method of controlling a ceramic element (you are correct in that non pulse thermostats work in a similar manner to a rheostat-indeed they contain a rheostat-but as per my earlier point they compensate for changes to ambient temps).

All thermostats I have ever come across will only fail in the off position and as for hysteresis (I don't need to look it up but thanks for the offer) your rheostat set up taking into account my point about ambient air temps will over a 24 hour period create a far larger temperature than a proper thermostat so is a total non issue.

Yes, a rheostat is better than no temperature control but it is no substitute for a proper thermostat either and to suggest otherwise highlights your lack of knowledge not mine.