This circuit was obtained from a 1965 Radio Electronics. The semiconductors used admit modern equivalents. The high voltage coil is an automobile ignition coil.
This circuit uses the LM34 sensor for degrees Fahrenheit and has a scale from 3 to 300º F...
This radio's transistor is powered with the signal's own energy, producing its amplification....
In this circuit the CA3140, an operational amplifier, is used as a comparator with the zener diode...