This gas sensor circuit was found in July 1976 Radio Electronics magazine. The TGS sensor was a common type at the time. Note the power supply to the circuit.
This circuit was found in a 1977 Radio Shack documentation. The unijunction transistor can be...
Other series amplifiers such as the MC3301, MC3401 and LM2900 can be used on this circuit. We...
This circuit offers excellent sound quality for headphones of 150 ohms or more. The circuit was...