This circuit was found in the December 1992 Radio Electronis magazine. R2 is an NTC, there is a MOV protector or NTC thermistor. The current depends on the thermistor used.
This circuit, from the 70's, can be assembled with a more modern FET like the BF245. The circuit is...
We found this telephone amplifier in a European publication from the 1980s. The transistor can be...
This is the factory setting (National Semiconductor) of the TDA2006 as an audio amplifier. The...