The transistors of this circuit found in an English 1980s documentation may be the modern BC548 equivalents. The circuit is battery powered and the earphone must be crystal.
The integrated circuit of this amplifier is not very common today. The output transistors can be...
This circuit is from a1970 documentation. R1 may have 10k and P1 47k. The transistors can be BC558...
This circuit is from a 1977 documentation. It is powered by the power supply of the circuit under...