The integrated circuit of this amplifier is not very common today. The output transistors can be TIP31 and TIP32 in heat radiators. The circuit is from the 1977 National Semiconductor Audio Handbook.
This is the circuit of a commercial amplifier sold in Japan in the 1960s. The circuit for hearing aid...
This circuit with variable capacitance diode (varicap) is from a publication from the 90s. The...
In the figure we have a simple pulse generator using a unijunction programmable transistor. The...