This circuit of the 70's uses transistors of the time. The circuit can amplify signals from 10 Hz to 100 kHz and modern equivalent components can be used. The circuit is from Ferranti.
This is one of many twin-T oscillator configurations that can be found in this section and on this...
In the MEMs line of the ST available on Mouser Electronics we highlight the MP23AB01DH audio...
Relays specially designed for operation in harsh environments of Phoenix Contact can be purchased...