Found in an 1868 Mullard documentation this circuit has a dynamic range of 10 Hz to 25,000 Hz. Modern equivalent transistors can be used.
August 2017 - STMicroelectronics' new T850 switches with triacs up to 8 A can be obtained from...
This circuit was obtained from the Radio Electronics magazine of August 1962. It is a tandem...
The Texas Instruments OPAx145 Series of Operational Amplifiers is available from Mouser...