Multipurpose temperature control (CB21368E)

This circuit was found in a 1967 RCA SCR manual. It uses period components that can be replaced with modern equivalents.

Power supply 0 to 20 V (CB22176E)
The output current of this power supply depends on the power transistor and the transformer and...
Increasing the voltage of a fixed regulator (CB8476E)
Found in a 90s Electronic Design, this suggestion to have a higher voltage in a fixed regulator...
Direct Coupling Hearing Aid Amplifier (CB14760E)
We found this circuit in the old Mullard transistor reference manual from 1960. The circuit is...