This circuit is from a 1980's documentation for telecommunications. The circuit is used in SSB and the diodes must be suitable types for the application. The audio input is low impedance.
We found this circuit in a Popular Electronics of the 90s. The circuit still uses light bulbs, but...
This circuit is from Linear Technology 2005 documentation. The circuit is based on company...
The integrated circuit used in this power supply is no longer very common in power supplies today....