This circuit is suggested by a 1965 General Electric documentation. The triac must be in accordance with the controlled load.
This circuit can operate in a 100 dB range with signals of up to 100 MHz frequencies. Similar...
This circuit is from a 90s Popular Electronics. It appears elsewhere on this site. Q1 can be any...
Suggested by Siliconix in documentation from the 90s, this amplifier has its gain digitally...