The circuit is from a Radio Electronics magazine from October 1987. The Triac must be equipped with a heatsink and the transistors are general purpose.
When the control level is increased from 0 to 1 (LO to HI), this circuit is activated, which...
This 1950's circuit used one of the first commercial transistors and had two stages for audio...
This amplifier can be powered with voltages from 9 to 14 V providing 7W of maximum power under a 8 ohms...