Transformer Tl can be any matching transistor type in the range of 500/500 to 2500/2500 ohms. No connections from the SCR or its components are connected to ground. For safety's sake, keep the 117-V line voltage from the amplifier connectionsâ€” that is the reason for using Tl. To adjust, set potentiometer Rl `off` and adjust the amplifier volume control for a normal listening level.
Then adjust the potentiometer until the lamp starts to throb in step with the beat.