This is a audio-controlled lamp circuit. This circuit requires low voltage input such as pre-amplifiers, tone control, or general audio line level output. It’s also possible to feed the input with signal from small power amplifier output, or high power amplifier witk low volume level. The characteristic of lamp dimming (incandescent lamp) will look like coming from proportional controller since the switching rate of the TRIAC would be much higher than the lamp dimming response. Here is the schematic diagram of the circuit:
If the lamp won’t go off after the audio signal back down to zero, then try to adjust the potentiometer. You can use filament transformer (usually used for tube), or you can also use small tv-antenna-booster transformer (20v-220V), or other small transformer below 500mA. Don’t worry if you can’t fine transformer with exact primary-secondary ratio, since the potentiometer is there for fine adjustment, and you can always change the input voltage level of the audio input signal.