We found this circuit in a Philips documentation from 1965. The circuit uses a common LDR sensor and the transistors are general purpose types. TR2 can be a BD135.
This twisted pair exciter circuit uses 80's components. The circuit is from a documentation of the time, but...
This control for bass, midrange, and treble was found in the March 1995 issue of Electronics Now...
The SCR sector of this circuit can be powered by high voltage AC and instead of the LEDs we can...