Mystery PCB analysis

I found this circuit board somewhere in the attic and wonder what device it might have belonged to. I probably looked at it before because I notice some markings on the external potentiometers but have no memory of it.

This circuit is way too advanced for me to make sense of at my knowledge level, and I will not continue analysing it any further at this time.

The few things I have been able to deduce:

• Since the top-most plane (labeled 1) is connected to the cooling block of the triac it is most likely to be the ground plane.
• The four diodes close to each other are possibly used as a full-wave rectifier.