Rheostat Source?

[n86121]

The potentiometers ('pots') provide a reference voltage from 0-24 at low current, to the BASE input high of the high current 2N3055 (powe4r supply type) NPN transistors that actually take the load.

If the transistors have fried, any 'ol big juicy NPN transistors will do, as their role is merely amplifying current.

If the pots are jumpy, try spraying corrosion X into the body. Their internal wiper arms and carbon track may be slimed after decades.

If you want to go with rheostats direct to the lighting, check the current. At 24 volts supply, the highest power will be at 12 volts (half way on/off). At 1 amp that is 12 watts heat dissipation, so you would want something rated for 150-200% of that power requirement.

Transistors are easier.