Passive crossover with automatic tweeter protection?

[allroundFX]

When I was looking for crossover parts I came across a passive crossover with tweeter protection, I know its not a rare thing, you probably know a couple with a fuse or lightbulb as protection.

What intrigued me was the way how the 'automatic tweeter protection' is functioning on the design below:
Link to image

It is the section with the heatsink on the left side. If any one knows how these automatic protection circuits works or have any knowledge of scematics let me know.

[Grant Bunter]

Transistors, with complementary circuitry, can be used for many things.

ie Voltage control, temperature sensing etc etc.

In certain states, (ie to high a voltage, to high a temperature) said transistor can used to stop overload states, or, say, with temperature, shut down in a thermal condition.

Once a bulb is blown, that's it, it has to be replaced, but with a transistor, once the faulting condition is changed (volume turned down reducing voltage, or leading to cooling etc) normal function is restored...