Strange component with marking SE-B3
That is an SE-B3 error amplifier.

I could not find an example circuit that uses it, or any document with more information than the linked datasheet.

It was most likely used as part of a voltage regulator.

Wikipedia has a section on error amplifiers.

This drawing from the wikipedia article gives a rough idea of how the SE-B3 could be used:



Lacking a better datasheet, I couldn't begin to guess which pin is what on that device.