Proportional temperature controller (CB21277E)

This circuit is from an Electronic Design from the 90's. The main integrated circuit is uncommon nowadays.

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Speaker Protection (CB17274E)
This circuit protects the speakers in case the amplifiers have problems. With a continuous voltage...
2 transistor radio (CB22272E)
We found this circuit in an American documentation from the 60's. The transistors are made of...
Dialing indicator (CB5995E)
This circuit provides a signal when dialing occurs. The circuit is powered by the telephone line...