This manual provides comprehensive circuit diagrams and technical information for the 40T, 41T, and 42T series car radios. This series represents a generation that blended established valve technology with emerging transistor output stages, likely produced during the late 1950s through the 1960s. These vintage units are highly sought after by automotive enthusiasts and restorers for their historical significance and are designed to operate within a vehicle's 12-volt electrical system. This document serves as a critical resource for understanding the intricate electrical circuitry of the 40T/41T/42T models. It includes detailed schematics, component identification, and specific insights into 12-volt H.T. valve stages and transistor output stages. The manual is tailored to assist automotive enthusiasts, vintage radio restorers, and repair technicians in troubleshooting, diagnosing, and performing component-level repairs, thereby enabling effective maintenance and preservation of these classic car radios.