Most of thought of the former "independent" General Telephone & Electronics (GTE) as the owner of Sylvania, which made various electronic products. Indeed, it often advertised itself as GTE-Sylvania.
However, they used to be two separate companies until a 1958 merger.
GTE was the largest independent (non Bell System) company with service in parts of 30 states. Sylvania had 45 plants and 20 laboratories in13 states.
General Telephone owned the Automatic Electric company, which made telephone equipment and specialized in the rotary switch.
There is a small article in Billboard magazine which describes it:
(bottom of page 14, Nov 10, 1958)
Also, in 1955 the Stromberg-Carlson company, which manufactured telephone equipment, was merged into General Dynamics.