I don't doubt your '74-75 guess. A couple years ago a mint SVT crossed my workbench, with half a dozen Tung-Sol 6550's, date-coded 1972.
As I recall the Tung-Sol factory was some miles distant from Newark NJ's industrial center, and was located alongside a railroad track a bit north of town, near Nutley or Clifton. Two features: there was a road that crossed the tracks, and the factory building bridged the road. So you could "drive through" the factory, and I remember doing just that as a passenger in my parents' car. Atop the factory, a water tank in the shape of a shoulder tube with Tung-Sol painted on the side. A distant memory from childhood, @ early 60's.
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edit: Piqued by your question I did a little internet search here & there. Apparently TS had several sites in and near Newark. Some were making automobile headlamps. (TS was first to develop dual beam headlights. That's how the company got started.) One fellow said his new '74 car had TS headlights. At another location in East Orange TS was trying to get a toe in the water with transistor-making. And another location in Livingston - the TS Chatham division making heavy duty RF and power tubes as well as Geiger-counter radiation sensing tubes. You can still find very tough 5R4 Chatham rectifiers at reasonable prices (for these days).
I guess things started going seriously downhill 1) transistors taking over and 2) when TS was acquired by Studebaker @ 1966, and Studebaker was on its last legs as a car manufacturer. About that time they turned out a revolutionary sports car, the Avanti, but not too many takers. My uncle Ernie had one, and I got a ride in it (impressive! and so were all of Ernie's cars) but that was about the end of the line for another historical quality marque.