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I have something to add to this thread. Primetime episodics from that era were usually shot and also post produced on 35mm film. 35mm optical sound has MUCH higher frequency response than the 16mm optical sound you may have heard at your local TV station, or in a classroom. 35mm running speed is nearly three times faster than 16mm, roughly 90 feet per minute, versus only 33 feet per minute for 16mm. Faster media makes reproduction of high frequencies easier. But, that's not all.
Sound post was done using 35mm mag film media, which is audio-only film with a magnetic audio coating mostly across its full width and no photosensitive emulsion. It has sprocket holes along each edge just like 35mm photographic film and also runs at 90 feet per minute. That's 18 inches per second, folks.
Mag film fidelity was incredible for the era, due to wide tracks, higher mass, fast speed, and a very stiff base compared to audio tape. Track skew and wow and flutter were all amazingly low due to mass and dimensional stability.
Mag film was typically used throughout the post process, including the final mix. The visual editing produced a silent "picture master." The audio post produced an "audio-only mag track master." Both final elements were then used to create any 35mm release prints with optical sound that might be needed for network play.
The 35mm optical soundtracks provided to the networks were very good, theatrical in quality, much better than network distribution could support in that era, but sound from the magnetic film is even better.
In most cases, the production studios kept the separate picture and sound masters and those are often used as the sources for what you see and hear today.
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