I started watching it in '81. Tom Baker's "Robot."
It was just starting on PBS (specifically Channel 2) and advertised for weeks, during This Old House and Nova.
It was running on Channel 11 (another PBS station,) but it was during the news hour, so we couldn't watch it.
On channel 2, it did something bizarre though for the first couple of years, it would just rewind right back to "Robot," after airing "Invasion of Time." So, I would just eventually watch the Pertwee's on the other channel too, when they rewound. Plus, you could watch entire Pertwee shows on Saturday afternoon,
But one time, they just kept going right into "The Keys of Time" and so on, going right to the last Baker show, before rewinding back to "Robot.". The other channel was airing Davisons by then. It took a few years before they aired the Davisons.
So, that's how juggled the series at first.