Trapper John, M. D. was technically not a spinoff from M*A*S*H, which was still on the air at the time, but rather the feature film that spawned that series, said film in turn being an adaptation of a novel.
The concept behind Trapper John, which anchored CBS' Sunday night lineup for 7 seasons (1979-86) was that John McIntyre was now older, wiser, divorced, and chief surgeon at a hospital in San Francisco. Pernell Roberts (ex-Bonanza) was cast as McIntyre, the better to differentiate the character from his younger self, as played by Wayne Rogers in the early years of M*A*S*H.
One thing the two series did have in common was a revolving door with the supporting cast. For example, Mary McCarty, whose character had also previously appeared on M*A*S*H, passed away after production on the first season had ended. The part was not recast, but, rather, another actress, Madge Sinclair, was brought in as a completely new character to fill the void. With McIntyre now essentially the boss/father figure, the focus of youth-obsessed advertisers was on "Gonzo" Gates (Gregory Harrison) and Nurse Gloria "Ripples" Brancusi (Christopher Norris--don't ask why she had a boy's name). As you'll see in the following sample, I think you'd understand why.
Following is the season 2 finale, "Brain Child", with future icon Michael J. Fox as a teenage doctor. Yes, this was a few years before Doogie Howser, M. D..
Unfortunately, no channels on cable systems in the home district carry Trapper John, M. D. at present. Maybe that'll change as the series approaches its 40th anniversary in 2 years.