Here is five minutes and 33 seconds of The Brady Bunch Variety Hour, which many people know primarily through the awesome Simpsons parody, and which I know primarily through a crusty old VHS tape that got passed around among my friends in the mid-'90s. (Also on this tape: Matt Parker and Trey Stone's The Spirit of Christmas and all of the acting scenes (but none of the porn) from the XXX parody Foreskin Gump.)
The main thing you need to know about The Brady Bunch Variety Hour is that it required the cast of The Brady Bunch to perform a televised variety show in character. On The Donny and Marie Show, Donny and Marie played Donny and Marie. But on The Brady Bunch Variety Hour, Robert Reed played Mike Brady (who was now the star of a variety show). Susan Olsen played Cindy Brady (who was also now the star of a variety show). You get the point. There is never any explanation given as to how Mike Brady transitioned out of his architecture career to star in a singing-and-dancing extravganza with his adult children. One of these adult children we've never seen before—the legendary Fake Jan, called in to replace Eve Plumb, who was the only person smart enough to say no to this project. (And whaddya know? Fake Jan is one of strongest singers in the bunch!)
Bonus delights: The creepy couples-pairing of the stepbrothers and stepsisters, and the canned applause that greets the songs—songs which are clearly so great that audiences burst into applause even when actors pretending to be the Brady Bunch sing them! Also, at 4:38, it appears Robert Reed (or is it Mike Brady???) has a stroke.