PHILADELPHIA -- Timing is still everything to Bob Newhart.
You can see it in his appearance tonight night on CBS' "The Big Bang Theory," where he's "Professor Proton," the hilariously bemused childhood idol of Sheldon (Jim Parsons) and Leonard (Johnny Galecki).
"Chuck (Lorre, the show's co-creator) and I have been talking about this for a long time, and we (could) never agree on the show," said Newhart in a recent phone interview.
" I am a big fan of ‘The Big Bang Theory,' and I thought it was extremely well-written and it's done in front of a live audience, and those were the two requirements that I had."
Actually, he had a third -- he wanted to return for at least two more episodes, something he hopes will happen next season.
"It's a little more important than a guest shot," said the former "Newhart" star, who's also appeared in "NCIS" and ABC's "Desperate Housewives," and whose dramatic arc on "ER" scored an Emmy nomination.
He may have made an art form of the well-placed pause -- or stammer -- but the 83-year-old Newhart isn't planning a full stop anytime soon.
"This year, I'll do 20, 25 appearances -- one-night appearances," he said. "I couldn't imagine not doing (it). First of all, it keeps your mind fresh and fertile. And to not have something to look forward to, it would drive me nuts."
He and Don Rickles -- who will be 87 on May 8 -- are "doing an interesting thing in Vegas at the end of May," at an AARP convention, Newhart said.
"Don and I are going to be on stage, not doing our individual acts, but just talking about the trips we've taken and the laughs we've had and then open it up to Q&A," he said. (The two comedians and their wives have long vacationed together.)
"I take a certain enjoyment out of when you play some of these retirement (places). I'm hoping there's a message that, ‘Look, I'm 83, and it's not over, you know. It's strictly in your mind.' "
The former Chicago accountant got his start in comedy recording funny phone calls with a friend at an advertising agency, eventually getting them on local radio.
Newhart did it, he said, "to keep from going crazy," but it also honed his skills for an eventual move into stand-up.
"I was the writer and so I had to write something every day," he said. "And so I had that discipline of coming up with something. And then at one point, Ed (Gallagher), my partner, he got pneumonia, and we were really close to being in violation of our contract (with the radio stations carrying their act). They didn't have to pay us. So we had to do 10 shows in one night. And we snuck into this recording studio and we recorded and that's when we just improvised.
"Then Ed, he got a better job in New York, and so then that's when I started working as a single."
Does he really think that Ed got a better job than he did?
"No," he said.
After Jonathan Winters died April 11, Newhart tweeted, "Jonathan Winters was the king -- a true genius. He was number one. There is no number two."
When Newhart was first "toying with the idea of doing stand-up," he saw Winters play Chicago's Black Orchid.
"I went in to see Jonny and to take a look at what it was like to be a stand-up comedian. And I thought to myself, ‘Well, he's the best. There's nobody better than Jonny, so why even try? That's as good as it gets. ‘ "
"But then I thought, ‘You know, fourth or fifth isn't terrible.' "