Music in season 6 is credited to Pete Rugolo. Looking up some tv shows he wrote for I found The Survivors.He's credited for the music in 7 episodes.

Interesting thing is I was able to go to a shooting of The Survivors. Apparently the first TV mini series.

https://m.youtube.com/watch?v=0VEFMWOWVv0

Other than "jazzing up" the main theme, they did get Rugolo and overhauled all the music cues in the show. As a result the whole feel of the show was more modern.

I believe Rugolo was himself responsible for the jazzed-up version of the theme as well as writing all the incidental music for the last season. From what I've read, Rugolo was a skilled, classically trained composer (he studied with the French classical composer Darius Milhaud, no less) and a notable name in the jazz world. His talents were a boon to LITB, similar to Vince Guaraldi's work on the "Peanuts" shows.

I believe Rugolo was himself responsible for the jazzed-up version of the theme...

Yes, my post was poorly written. That's what I meant to say.

Particularly early on they were using common cues from the Capitol Music Library. Earlier George Burns used several of the same cues on his show's fifth season.

By the fourth or fifth season of Beaver they were updating the music, somewhat. But the final season was a total revamp by Rugolo (mis-spelled Rugulo in one episode's credits).

Rugolo died in 2011 at the age of 95.

FWIW, I just noticed tonight that Rugolo was credited with music on the episode of the Fugitive that I just watched. And, I guess most other episodes, as well.

He's done a lot TVShows-scoring. I love the jazzed-up opening/closing better than the older shows. Definitely a major contributor. Look him up on IMDB for ALL his credits!

What's interesting, re the jazzed-up theme, is that I have a CD remastering of a record made in, I think 1958, that contains big band arrangements of TV themes. LITB is on it, and it is a swing arrangement. So the possibility of jazzing up the theme was apparently there from the beginning.

Here's a short article about Rugolo and the theme/technical credits opening theme:

https://www.allaboutjazz.com/news/pete-rugolo-and-the-beaver

Here's an early 60s Rugolo album TV of themes in stereo (Unfortunately, pre-Toy Parade for LITB)

https://www.youtube.com/watch?v=DN9R8M_LbIo

I was looking for the LITB theme by him in stereo, but it evidently doesn't exist.

Rugolo's version is my favorite. I like that it's upbeat with more energy to it.