You could (have) used a fuse of the appropriate rating to sub for the circuit breaker. too often as you have seen, the CB is bad.
I have seen the ctc-15 design in an early 70's Wards set so it was in use at least till that time. They just added in the pincushion components for use on the rectangular tubes.

If that were a pic. of Poppy Montgomery (CBS Without a Trace - thursday nights) On the screen in the first post instead of Roger Ebert I'd haveta make it my Desktop wallpaper. What a great picture! Man I'm jealous. Right now I've got one 21fjp22 in a 65 vintage Zenith (the one with the Vhf and Uhf tuning knobs mounted diagonally from each other) that has a bad 3.58 to demod driver xfmr and a rough cabinet and a Curtis-Mathes entertainment center with a bad flyback and crt. That 21fj mite end up in the c-m befores the days end. I've gotta fly for it and now I've been inspired. My ctc-20 needs a companion. I still doubt though that the picture will come anywhere close to that Silvertone. That thing just looks waaaaay sweet!

(Jeffhs' post is too long to quote )- but regarding the question of "marketing agreements" - no, that was not a marketing agreement, but the companies with small design staff were buying the RCA patent license package. This gave them access to the RCA chassis design as well as the basic technology. They had varying success with copying the RCA design, especially in circuits where stray coupling could cause a problem - same schematic but different layout could give different results.
Large companies, Zenith in particular, fought the RCA licensing for years, taking it to higher and higher courts until RCA was forced to unbundle implementation patents from the basic technology patents. Meanwhile, these larger companies spent money on finding ways to build receivers that didn't require the RCA implementation patents.

I knew someone who went from Motorola to Admiral, where they basically licensed the RCA design. He learned a lesson from that and went on to become a patent lawyer.