[Penthode]

Off the top of my head, I recall RCA went though two basic main generations of design from 1946 to 1950.

Generation 1 up to chassis kcs27 (1946 to 1948): Includes the 7" and 10" direct view and projection sets. What distinguishes these chassis' is the split sound take of from the tuner, 6AL5 DC restorer in all but the TS621 and TS721 sets and RCA Synchrolock horizontal AFC (except for the TS721 which has the blocking oscillator without the sine wave stabilization).

Generation 2 chassis kcs28 to kcs46 (1948 to 1950): Includes the 10" (10BP4), 12" (12LP4) and 16" (16AP4 and 16GP4) sets. What distinguishes these sets is all have 4 VIF stages, sound take of at 2nd VIF, DC coupled video amplifier and Synchroguide AFC.

This is from memory and needs to be confirmed. Also there are a few errors on the "tvhistory" RCA 1946 thru 1949 page Steve referred to: the 8TC270 (16") was omitted and the 9T270 thru 9TC275 are all 16" (16AP4) sets, not 10" and 12" as indicated.