3 Attachment(s)
Summary 1: Central Casting.
To give an initial summary of the evolution of the Wadkin RB buzzer, I'll start with the Central Casting (for want of a better name) - the casting that mounts the cutterblock.
I've found no pictures of the earliest RB, from the time it was classified RC. From the pictures I do have, it appears there are just two variations of the central casting:
First the "high arch" model...
Attachment 409205 RB 183
...found on RB 117 (pre-1937 - possibly made in 1928-29); and RBA 183 (of 1937).
Followed by the later "slotted" main casting...
Attachment 409207 Attachment 409206 RB 921
...found on the other RBs in the sample, from RB 512 (date unknown) and (RB 563 of 1947), to RB 1010 (of 1954).
Going by serial numbers, there were 568 RBs manufactured between late 1947 and late 1954, which equates to ~65 per year. If we can extrapolate, that suggests RB 512 was probably made in early 1947 - leaving a nine year gap between RBA 183 in late 1937 and RB 512 in early 1947, for this change to have occurred.
Cheers, Vann.