Central Electronics was one of the early SSB rig manufacturers and produced several variations having the same basic phasing design. The 10A, 10B and 20A used interchangable phasing networks and all could be used with the optional VOX module. The 10A was first, of course. I've heard that CE offered a 10B upgrade kit, for ambitious 10A owners wanting the refinements of the 10B.
The 20A sported a bandswitch rather than plug-in coils.
See Central Electronics SSB Accessories