Oli,
In the Sunn catalog thread, the earliest listing of the 190B was in the 1972 catalog. There is no 1971 catalog in the thread, but the 1970 flyer still lists the 200S. So the crossover period was likely less than 3 years. Loudthud noted that he has a 190B with a sticker over the silkscreened logo (200S). I owned a 1973 190B with the same sticker, solid state rectifiers and no punch-out for a rectifier socket. So clearly some 190B chassis were just re-badged 200S chassis when it still had a tube rectifier. And some of the re-badged chassis came without the tube rectifier socket punch-out and solid-state rectifiers. So, Sunn probably made the change to solid-state rectifiers during a late run of 200S chassis, and later re-named the amp 190B, hence the sticker applied to both versions of the chassis.
The weird things about this 190B on eBay is the warranty card dated 1978 (did Sunn transfer warranties to 2nd owners, or did this amp sit in a guitar shop for 6 years?) and the tube chart shows three 12AX7 preamp tubes (a left-over chart from the Sunn Studio PA?).
Ryan