Yes, the Sonaro is the mystery amp.
I wish Conrad himself took on this discussion and put it to rest once and for all.
I am going to take mine apart and get some good photos and post them. May be somebody can spot some differences. I don't think they even bothered to document them with schems because in essence, it was the 200S or Sorado.
My oppinion is that in late 69 or 70 the Sonaro went with the standard (2) 6550's line ups and used the same transformers that the Sorado and the 200s had. Then the only real differences were in the names and speaker configurations. JMHO.
That way they could reduce their inventory even more while they were gearing up for the solid state stuff
Mark