The pic below is a scan from the Sunn Master Parts List dated August 1, 1978. It lists speaker replacements for a Stage 115, Stage 212 and Stage 410. Since the Stage series is not in the 1975 or 1979 catalogs, I would assume they were available between those times. The wood looks an awful lot like like a Beta 410. Please post the dimensions. Perhaps the Stage series was a precursor to the Beta series, just a stripped down version without the channel switching. Anyone know of an amp that used a white power switch like that? It looks like the one used on Coliseum amps only white.