Fran,
There were two that I have fond memories of using...the '73 Traynor BassMaster Mark II (tubes).
and the newer Traynor Mono Bloc II (solid state).
Both were sold as seperate heads and both were usable for keyboards with the right speaker cabinet(s).
Most used two Celestion 12" full range for best results.
Back in the day, there weren't a whole lot of speaker/amps available for keyboardists.
Just as an aside, one system I used for amplifying the keyboards in my avatar was a pair of customized Fender Twin Reverbs with Celestion full range speakers and added tweeters (2) in each cabinet (with custom crossovers). The Polymoog sounded excellent through tube amplifiers, as did the Wurlitzer 200 piano.
Ian