Mentioned in an incoherent Matrixsynth post in 2009 and almost ignored since then. As far as we can find, it was made in 1958 and uses twelve Tesla bench audio oscillators to generate an octave (FYI the Tesla company was the largest electronics manufacturer in Czechoslovakia in the Communist era); with unspecified top-octave dividers to do the lower pitches. Might be all-tube as far as we can tell. It appears to have primitive pitch and other controls for each key. Thus is more like an electronic organ with expansions than anything else. “Synthesizer” is really pushing it. Three whole octaves!
Anyone wanting to learn more will have to physically go to the Czech Museum of Music and ask intrusive questions. Only one was built and it’s kept in a sealed glass case.