Jack Hertz Report post Posted June 2, 2017 The Metasonix TS-23 is a basic VCO, much like that in any modular analog synthesizer-- with a big difference: it is a dual VCO, and it is made of thyratron tubes, types 2D21/5727. Such tubes act as relaxation oscillators, and give highly imperfect sawtooth waveforms. View full synthesizer Share this post Link to post Share on other sites