Casio PT-80

This keyboard has many similarities with the Casio VL-Tone 1 and PT-1, but includes a "melody guide" key lighting feature for music teaching (not the keys itself light up but a row of small LEDs above them) and a ROM- Pack music cartridge slot.

Casiotone 401

This was Casio's first keyboard with accompaniment and (so far I remember well) also the world first keyboard with automatic single finger accompaniment.

The Casiotone 401 has 16 unusual, partly incredible dry semi- analogue preset sounds and 16 analogue rhythms; also the bass sounds nicely warm and seems to be based on a triangular wave. Unusual is the "hold" switch, much like the manual fingered chord mode (with chord memory) on newer keyboards, here also the melody voice notes hold until any other chord or key combination is played. The noble designed case is unusually heavy, because it is made of plastic coated steel instead of genuine wood

For Sale, pub-8492136789179150, DIRECT, f08c47fec0942fa0

Casio PT-20

(photo from eBay, showing my specimen)

This tiny instrument seems to be just a downsized Casio PT-30 and sounds very similar. (I haven't examined the hardware yet.) Unlike the latter it is missing the LCD, the cartridge slot, some of the sequencer buttons, the transpose buttons and 2 high note keys (thus also the "arp. 6" rhythm). Instead of separate rhythm and chord volume sliders it has only a combined slider. Its small case resembles the Casio PT-1. The original German retail price in a German Conrad catalogue from 1986 was 199DM (about 100€).

The likely most advanced member of this hardware family was the ultra- rare keyboard boombox Casio KX-101 (37 mini keys, chord button pad, complex sequencer that saves data on audio cassettes), which was even 4 note polyphonic.