Not sure about the Sullivan show in particular, but the majority of the time he played a Rhodes Piano Bass keyboard with his left hand while playing the melody line on a Vox Continental keyboard with his right. They did usually use a studio bassist on most recordings but never live. Many of them had difficulties learning the bass parts as they were so complicated. I'm not a keyboard player and its always amazed me how they can play separate complicated parts with each hand. Yeah, that's why I try to keep the amazing decade of the 60's alive due to the intense innovation being demonstrated. It was long before digital recording happened and almost all of the techniques were organic. Not only were the musicians so inventive but people like Spector, Brian Wilson, Sir George Martin started exploring the use of the studio as an intricate part of the music. Take the chorus sound of 10cc's I'm Not In Love as an example: It is notable for its innovative and distinctive backing track, composed mostly of the band's multitracked vocals. Stewart spent three weeks recording Gouldman, Godley and Creme singing "ahhh" 16 times for each note of the chromatic scale, building up a "choir" of 48 voices for each note of the scale. The main problem facing the band was how to keep the vocal notes going for an infinite length of time, but Creme suggested that they could get around this issue by using tape loops. Stewart created loops of about 12 feet in length by feeding the loop at one end though the tape heads of the stereo recorder in the studio, and at the other end through a capstan roller fixed to the top of a microphone stand, and tensioned the tape. By creating long loops the 'blip' caused by the splice in each tape loop could be drowned out by the rest of the backing track, providing that the blips in each loop did not coincide with each other. Having created twelve tape loops for each of the 12 notes of the chromatic scale, Stewart played each loop through a separate channel of the mixing desk. This effectively turned the mixing desk into a musical instrument complete with all the notes of the chromatic scale, which the four members together then "played", fading up three or four channels at a time to create "chords" for the song's melody. Stewart had put gaffer's tape across the bottom of each channel, which meant it was impossible to completely fade down the tracks for each note; this resulted in the constant background hiss of vocals heard throughout the song. Composer and music theory professor Thomas MacFarlane considered the resulting "ethereal voices" with distorted synthesized effects that are an example of early synclavier music to be a major influence on Billy Joel's hit ballad "Just the Way You Are", released two years later.