Citation 16: Labeled as Citation 16 on front panel. Has toggle switch for power. Has LED power output indicators. Brushed aluminum front panel insert.
Citation 16S: Labeled as Citation 16 on front panel with no LED power output indicators, just a blank black rack panel with a toggle power switch. Same driver boards as Citation 16.
Citation 16A: Labeled as Citation 16 on front panel. Has LED power output indicators. Marked as series "A" on back panel. Has push button power switch, slightly larger knobs with finer grooves, revised driver boards, revised silk-screening on back panel. Had 2 different color versions for front panel insert, brushed aluminum or black.
Citation 16AS: Labeled as Citation 16S on front panel. Marked as series "A" on back panel. Blank black front panel without LED power indicators, with Citation 16A driver boards, minus the LED power output indicators. Push button power switch.
The "S" versions were for "short" meaning that they were short (or missing) the LED power output indicators. Front panel labeling on the different versions was confusing.
All 4 versions had 2 neon AC power indicators to the left of the power switch on the front panel, one for each channel's separate power supply.
Very rugged idiot-proof home consumer stereo amplifier that was used often as a commercial grade amplifier in clubs because it was "built like a tractor", as Robert Greenberg said in 1976, then president of H/K.