Got this off here. Had one ages ago and had a bout of nostalgia. However other gear calls. Really amazing analog synth from korg. Amazingly deeper controls that how things look. I post the detailed info from the seller I got it from:

Used - Good Condition

• Chassis: the wood paneling on the top and sides as well as the wood panel on the bottom shows some obvious scuff marks, scratches, dings, and dents from years of use and being transported; the top control panel as well as the metal front panel and rear connections panels have some noticeable scuff marks, scratches, and spots of paint loss
• Buttons, Switches, Knobs, Sliders, and Pitch Bend Stick: all move nicely and work properly
• Keys: all the keys show a few light scratches on them and move properly, however when using the Percussive sounds, all the F-keys do not work, but this does not occur when using the Ensemble sounds
• Jacks and Connectors: all the jacks are intact and function flawlessly, and the power cord just has a some very minor scuff marks on it
• LED Light: the LED light functions properly
• Includes: 48-key keyboard (manual, keyboard stand, pedal, cables, software, and case/gig bag not included)

Features

• Polyphony: 48-note for thick, layered sounds
• Sound Sections:
  Percussive: Electric Piano, Clavinet, Piano, Harmonics
  Ensemble: Brass, Organ, Choir, Strings I & II
• Effects: Built-in analog chorus and tremolo (with adjustable rate)
• Controls: Sliders for mixing sounds, joystick for pitch bend/modulation, and dedicated controls for Attack/Release on strings
• Architecture: Dual-layer system allowing simultaneous layering and balancing of Percussive and Ensemble sounds
• Outputs: Stereo outputs, mono mix, headphone jack, sustain pedal input, and expression pedal input
• Dimensions: 32.4"W x 5"H x 19.6"D
• Weight: 33 lbs.
• Made in Japan

The Korg ES-50, known as the Korg Lambda, is a 48-key polyphonic ensemble synthesizer produced from roughly 1979 to 1982, famous for its lush string, choir, organ, brass, and electric piano sounds, built with divide-down tech, analog chorus, and separate envelopes for layered, full textures, making it a classic for vintage pads and background textures, not complex lead synths. The Lambda is a solidly-built instrument, and its large top panel is perfect for laying out some effect pedals and/or a mono-synth. Despite its preset nature, the Lambda is a more versatile synth than it might at first appear, partly due to the quality of its sound, but also the simple yet useful modulation and tone-shaping controls. It really shines through a phaser and some reverb, and is eminently playable. You'll have no problem finding a place for this in your synth collection!