Sequential Circuits Six-Trak with MIDI Mod

via this auction
"This particular unit has a small mod on the MIDI Out jack. A switch has been added to toggle between Out and Thru operation. With the switch set to “S-T” all MIDI data from the Six-Trak (notes, program changes, etc) are sent to the MIDI Out jack, but anything coming in the MIDI In is not sent to the Out jack. With the switch set to “Thru”, anything coming in the MIDI In jack is sent to the Six-Trak and the MIDI Out jack, but no changes on the Six-Trak (notes, programs, etc) are sent to the MIDI Out.

Features:
* 6 voices
* 100 user patches
* 6 oscillators – sawtooth, triangle, variable width square/pulse (modulated)
* Arpeggiator – Up/Down or Assign (as played)
* Sequencer – 6 tracks, 2 songs, up to 800 events
* Unison mode (all 6 oscillators, same patch)
* Stack mode (up to 6 oscillators, all different patches)
* Pitch Bend Wheel
* Mod Wheel
* Foot Switch Input - Sequence start/stop or Arpeggiator latch or Patch # up
* Outputs – Mono ¼”, (can also be used for Headphones)
* 49 Keys
* MIDI In, MIDI Out (or Thru, with installed mod)
* Internal 115v Power Supply"