Four channel version of the very successful TC-755 series : for surround thrills, there is nothing like four channels spread over four independent tracks.
Where the TC-788-4 differs from most other 4-channel offerings is in its tape speed (38cm/s, like the pros !), closed-loop dual capstan drive with one AC Servo motor plus two induction for reel spooling, feather-touch transport pads, and all the other reliable features of the TC-75x series - one of the 1970s bestselling series of reel-to-reel recorders worldwide.
Amp-wise, the inputs are FET-charged and recording bias is at a very high 160Khz ; concentric input and output pots can be pulled for -20dB gain for both front and back MIC inputs.
Price-wise, this was indeed for the pro : 248,000¥ in 1974.
Controls-wise... there is enough to get lost quickly if you keep in mind that four channel can also mean 4-channel in QUAD surround mode where record levels, balance and playback levels remain always set separately. The record modes, too. The panpots, too : left front, right front, right rear, right front and anything in between. For each of the four tracks. Like monitoring, left and right separately : Source right front or Tape rear left. Right front and Rear left denotes clear cut separation yet intimately intertwined relationships, otherwise the four parts that would make the researched single sound-field would become too obvious as being, really, four in reality.
Savior of this two-way dilemna : the headphones (plural : several phones for one head) which can be switched for 2-channel (two ears makes two channels), or 4-channels with the help of a second pair of headphones. But who can multiply ears so as to have two pairs in the end ? Simultaneously ? That would make four ears but although ears generally are on the side (one head equals two sides), which of those resulting four would be the front ears and which would have back-ears duty ?
Ah - modern world : it is crazy what one can do with one brain, two hands and four tracks.