Trimix
The Trimix was a mobile console using the same circuitry as the Series 80. Released in '81, a year after the original 80, it was
a split 8 bus design available in either 16 or 24 module widths. There was also a matching patchbay sidecar available. In '83, the Series 70 was introduced, which used the Trimix modules in a large format frame and modified them for 16 busses. While the Trimix used 8 individual bus selection switches, the Series 70 was modified to select bus pairs with the same switches. The Series 80 used 12 switches in pairs for 24 buses total. The other differences between a Series 80 and a Trimix/Series 70 module were the hi and low shelves weren't switchable on the latter, thus 80/120Hz became 100Hz and 8k/12kHz became 10kHz, plus the stereo aux send was omitted. Otherwise, all three consoles used the same circuitry and had identical mic pres, sweepable EQ, etc. For this reason, much of what you hear about Trident Series 80 consoles can be applied to Trimix/Series 70 boards as well.
These are great rock and roll tracking boards with transformer coupled mic pres and a cool tone to the EQs. The Trident A range would be more comparable to a Neve or API as they were the first class A discrete Tridents, but only 13 were made. The Series 80 opamp designs built the reputation of the "Trident sound." Outside of the Neve, API, etc., class A discrete designs, there are few more desirable vintage mic pre/EQ modules than the Series 80. Considering the prices of new Series 80 re-issues, Trimix/Series 70 boards are a bargain.
Now the caveat, these are twenty year old split boards. A loaded 24 module Trimix frame consisted of 16 Input modules, 4 dual submaster/tape return modules, 1 dual master/tape return module, 1 aux master module, and 2 blanks. This would give you 16 channel inputs, 8 bus outputs, and 10 tape returns. At mix, you lose the 2 tape returns on the master module as you need to monitor the mix bus on that path, and you lose the tape returns on each submaster you use in the mix, as they are assigned to the master through the same path. So you can run 16+8X2, 16+4x4x2, or 16x8x2, etc. Not quite as convenient as an in-line Mackie that can run 24+24x8x2, but the sound... nuff said. Trimix frames can be linked to share the same buses, auxes, PFL, etc. to overcome these limitations, sound familiar? One PSU can power two 24 module frames.
Caveat two is maintenance. If every electrolytic capacitor hasn't been replaced recently, it should be. These boards are worlds easier to work on than a Mackie as they were designed to be servicable by non-techs. I just replaced two faders on a Mackie 24x8, and it required a total tear down of the console, so when the caps go, it's in the dumpster. On the Trimix, you pull the individual module, every part is labeled and the separate circuits are illustrated on the card itself. You continue using the board while the module is on the bench and you can test your fixes using a riser card so you don't have to re-install it in the board to listen. In other words, it's a real console. If you'd like to see pictures or schematics, just ask and I'll post some. HTH