The ABX was built in different sizes. The suffix -18 indicates the number of input channel slots in the frame. Note it doesn't necessarily mean there are 18 input channels installed. You may have fewer with the empty slots (hopefully) covered by blank panels. IIRC, ABX-14 was the smallest and ABX-34 was the largest, however there were at least two ABX-42 consoles built. Those were on the secret menu.
An ABX-18 is a charmingly small production console. These were designed primarily for radio production, but they were multipurpose. I have seen them used in production, TV and on the air. Note they are broadcast consoles, so some of the features were different from what you would see on recording consoles. Notably, the multiple output stereo mixes.
The ABX used a 990 for the summing amplifiers on the main stereo output mixes. Program, Audition and Utility all used the 990. There was an option for an output transformer, but those were rarely ordered. It's more likely this console will not have output transformers. It will have a very robust output amplifier however, on the main outputs. We called it a DA output and it was capable of driving multiple 600ohm loads.
The line input channels did not have transformers on ABX. It was an instrumentation type opamp circuit. If you get ahold of the schematics, you'll see some odd circuit values, at least they won't be what you would expect. We used a lot of techniques to keep RFI out of the circuitry. Remember, these were used for broadcast, sometimes installed near a transmitter/tower. Keeping the audio clean was not easy.
If you have any questions about PR&E consoles, I was a console designer there for more than a decade. I'm happy to answer any specific questions you have.
Catfish
