Yes, as Bob says, it was "all of the above." At Abbey Road there were (back then) three chambers. The one The Beatles used the most was the one in Studio 2. It had several clay pipes placed randomly around the room, and was mic'ed with Neumann KM56 valves. I have used it many times, and it was indeed amazing; short delay, but very much character. Not sure, but it may still be there. It was to Ringo's left (if you look at the photos of his drum kit in the back corner of the room. The door to it was under the clock in the centre rear.) AR also had great EMT plates.
At Stax we had a couple of very wierd chambers, concrete, long, narrow, dank, wet, and the home of a rat or two, down in the basement. But they, too sounded awesome. I think the mics there were EV's.
EMT plates were heavily used in the 60's.
Here at Compass Point, I recently cleared out all the old equipment, boxes, and other assorted collected junk from one of the two old chambers upstairs. I put one KRK speaker in it, and two Beyer mics. The sound of it blew me away. We have good EMT's and I use them and love them all the time. But this chamber...wow.
The convenience and space saving of modern digital units makes them attractive, inexpensive, and easy to patch in and use. But there is no comparison to a GOOD chamber or a well tuned plate.
Best to all,
Terry M