Sunnyjim---To be aware of the "pre-AMT tweeter and Dr. Heil" era ESS, you are either as old as I or a Hi-Fi historian (or both)! I happen to have such a pair of loudspeakers, the ESS Trans-Static I's. I found them in L.A.'s The Recycler paper in the mid-80's for $400 ($1200/pr retail when new), in good working order except for one woofer being a cheap imitation of the original Kef B139. I called ESS and was told they had one remaining B139 in stock!
The Trans-Static was a pretty advanced loudspeaker when it was introduced (1970, I believe), having three RTR ESL tweeters operated open baffle/dipole, a Kef B110 5" midrange driver loaded into a short (15", the depth of the enclosure) transmission line, and the B139 woofer (which Dave Wilson used in pairs in his WAMM loudspeaker later in the decade) with a long folded-transmission line behind it. X/O frequencies were 275Hz and 1500Hz (designed by a young John Ulrick, cofounder of Infinity Systems, and now owner/designer of Spectron Audio), and each speaker weighed a substantial 139 lbs. They still sound pretty good!
