Barry - Your speakers can probably be serviced by long-time Thiel service manager Rob Gillum now of Coherent Source Service in Lexington.
The O3a is second generation O3 which put Thiel on the map. The A generation dealt with baffle edge diffraction via wool felt absorption - very effective but somewhat homely-looking. Your cabinets are made of Finland-Ply (high-end Baltic Birch), similar to the latest CS3.7 and 2.7s curved ply panels. You also got the first dose of styrene ultra-bypass caps. With the equalizer, you can get sub 30Hz sealed box bass from that heavy-duty custom Eminance woofer. The O3b added some driver refinements and more precise time alignment. The CS3 incorporated a curved-edge baffle for geometric rather than absorptive diffraction control and an all new driver complement. The CS3.5 (5th generation Model 3) still stands an an epitome the design family. If parts were readily available, which they are not, I would like to hot-rod the CS3.5 as a tribute to its place in the development of high-end audio.
The point is that each successive model generation applied new ideas, techniques and technologies to stand on the shoulders of its predecessors. The O3a is a true minimum phase, minimum diffraction, extended range Thiel speaker. It is probable Rob can keep them on the road and their performance will embarrass many contemporary speakers.
