FWIW, I bought my CT-150 back in 2001 (Circuit City floor demo). It died about three years ago. When I opened up the amp, I found the filter caps had failed and took out the bridge rectifier (possibly vice versa). I replaced the caps and bridge and she's still running fine today. I did double the caps, as the board was marked but the factory hadn't installed them.
Otherwise a *very* tough sub. Definitely nowhere near as low and loud as later designs, but the protection circuits are so good that I've never heard her protest no matter how atrocious the signal or volume!
I had a newer (2004-ish) Velodyne subwoofer amp die and I sent it in to Velodyne for repair. It was back fairly soon after and I happily paid the $230. It did not need to be replaced, they just repaired it and the sub sounds as good as new. The sub's circuit board was easily removed with just 4 screws and two wires needed to be detached (they had spade lugs so no wires needed cutting). It cost less than $10 to ship it. For me, the worry about matching, tuning, etc. was enough to just pay them.
Of course if you have lots of time on your hands and want to tinker with the sub, then by all means figure it out! I had better things to waste time on <g>.