Update
The circuit seems to work ok as drawn, but can clearly be improved upon. The first 'upgrade' I will try is a faster opamp, b/c my layout is for a quad package. If this is not satisfactory, I may redo the layout to allow seperate triangle gen opamps and comparator. The switching freq is so low (50khz) that a 'faster' comparator may not squeeze any more out of the design, IMHO. In the text accompanying the original schematic it tates full range operation to 60w in 8 ohms. Off the top of my head, 51v is not enough to quite get there into 8 ohms. Also, 50khz switching does not seem reasonable for full range use. To me, these limitations are acceptable as I am attempting a very small subwoofer with a linkwitz transform eq, which brings me to my next questions:
Keeping in mind the low switching freq, mount the amp right next to a SHIELDED subwoofer and use shielded cable for the few inches to the terminals, and I think I may just get away without using an output filter...
I expect there are a few things to spoil this plan, like heating in the voice coils of the woofer. Any thoughts on this?