The pictured XO looks just like mine. If 2951-2 look like that, they're from the same era. Those black caps are polyester-mylar (one down from polypropylene), the coils are well-made from CDA-102 wire, which is high-end regulation wire, one step down from Thiel CDA-101, which is the best available. I tested these resistors and found them to be the non-inductive resistors that Jim had designed and made by ERSE. Although they look like normal sand-cast, but are better. Note that these PCBs are actually point to point layouts with no traces that can cause troubles. This wire has Thiel signature teflon insulation. All in, I would be happy with these boards, unlike some we have seen with obviously poorly wound coils and unknown insulation.
That said, if you're DIY-inclined, you could elevate the sonics by upgrading all resistors to Mills MRA-12s and all film caps to CSAs with the 100uF electrolytics to some upgrade recommended on this forum. I have eliminated all electrolytics and have developed an affordable CSA-type 100uF cap that works well. Not ready yet.
I don't want to open Pandora's Box regarding product iterations and quality levels. I'm told that all 2.4s were assembled in Lexington, approved by Jim and tested to the historical standards. I have expressed my personal disappointment that some particulars of parts quality eroded after my watch. But, compared to competitive products in design and execution, I suspect Thiel stayed way up on the value charts.
