@russellrcncom
I can't speak to the pre-amp upgrades but in terms of the CJ amp upgrades I have some experience.
I was very curious about the Teflon cap upgrades for older CJ amps. I have had my CJ premier 12s for over 20 years but wondered what they'd sound like with the cap upgrade. However I didn't want to risk spending the money only to alter the sound to something I didn't like.
I was fortunate to find a good deal on a pair of Premier 12s that had the full Teflon cap upgrade so I bought those to compare to my original 12s. I would keep the one I liked best, sell the other one.
I ended up keeping my originals.
The Teflon 12s were fantastic. The first thing I noticed was the increase in soundstage and imaging scale, which blew me away. The other thing was the apparent "blacker background," lack of grain, finer nuance, and increased resolution of the acoustics and reverb in recordings. Also, bass was more controlled and refined.
Sounds all "win-win" doesn't it?
However I also found: My original 12s sounded a bit more dense, punchy and ballsy. And they had the tone that I've always liked. The Teflon 12s had gorgeous tone too, but I was sometimes left a bit wanting in density and punch.
One major factor was that the Teflon 12s came with KT120 power tubes rather than the 6550s that I've always used. Just to check I switched those KT120 tubes in to my original 12s and...whaddya know? A bunch of what I heard switched to my original CJs: that same enormous soundstage and imaging, slightly better sense of hights/detail retrieval, and deeper slightly more controlled bass.
Now I was getting closer to the best of both worlds - the original tone I liked but improved in some ways.
So ultimately I felt I wasn't justifying keeping the Teflon 12s, and those would be easier to re-sell anyway.
Admittedly I do occasionally pine for some of the things I heard in the Teflon 12s - they sounded so gloriously free of grain and transparent and beautiful, and I liked that bass control which my original 12s never quite reached. But, compromises are compromises.
Being a crazy audiophile, I'm actually considering sending my Premier 12s to Bill Thallman some day in the future, just to try the different caps he uses for the upgrades (e.g. V-Caps which many rave about - he also uses the new Wilson caps).
In fact I might send my CJ Premier 16LS2 to him first for an upgrade. Last year I bought a Benchmark LA4 preamp and I'm loving the added clarity and lack of grain over the CJ preamp. But the CJ preamp still does some more tubey magic. I'd like to hear what a Thallman upgrade can do for the CJ preamp.
