Bumped into an old mate of mine last night at a gig -not seen him for years and he sells very high end valve-driven HiFi (can I plug his URL? - Mod- remove if not appropriate!) www.aliumaudio.com We got talking about swapping tubes about from the standard 12AX7 and so on for others that he uses in his amps (bloody expensive too!). I might see if I can borrow some of these tubes and swap 'em about in my Fender BJ to see what happens. He hadn't thought about the application of these hi-end expensive tubes in guitar amplification so I offered to help! It was just funny to speak to someone who knew what an ECC 83 was!