I haven't really studied for any yet. I've glanced at the one on Angela's site.My interest is that I purchased the Nelson Audio EL34 that Wayne had on loan as a demo from a couple of years ago. I heard it on his 7 Pi's at his house when I first met him and just really liked the sound. Unfortunately I wasn't able to pay the dealer that day and needed to run it by the significant other first. So after a week or so I paid the dealer and Wayne shipped it to me. UPS promptly dropped it hard enough to bust some connections loose and break a few other things on the inside which I wasn't aware of at the time because the outside looked in good shape. Put the tubes in it, fired it up, and boom----the whole thing went up in flames. I decided then and there that I'd never have another tube amp shipped to me. I'd either buy a new one at the dealers or build my own. So I got into building simple headphone amps to get a feel for soldering and such and now it's time to try my hand at a full fledged tube amp. The first I've decided will either be a Darling or a 6EM7 SE amp due to the fact they are fairly inexpensive, simple, and sound pretty damn good, basically use the same PS, and I have the tubes. Then we shall move onto the EL34 which is always in the back of my mind.