After reading issue 19 of 'Vacuum Tube Valley' (http://www.vacuumtube.com/ ), I'll be expanding my 'collection' of Ei KT90s and using only them in one of my c-j Premier Elevens. The other will get the new Sovtek plastic-base 6550s (only $39 per bias-matched pair) that I bought.
You probably should buy and read that issue.
You probably should buy and read that issue.