I put them into my home-built version of the ST35. I've incorporated Shannon Park's Driver circuit (http://www.diytube.com/st35/ST35_REVD_2009.pdf
) which calls for a 12AX7 for voltage amp and 12AU7 for phase splitter although I'm currently using a pair of NOS 12AU7 tubes I got from Andy at Vintage Tube Services.
I'm sure you'll be amused by the giant blue caps in my power supply. They are Clarity Cap TC series 700V film caps. (http://www.claritycap.co.uk/products/tc.php
) I wanted to see if the lower ESR would make any audible difference over the panasonic electrolytics I had been using. Pretty sure it did. The caps are 45uF, 110uF, 110uF.
I also put in the Enhanced Fixed Bias (EFB) circuit by Dave Gillespie. As per Dave's instructions I set the bias at 27mA per tube.
What do I need to do to test the matching? I already have test points for the plates available. I can always add more. I'm actually considering rebuilding it in the more traditional way just so I can reach the tube socket pins easier. When I built this I just wanted to do something different.