I was on the forum yesterday reading posts, which is how I happened across Bob's SCA-35 EFB post. Since my mind was on what I was searching for, and not the EFB, I neglected to mention one important fact about the simple bias modification: Output tube life.
When I decided to bring my SCA-35 out of mothballs for another try, I figured I'd get some good output tubes to judge it fairly. I wrote Jim McShane to ask about the Gold Lion EL-84 's I had read good things about. Jim was concerned about Dynaco biasing the 6BQ5 at 35 mA in the SCA-35 and ST-35. He was hesitant, since he knew the Gold Lions wouldn't last long biased at 35 mA. I happened to mention Gillespie's bias modification (which lowers the bias from 35 mA to 27 mA). His reply was that I could trust whatever Dave Gillespie said, and that he'd be glad to sell me the tubes if they would be biased at 27 mA.
I bought the Gold Lions (love 'em!) and don't mind running them, since I know they're going to last me a lot longer with the EFB mod.
Tazsmonn, I can respect your purist take on tube amps. But to me, if it's going to make my expensive output tubes last longer, and sound (and measure) better doing it, then I'm all for it. Oh, and I agree that an adjustment for each output tube is better. That's the way I'll be building the bias supply for my ST-35, using the EFB circuit, but with one pot for each tube.