The JJ EL34 when played clean is nice and linear, not top or bottom heavy just nice and centered. Overall this valve is smooth and rich with fairly complex harmonics. When pushed into distortion the thicken up and bloom.

Platinum Matched & Tested

We burn-in these valves for a minimum of 30-40 hours before matching. The reason we do this is to get rid of any faulty or weak valves and as a pre-grading process to allow the plate/grid mechanism to relax into it's rest position. Tiny differences in construction make for enormous differences in electrical characteristics, and thus if a tube is graded after it's been burned in then the measured characteristics hold true over its lifespan to a greater extent.
This seems simple but it's amazing how many vendors ignore it. It's the reason so many people complain about poorly graded valves.