I recently acquired a McInstosh 240. Its Unity Coupled output stage requires no biasing after tube swaps, which makes it an ideal test mule for swapping and reviewing 6L6 tubes. Let me preface this by stating that this is a hi-fi review, not a guitar review. Both have subjective components but a hi-fi review probably requires a bit more objectivity as "fidelity" is in the name. Unfortunately, I have not unpacked any of my test gear since moving back East. Having said that, I do play guitar an look forward to testing these tubes in a guitar rig. After hundreds of hours of listening, it is clear to me that this would have been the standard by which current production 6L6's would be measured. Unfortunately it is no longer produced and I'm trying to find a successor. While the amp itself is a critical link in the circuit, I didn't know tube amps could produce so much bass before listening to this tube. The bass is deep and controlled and smoothly transitions to mid-range with no coloring. The top-end is pleasant and easy to listen to. Now let me get subjective for a moment. This tube in a MC-240 is magical. I cannot pinpoint where or why, but I suspect it is in the mid-range and is probably the "tubeness" that people rave about. There is absolutely no fatigue, and I can (and do) listen for hours. It's hard to explain, but at the first note played, I want to say "OK, this is a nice tube" but somewhere around a half-hour later, you realize that you have been experiencing audio euphoria. No one snapshot in time reveals the euphoria, but rather it is like a mathematical integral where you realize the area under the curve has been accumulating. Definitely a great tube, though at a premium.