So, I just purchased a pair of these and stuck them in my Ampeg Jet j-20. It's sort of a Brown Fender Deluxe clone with non-adjustable, fixed bias. It runs over 400 volts, and I previously cooked a pair of Tungsols in it. The JJ's sound GLORIOUS, but they're running 400 volts and 29ma, for just over 80% dissipation, according to Rob Robinette's bias calculator considering them to be 14w tubes (as indicated on the data sheets). All the research I've done seems to support that they'll function at this setting and again, they sound really good with no sign of red plating, even after 3 hours of play at full band levels. Some of the stuff I've found, including some torture testing by Lord Valve (I think), indicates that these things are nearly indestructible (I said nearly)! And, some of the stuff out there would suggest that they may be 17 or even 19 watt tubes (more akin to a 7591 or 6l6gb). Interestingly, Rob's calculator also has 15w to 19w listed under tube type. If I pick 17w the dissipation falls right on 70% dissipation. Anyone else using these tubes like this? Maybe we all should be! I will report back on longevity.