How long is the useful Life span of a tube? Let's use some well known tubes in AR circles as examples, a pair of 6146 final PA tubes or some 4CX1500Bs as examples. If these tubes are used correctly, operating environment maintained to specs properly, how long/hours of use are these tubes good for? Does Life span of the tube actually decrease significantly if you leave the tubes on 24/7/365 and in use such as in broadcasting application? I'm sure broadcast applications are more then bulletproof in their design and the use of the tube(s) in the actual Xmtr. I don't ever turn off my S Lines of any other tube/hybrid gear I am using during the Winter here in Tx. I see stories of folks using original tubes, in TS-830S rigs, FT-101s and other final PA tubes that came in these type of radios from the factory 25 to 30 + years. I believe K9STH posted a story about a Motorola radio that was forgotten about in a building and uncovered 20+ (?) years later and still worked when found. I ran across 1 of those pig in a poke type of deals. I bought 3 @ 4CX1500B tubes all used in some type of 4KW Xmtr. All 3 tubes were used in the Xmtr at the same time, so I am thinking the tubes weren't driven to hard in their lifetime. 1 tube has a stamp of 10,000 hours of use on it, which to me doesn't sound like much if the tube was never pushed to it's max for long periods of time. All of the 3 tubes are supposed to be full power out, according to the seller. The cost of all 3 tubes was 75.00 which seemed like a deal to me as I now have plenty of backup tubes for my 30S-1 amp.