For those that are not familiar with the YU148 or 3CX6000, it is the most horrible tube fausted onto the broadcast industry since the 5CX1500. IIRC, CCA was about the only broadcast manufacture to use them.
Oddly, the only remaining CCA FM10000g that I maintain used to require NEW Eimac YU148's but seems to suddenly be very happy with rebuilds. We are getting at least the same life out of the last 2 or 3 Econco YU148's as we did with new Eimacs. Back when that TX was reasonably new, a rebuild's life was often measured in weeks. A really good bright shiny new YU148 gave about 12-14 months at 9kw. The last 2 or 3 Econco rebuilds that I have installed have gone at least 12 months.
But that is the only bright spot in the tube world as far as I am concerned... Due to all of the trouble with tubes and tube life, I have totally stopped supplying tubes to to my few customers still clinging to tube transmitters. I will help them order tubes and will install them but will not provide any warranty, return shipping or guarantee what-so-ever. Since instituting that policy last year, I have heard a lot less griping about how much tubes cost and how often they have to be changed.