FU728F の本来の評価 Poor quality and long term reliability Time Owned: more than 12 months. While I was also a believer in the hype regarding these tubes. The 1st tube that I had that I bought with the AMP lasted 1 year. Then i had a real battle finding good spares. I tried the Ebay route and all the tubes are gassy or failed rejects. I ordered 6 tubes from different supplies all were gassy and arced over. I did follow all the procedures to condition the tubes, including running the filaments with grid bias and heater voltages for 1 week. Same result tube arced over. I went from Ebay to Ali-express with sellers offering a guarantee for 60 days same thing tubes flashed over in less than 1 month of intermittent use. Then I bought 2 x tubes from OMpower at great expense. These tubes were supposed to be conditioned and tested.and over 4 months of rotation and intermittent usage they failed as well. Either i am jinxed or the tubes are really crap. The end result is that I have been unable to find a trusted and realiable source for these tubes. The prices have also gone through the roof and for such an unrealible tube its becoming a real rip off. I had my Dentron MLA2500 with the same pair of 8875's for 25 years. I still have by TL922A with Eimac orginal tubes still going strong at 1200 watts output with no faults. I have a homebrew 6 metre amp with 4cx250b's thats more than 30 years old with the same tubes that has been through hundreds of contests and the tubes are all good. From this perspective you can see how crap the FU728F's really are.