Hi, I get asked all the time on the Oddblock amps as to how often the tubes should be replaced. I used the original tubes (blue glass JJ KT88s) for 12 years in class A U/L at 36 watts dissipation (A+S) and they still were sounding fine and tested good. My estimate was nearly 8000 hours. Well beyond the 2K or so they spec for. Since I switched to the KT120s in the amps I figure they will last to the next century at about 25 watts dissipation. That BTW is a sweet spot in the sound, not done to be be frugal. The preamp and drivers either NOS Phillips JAN 5751 or NOS JAN Sylvania 12SL7s will likely never need replacing. In the past 15 years I have had one fail due to an internal short but none ever tested or sounded bad. BTW I suspect the Blue JJs were probably not no lead but I could be wrong. Sometimes the socket is the issue and not the tube. I normally use Belton ones. They can be testy as they grab the tube really hard though and can make it difficult to get out. I now always use SMPS for heater power that are well filtered, isolated and closely regulated.