We may be going for a record here; this Broadcast Electronics FM20T was placed in service on June 6, 2001:
The original 4CX15000A tube is still in use. I wrote about this a few years ago in this post: Longevity.
I thought by now, we would have changed out that tube. A few quick calculations shows that the tube has been in use for 118,289 hours or 4,929 days or 13 years 6 months and 3 days. Anyway you look at it, that is a long time for one tube in nearly continuous use. I noticed the hour meter is lagging a bit:
Reads 113051.24, which is 5,238 hours different than what I calculated from the maintenance log. I noticed a slight discrepancy in hours two years ago and attributed it to various off air periods. However, between then and now, this transmitter has not been off at all. Thus, the hour meter is wearing out before the tube. I would say that this is because of excellent filament voltage management, but I think we simply have a really good tube.
Has anyone else had a tube that lasted this long or longer?