One of the final vacuum tubes for KGEI's 50kW transmitter. Note the water jacket and copper tubes that circulate water from the downstairs cooling system. These tubes cost around $1200 (probably around $5000 in 2005 dollars) each and were rated at about 3000 hours. However KGEI often got considerably more than 10,000 hours out them. There was also at the time a "cottage industry" in tube repair for this type due to their widespread use in radio. Photo courtesy of FEBC.