I run my monoblocks fairly easy, 29 watt plate dissipation,
20 watts output PP triode, and only one highly used Sovtek
and SED tube has failed, both old but I don't the hours.
Among the new Tung Sols I saw just a $7 difference between
their 6550 and the KT120. If they sound the same, why
not purchase the KT120. Fil no problem. I could jack
the plate voltage for a little more power output for
better side getter gas absorption.