If I recall correctly, the LS100 uses a pair of the 6SN7 and one 5AR4/GZ34.
Various 6SN7 tubes may run for as much as 50,000 hours. A Mullard 5AR4 has been reported to last the life of your component, but some current production 5AR4 rectifier tubes sometimes only last for a year.
A lot depends on the gear and the particular quality of tube.
