I like building high power amplifiers with tubes like GU74b, 4CX1000A, GS31b
I have one commercial amplifier in my shack. It is an ETO 91b by Alpha with a
couple of GU74b tetrodes.
Most of the time I am running my homemade amplifier with a 4CX1000A
That tube was originally a spare for a 30S-1 by Collins. It was more than 35
years in the sealed box before I bought it from a Radio Amateur on Ebay.
That was amazing!