I like building high power amplifiers with tubes like GU74b, 4CX1000A, GS31b and others.
I have one commercial amplifier in my shack. It is an ETO 91b by Alpha with two GU74b tetrodes.
Most of the time I am running my homemade amplifier with a 4CX1000A tetrode. 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!