As just one example, my Ref 150 SE which I purchased new in 2017 has a design problem with in-rush current on start-up. It is not a question of if, but when, as to the input fuse blowing and taking the board out with it. The successor 160M, 160S, and 80S implemented a relay-circuit with soft-start.
@fsonicsmith1 There is an inexpensive device called a current inrush limiter that is a kind of thermister. Any technician can install one in minutes. We've been using them for decades. When cold it has a higher resistance; when you turn the amp on, the current thru it causes the resistance to drop as it heats. Very simple and reliable.
I think you are right about the KT150. IMO if you're going to use an amp using hi powered pentode power tubes, the KT88 is still the best option- there are good quality KT88s available from JJ.