Here's my experience.
I am using the specified fuse, which is 1A, slow blow.
I have run the unit with and without the input/output RCA's connected with no problem.
I have powered up the unit without the tubes installed with no problem.
On my initial start-up, I first triple checked my work, put in all the tubes, placed the unit in a open space area where any sparks wouldn't start a fire, and turned it on. Then waited for strange noises or smoke. No problems. Then I measured the output (no inputs) with a multi-meter to see if there was any DC or AC voltage. Nothing significant detected. Then I turned it off and hooked it into a cheap system I have and played it to see if it worked, which it did. I was fortunate that it worked the first time.