To bring up slowly you need a variac which is basically a giant variable resistor. You start out at 10% of rated voltage and bring it up in 10% increments every 10 minutes or so. I believe this is primarily for the capacitors, but it is good for tubes too. Some tube electronics have soft start circuitry for the tubes just to avoid shocking them on every turn-on. Six months of storage is borderline for doing this, if you know a good tech who would do it for low cost it would be worth it, otherwise it's a judgement call.
Powering up a SET amp after 6 months in storage
What precautions do I have to use in turning on my SET amp after it has been sitting unused for a number of months? I have heard the phrase "bring the amp back up slowly" in connection with tube amps and preamps, but I don't know exactly what that means, and if a tech guy has to do this for me. FYI, the amp has a mute switch in the back if that is any help. Thanks.