Probably too late now. The first thing I would do is to Open It Up. Check for over heated resistors, leaking capacitors, burnt wires, dead roaches... And while you are in there change the output ohms tap. 10 years. Might start thinking of recapping the unit.
Test the Tubes. Find someone who has a Tube Tester. Or buy one. Mutual Conductance Tube Tester. You're getting into tubes. Mind as well start getting the tools to support your hobby. Write down the values of each tube. Check them every 6 months to a year. See if the values are deteriorating.
If it has been sitting or stored for a while, I would do a slow power up without the tubes. But you probably don't have a variac. Remove the tubes. I usually put in a smaller rated fuse in but eh, lets chance some excitement. Plug it in, get ready to jump away and flip the switch on. No pop, sparks or flames you doing good. Put the tubes back in.
Checking the Capacitors. I would have done this when doing the internal inspection with a cap tester. Hook up the speakers, turn it on and listen for a 60/120hz hum or buzz as the tubes warm up. Should be dead silent. If you hear anything, probably the filter capacitor. It can get destructively loud. If you see the plates inside the power tubes start glowing cherry red, shut it down. Probably a shorted coupling capacitor or internal short and can damage the tube.
Bias the tubes per the manual.
Good Listening