I've got an issue with my Sovtek Mig 50 head, need some help from someone who knows electronics. I snagged the Mig off of eBay a few months ago, worked great when I got it, and I retubed it and biased with a matching set of Sovtek 5881 power tubes, and Sovtek 12AX7 preamp tubes to make sure it was in top working/sounding condition. The amp worked great for a month and I gigged with it last weekend, and it sat in its case all week. Went to play it today only to find that it wouldn't turn on. Checked the fuses, and the main one seemed to have blow. It looked like it was the original fuse, so I got a package of replacements, went to power up, indicator turned on and it buzzed for a few seconds before shutting off with the replacement fuse blown. I haven't replaced it with another fuse as I don't want to damage the amp. Could it be a bad power tube? At the moment I really don't have the money to take it to a tech, so I'm wondering if anyone else has encountered and fixed a similar issue.

Much gratitude to anyone who can help me out here.
70% chance it's a bad power tube, 30% it's broken. If you're skint right now, you'll just have to wait until you're not.

Try taking out and reseating the power valves, if it still blows get it to a tech. It probably just needs new tubes but they'll need biasing anyway.
Tried pulling the tubes, and unfortunately it's a 30%. Gotta save my pennies here, I need it for another gig in a few weeks.