This is pretty common, not specific to Diezel but just tube amps in general.
In the future I would recommend to you or any tube amp owner to keep a spare set of power tubes and fuses, as well as a preamp tube or two and a screwdriver around. You don't have to be a hardcore technical guy and you can save a lot of money and time by just learning to identify a bad tube and fuse yourself instead of taking it to a tech. That said every time I've blown a power tube, it's been more obvious than your pictures. The hard ones to troubleshoot are where it looks visually OK. The same applies to fuses, your sample fuse is clearly blown, but I've had fuses blow that still look good - but touch a multimeter to either end and the continuity is broken anyway.
Same logic behind telling people they should learn to do basic setups on their guitars. It always blows my mind when I hear someone took their floyd-equipped guitar to a tech just to change tunings. It's just a few twists of a screwdriver, but the tech is probably going to charge you for a full hour to do that for you.
