How does a preamp die from sitting unused for a few months?

By checking the fuse did you do a visual inspection or did you do a continuity test with a multi-meter? A fuse may look fine but can be broken inside. If you don’t have a DMM replace the fuse and try again.

If that doesn’t work then maybe the power cord is not reaching the connector’s pins. To test this you need DMM. Put in a good fuse, open the bottom plate of the amp, plug in the female cord to the amp’s inlet receptacle (leave the other plug end unconnected from a wall outlet) and test for continuity between the cord’s hot plug and both tabs of the fuse holder. If there is continuity through the plug to the fuse holder tabs then the problem is inside, which definitely requires a service from the factory .

I'm guessing danager is probably right.  😉

I only visually checked the fuse and didn't do a continuity test with the power cord connector.  I'll try those next.

None of the tubes turn on.  I'm leaning toward the toggle power switch gave out as there is nothing remotely loose or broken off inside.  DHad does some great work!

If the rectifier tube is burned out would the rest of the tubes and power indicator light light up, or would all electricity be stopped at the first tube (here I'm assuming the rectifier is the first tube)?

Thanks, all.

+1 @gs5556  .  Always ohm the fuse out.

I'm guessing the power switch or the rectifier.  If there is a big capacitive element in the power supply there can be a pretty severe shock to the system when first turned on.

My Lab12 Integre blew its fuse twice already, and I can assure you when I took out the damaged fuses there was no visual indication whatsoever on the damaged fuses. That's why it's handy to keep spare fuses around.