Why did my amp just crash and burn ?

itsjustme is correct turn it off. I’m still guilty of changing out interconnects as long as I change the source.  Most of my amps are tube and I don’t want to wait to turn it back on. I’ve learned to turn amp off when playing with speaker wires I double, triple even quadruple check speaker wire before turning amp back on. I had to learn the hard way when I blew up the McCormack. 

You may have grounded positive speaker wire to chassis while handling speaker cables. Like someone said open up the amp look for more fuses. Look for burnt resistor, black marks on the board, look at power supply electrolytic caps usually the tops where the cross is are swollen, even swollen film caps. Look at it as a learning experience what not to do, that’s what I had to do, Good luck.

Nice to see you all trying to help.

If the amp was on and the speaker cables not tight you created an ever load of resistance to the circuit ,check the fuses first ,sometimes you get lucky see outside fuses, and inside with a volt meter  pull each one out while unit s Unplugged .

We all make mistakes ,Always make sure all cables are secured good before turning the unit on Even swapping a digital usb cable I turn everything off  first.

It doesnot take much to cause a spike or surge , that is most likely  what happene. 

Well, was the main fuse blown.

If not , then there is a other issue. Do not attempt to fix it yourself.

Just getting the chassis open is difficult, and there's nothing you can repair yourself unless you are experienced in such things.

I have some news for everyone. So, I got home and turned off the amp and all other components in the chain. Next, located the fuse drawer on the back and could not get it to open with a flat head screwdriver. Easier to just unscrew the two screws attaching the socket to the chassis. Finally got the drawer open from there. Inside there was what looked like a frazzled 6amp fuse and next to it in a small storage compartment was a spare fuse. Inserted the new one . Went ahead and connected all ICs and the new speaker cables to the amp. Moment of truth. Connect the power plug , turn on the power button. Life is back in the amp. Life is good again .

Lessons learned : Never work on installing cables in particular spade connections with power on . Ensure spades are fastened tight enough to ensure non contact now or in the future. Never rush the process. 

All worked out well. Much praise to all who contributed along the way. A great show of support I would like to reciprocate to beginner questions in the future.