Why did my amp just crash and burn ?

learning moment: never touch any connections with the amp on, playing and connected to the speakers. You could damage the amp (maybe, most likely just a fuse) and could also, if you hit the wrong thing (say life an input ground) cause a noise transient that fries one of your speakers.  Its just bad practice.  Don't put your hand in a live socket, don't sharpern the lawnmower blade while spinning, and dont eff with your amp, interconnects or speaker cables while playing.

I find it amazing that people don't get these basics.

Now on to fixing it. I suspect what you did was short the amps outputs.  That means ti delivers X volts into zero ohms = infinite current.  Bzzzzzt.

It MUST have at least a line fuse. Hopefully sized to protect stuff beside your house. Side discussion - as a designer i see people who have partial shorts fix them by putting in a bigger fuse.  Let's not go there.

I would guess the fuse below. I would hope nothing else did.

replace the fuse WITH THE SAME AMPERAGE AND TIME CONSTANT.  BOTH MATTER.  e.g.: 3A slow blow (now often called "time delay"). or 5A fast acting. Or whatever it says on the back panel and in the manual (not necessarily what the fuse says since it could have been incorrectly replaced).

G

if yo need servicing I'm in the New Jersey NYC area.

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.