So I have a laney tt50 head running through a crate cabinet and I just replaced a broken fuse in it. I turn it on and everything lights up like it should and my clean and 2nd channel's are working but when I go to the 3rd channel(lead), no sound comes out.
Did you put the right fuse in it? Why did the fuse blow(assuming it blew) in the first place? Did you address the issue of why it blew?
Check all your valves are heating up.
Yes the right fuse is in place, and all valves are heating up.
You never just replace a fuse. Fuses don't just blow for no reason - they are there to stop the flow of electricity to certain components when something goes wrong so things don't get ruined. If a fuse blows, take it to a tech if you're not knowledgeable on the innards of your amp.
Can anyone tell me why my third channel isn't working though. I know what fuses do, its just I know why it was blown and how it happenned.
Read the above posts, the fuse blew to prevent damage. You replaced the fuse and turned your amp back on, possibly causing further damage. Your third channel doesn't work as something in your amp is broken.