I just bought a used 5150(not 2, 1) from Guitar Center and it has two power tubes instead of four to reduce it to 50W, which is totally fine with me. I also got a JSX cab, and a speaker cable to connect them.

When I turn the head on, there is very little volume to the point of where I can barely hear it. When I connected it to the cab, it was horribly feedbacky and sounded way too loud.

Can I get some help on how to reduce that and control the volume better?
Turn the master volume to zero and then slowly increase it?

And NEVER turn on the amp head without it connected to the cab and then start playing through it. Seriously, that's really really bad for it. You can blow the valves and all sorts doing that!
Alright I'll remember all of that. I think I got it figured out now.

Thanks guys!