How can I learn how to fix equipment

Buy a pile of broken stuff.
Rip it apart and see if you can fix it!
Get some basic books and tools.
If you have NEVER done anything like this already, you should think twice about this.
(unless you are under 21 years old.)

Radio Shack makes some very nice experimentation kits that consist of a breadboard and instructions to make some basic circuits like a light sensitive bell. You can remove the components and reconfigure them to make a few different things. There is a book that goes with the kit that will teach you all of the basics that you need to know about electricity, capacitors, resistors, transistors, etc. You may want to invest in a basic book about electronics as well. Of course, none of this will address vacuum tube design, after you have mastered the basics, get yourself a copy of one of the RCA receiving tube manuals. I assure you, if you read it cover to cover, you will know more than most of the self-appointed tube gurus.

If you're "handy" with electrical/mechanical stuff I would say you can teach yourself. By handy, I mean you generally have an aptitude for diagnosing problems with mechanical/electrical stuff, disassembling/reassembling, soldering, etc.
There are books on electrical circuits, repairing electronics, building, and testing electroni circuits that you'll need to read. I suggest your FIRST read about safety with electonic devices before you stick your hand inside one - they can get you even when unplugged. Then do as Elizabeth says - get a bunch of broken stuff and go to work.

The only thing I would say is that getting to be able to fix simple, obvious stuff is easy, being able to diagnose a problem with a complex circuit is a lot more difficult. You also need tools and test equipment, which you need to learn how to use.