If you had a protege you wanted to get to pass the Extra, would you give him something like this, or have him assemble kits off Ebay?
1) You don't need any technical skill or electronics experience to make Extra. Read the forums here and you'll see what I mean. In your case passing one written test is all you lack and there are plenty of study materials and practice tests to be found on the web. You have no excuse for not making Extra.
2) While the repair & rebuilding of an older transceiver requires some comprehension of electrical theory, R & R of a distressed radio is not essential to learning theory. Depending on the issues with radio, it's entirely possible to troubleshoot with nothing more than a free downloaded schematic and a free multimeter from Harbor Freight. Then you'll have a better idea of what kind of money it will take to get it working, working well, or working better than new. Not every refurb needs to be a complete top-to-bottom exercise nor is every radio worth the time and expense of a workbench Full Monty.
It's like the old joke...
What do you call the person who graduates at the top of their class in med school? Magna Cum Laude.
What do you call the person who graduates at the bottom of their class in med school?
Either way they can spend the rest of their life asking people to take their clothes off and charging for it.If you want to learn theory from square one here's a place to start
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Once you learn the concepts of energy flow and the function of various components, then you'll learn how a radio can have independent AC and DC circuit paths on the same wiring as determined by the placement of a blocking condenser or choke... DC can't flow through a condenser and RF might not flow thorough a coil if, like N4NYY, it's wound too tight. Then you learn the various sub-sections of a radio like amplifiers, mixers, detectors, etc. and how they work together.
There is more than one way to learn this stuff and just because an Elmer learned via junk radios and magazines doesn't mean everyone has to learn the same way. Do you realize you can pick up old clock radios & such at a thrift shop on the cheap and strip them for parts? Like, enough parts to build a crystal radio with a simple audio amplifier. In fact... If you want a first project, score an orphan clock radio that has a transformer power supply (a transformer means the chassis isn't hot relative to ground) then add a switch & phono plug so it can be used as a radio or test bench audio amplifier / signal tracer. Plus, you get a digital clock at no extra charge. Then learn how to build a demodulator probe so you can 'listen' to an IF strip.
It doesn't take much money to do this and a signal tracer is a useful tool......................