[Arran]

There was a series of books published by John F. Rider in the late 1950s and 60s that was based on a series of books created for the U.S Navy, one set is called "Basic Electricity" which I do not have, the other is called "Basic Electronics" which I do have. If you can find one or both of these they would be quite useful, especially for understanding tube electronics. The ARRL annuals can also be useful, as can the first section of any older RCA or G.E tube manual. Elements of Radio Servicing is very useful for actually repairing sets, there is also a companion book that deals specifically with AC/DC sets.
One thing you should learn how to use is a volt-ohm meter, you should also memorize the resistor code and know what Ohms law is for. In spite of what some think you don't really need a lot of fancy test equipment to diagnose most problems with a radio, voltage and continuity tests will find 80%+ of the faults. Unfortunately one common fault can't be found by these methods, that is someone coming along a twiddling with the assorted trimmer capacitors and slugs in the set. So for this you need a good, reliable, and calibrated signal generator, unfortunately the typical two tube EICO and Heathkits jobs you see everywhere for sale are not, at least not without a rebuild.
Regards
Arran