[squinancy]

As an amateur enthusiast who will probably never graduate further may I add my less professional take on this. I sometimes find it hard to replace electrolytic capacitors, the inevitable main culprits. The usual values, 47 + 47 uF, or 100 + 100 uF are often difficult to obtain in the necessary working voltage, 350 - 450 DC. Single Plessey capacitors often fetch a small fortune on eBay. Paper capacitors must also, as a rule, be replaced, but plastic foil caps that do the trick are much easier to come by. Maplin does the whole range. Carbon resistors are replaced with similar ease. As for the electrolyitics, I do not find capacitance meters useless. Sometimes a choice has to be made between a cap from a dodgy source but dated let's say 1989, and a cap made by Plessey in 1965. I always test these, and choose the one which produces the reading closest to the nominal value and which shows the better retention of a DC charge. The latter is a simple test.
Gerry Wells keeps telling me that valves never go wrong. While that is an exaggeration, problems posed by valves are straight issues. I always replace valves which appear not to perform according to specifications. Sometimes this is a costly policy.
Maplin has a 48W digitally controlled heat soldering iron for 30 quid, great value I think. This is what comes to mind in brief. And best of luck.