My stereo has had various components replaced over the years; speakers, CD players, cassette decks, record decks, tuners. One part has remained in use for 30 years - the amplifier. It is one I built and is an E.A Rule design called the PW Winton, that featured in the March 1979 issue of Practical Wireless. I have only had to repair it once when a coupling capacitor dried out and went noisy. A very reliable amp, thanks mainly to the output stage using complimentary Hitachi power MOSFETS (2SJ48 and 2SK133).These devices have a negative temperature coefficient so there is no risk of thermal runaway. When I get time I will scan the article and put it online.