In 1980 I bought a Yamaha M2 Poweramp 240 w. Of channel weighs 70 lb. To purchase a 240 w amp today that's built as well as this one would cost me $5 to $6,000 or more. This amp was sold by Yamaha is a high-end home amp and also as a power amp for PA systems and concerts. I had a local tech that specializes in '70s and '80s amps only take it apart. Change relays that had corroded contacts because it had relay protection in several areas. Cleaned all the pots. Checked every capacitor. Checked all all transistors for proper specifications. All the parts that are inside these amps are subject to changing their specifications over time because of heat abuse, high voltage, low voltage spikes, whatever we're talking thousands of parts in these amps. Yes they will run perfectly for years and years and years. But if you want it to run like it was from the factory going through and and replacing the Hi-Spec parts that Yamaha put in with the high spec parts that are available today is the cheapest thing you can do. In the end I put $750 into the amp that I bought for $1,000 and it still is better than a $5,000 amp today. The amp is such a sweet piece of equipment. I purchased a second one because I'm going to buy at my speakers cost me a little more cuz it was having a problem when I got it. But now it sounds just as sweet.
Yamaha is one of those engineering companies that just likes to do things top notch when they're selling a top-notch piece. If you look at their current offerings they have three levels of basically the same power amp. They're all supposed to be 100 w a channel but the quality of the construction as you move up becomes apparent as to why some of these ultra expensive amps do Excel at their craft. I've been an audiophile since 1975 and I've watched the industry grow up. I've been watching these companies grow up and it's always the company that goes to the nth degrant engineering that'll last today's modern high-end amplifiers are very well built. Use quality components. My choice is for the vintage because they just look cool. Enjoy whatever you have and enjoy upgrading it