Power Amplifier Longevity

The quality of the capacitors used can have a big effect on the longevity. Cheaper caps are maybe 20 years or so (I call it a 'half life' but what I mean by that is half of them that old have failed by that time). Better quality means that your half life is more like 30 years. So it is prudent to consider filter cap replacement in any electronics if they are older than 30 years! 

I know nothing about electronics, but a couple of months ago I gave the Sony AV receiver I bought new in 1991 to my nephew to use, along with similar vintage Jensen speakers rated at 8 ohms.  Before I gave it to him, I looked inside and cleaned it up a bit, and the filter capacitors looked fine (not swollen or leaky), as did the circuit boards (not dark or burnt-looking).  I found the sound to be pretty good, for what it is.  But from reading here, it sounds like a receiver that old likely has capacitors (and perhaps other parts) on the way out, and when that happens the speakers are probably going to be damaged too.  Unless one does their own repairs, does it make sense to repair something like that when it does go out?  So, use it at your own risk and throw it away when it blows?

@jollygreenaudiophile...

I guess you did not read the last part of my comment mentioning Pass Labs amps. Please read it again :-)

As for inrush current limiters, MOST devices sold today do **NOT** have such current limiters. Also, I am not quite sure how you got "fuses" lumped into the same category as a current limiting device but there is absolutely no correlation between them.

Any device which uses transformers (especially toroidals over a few hundred VAs), and electrolytic capacitors (such as the large filters on most power amps) present an almost SHORT CIRCUIT to the mains within the first cycle of the AC voltage, which lasts about 1/120th of a second. This is a very long time in the electronics world. Until the magnetic field is established on the transformer, the ONLY limit is the simple PURE wire resistance of the transformer. This can be in the very low ohms for large transformers (1 or 2 ohms max). We are talking in excess of 80 - 100 amps of inrush for 1/60th of a second. That is why lights dim for a second when some amps are switched on. In addition, on the transformer secondary side, the filter caps are a also virtual SHORT CIRCUIT as soon as power is applied. This means your rectifier is presented with a short circuit as soon as power is switched on. Again we are talking 100s of amps instantaneously until the caps start charging. Those currents, despite being on only about tenths of a second present a tremendous overload to the components, especially the rectifier and the capacitor itself.

Check out the circuit here from Nelson himself:
https://www.diyaudio.com/forums/diyaudio-com-articles/154777-burning-amplifier-ba-1-a.html

The items marked as THx (resistors with arrows thru them) are called Thermistors or NTCs (Negative temperature coefficient) meaning their resistance DROPS as temp INCREASES. Their purpose is to limit the inrush current.

Few commercial amps employ them as of today.

The point about doubling the voltage on components is simply for over-engineering. There is NEVER any harm in doing it except simply their expense. In addition, higher voltage capacitors have MUCH HIGHER ripple current ratings (check out digikey and search for them, look for low frequency ripple current ratings and ESR) which in the long run always make the components more reliable and less prone to spikes.

These things ALL add up, bit by bit, and increase the lifetime of an amp to 30 years from maybe 15....