amplifier longevity

Heat, depending on design and how and where is used, can defiantly pose a longevity problem.

Early model Krell KSA and KST power amps notoriously failed do to cap failure from heat. Design modifications using better caps and more attention to heat dispersion solved the problem. I know of the problem with the Krells because I had them and went through the headache and expense of getting problem solved.

Not to pick on Krell, per say, as am sure that other early hi-biasing class A/AB amp manufactures had heat issues to work out as well......Jim

Like @rbyington711 said, Pass Labs, particularly X350.5. They are built like s tank and sound like top-notch tube amps. Their electrolytic capacitors are lasting >20 years. I went from Pass X250.5>X250.8>X350.5. Each time I am amazed how good they sound.

@bigkidz I beg to differ. Keystone makes those white Q Covers with 4 holes, 1 hole, and no hole. The holes are not for ventilation but for a tech to use a probe to check rails voltage. There is no difference in temp disspation between the convention black Q Covers and the Keystone nylon ones. Any amp with a design where there’s more than 10-15V on the TO3 case should have Q covers covering the whole component for safety reason. The SA220s have 65+/- rails and they give the curious owners a good zap once in a while if not covered. The nylon keystone covers expose 2 screws... I honestly would not recommend unless you are using them to cover filament regs like 7806 or 7812s.  There is a reason why the black ones are still being used and sold for output devices.

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Any amp with a design where there’s more than 10-15V on the TO3 case should have Q covers covering the whole component for safety reason.
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I know testing a 9V battery with the KISS method of the wagging tongue, is about as much as I like. More volts would taste worse.