Highest BUILD quality tube amps?

Also, Audio research can repair any product it’s ever made

But their build quality is kind of standard level. Aside from the knobs. I mean, it's not bad, but the choice of tubes and caps and circuit accounts for 100% of the sound of that gear. It's just basic sheet metal bent and silk screened with a nice front panel on it.

I'm not saying it's bad, but I wouldn't rate it at the top of construction and attention to detail. I'd rather call it perfectly utilitarian construction.

As for the sound quality, that is another story.

Speaking from personal experience alone, Atma-Sphere, Music Reference, Jadis, and AVA (Audio By Van Alstine) are excellent. Audio Research not so much, but that company may have more happy owners than all the above combined, so what do I know? Are they still mounting output tube sockets on their circuit boards? Not a good idea. The VTL retailer I know and his customers are very happy with that company’s products.

From my experience -

Audio Research line stages will generally run for close to 20 years after which the power supply caps may reduce reliability. (LS25Mk1 Ref2Mk1 LS26)

The power amps require some bravery though. (VT100Mk1 Ref110) However both are still running.

Allnic. I have 2 pieces, very nice and reliable.