Highest BUILD quality tube amps?

+1 for Music Reference tube amps. Roger really knows what he's doing. The amps I have appear to be bullet-proof...

i haven't seen a mention of Cary.   Mine are going on 9 years old and not a single issue.  Had the pre=-amp modified to accomodate HT bypass and that was carried out flawlessly and supports attention was top notch.   My close friend has Cary also about the same age again no issues.   And of course there is the sweet Cary sound.

Really enjoy the sound and build quality of Linear Tube Audio (LTA) equipment built in Tacoma Park, MD. The equipment features David Berning's Zero hysteresis Output Transformer-Less patented technology (ZOTL). As well, it is always a pleasure to talk with, learn from and discuss high fidelity with owner Mark Schneider. In my over 50 years as an audiophile, LTA was the first tube equipment I ever bought. The LTA equipment is purely about music without thought of is it solid-state or tube.

Coincident Speaker Technology, my 300b Frankenstein mono's are PTP wired and have been trouble free for many years.

I own both a Cary SLI-80 and an Ayon Audio Spirit III.
IMHO, Ayon is far far superior in build quality (for twice the price at new retail, so you’d expect that).
The Cary’s volume pot has become loose over time, and so has the power switch, and the original remote is starting to fail.
The Ayon has the additional benefit of tube auto-biasing and comprehensive startup/shutdown sequences that extend tube life. And it is a far more controlled and prcise sound than the Cary (which is still very pleasant when not making direct side by side comparison)
That said, the Ayon remote is a super solid shell of heavy aluminum, but the soldering of the board to the battery holder is weak and almost impossible to repair (I tried, failed and had to order a new remote).