Why does it take so many hours to brea in arc preamps and amps?

anybody can build their own gear

anybody can read a textbook on cognitive psychology too (well, ok not everybody...)

I agree it would be hard to measure a change - tho one could arrange a blind listening test to show an effect w/o knowing any mechanistic reason for the effect
but...
if ARC says to do something, why not do it?

for my ARC pre-amp it warms up for about 40 seconds - could be tube protection tho, not SQ

Having two ARC pre in two different systems, one bought new (17es) and one bought used (LS 27) but with only 200 hours on it when I received it, both with factory papers and both showed a recommended 600 hour break-in.

While the LS 17 does not have a hour counter, it is well over two years now so I would venture that is is well over the 600, and as noted by others, the pre started to open up becoming more defined as the hours mounted. The 27 has just started to increase soundstage (everything else remaining constant) and a slightly annoying high end has smoothed out.

I understand some of the theory, superstition and black magic behind this need for 600 hours, but if we accept the same for interconnects, speaker cables and ac power cables why not tube equipment? I regularly start up everything early in the day and do not attempt to listen until much later allowing everything to settle in producing background music as I go about my day. I have never been dissapointed at the end of the day when I really want to listen to some music...just my .02

Maybe so it's too late to return it?