[A6] power.

[MelloT at aol.com]

The history goes back to military tests in the tube/valve days,  particularly 
the US NAVY. This is the first half of the 1900's, so it's been a  while...
 
They used to run equipment for long period of time (two shifts) and "power  
down" for the last 8 hours. The tubes and some components were stressed a bit 
by  the power surge when switched on (these were "brute force" supplies, not as 
 regulated and quick to suppress surges as modern ones). Mainly, the test was 
to  determine if tube life was longer if simply left on, than if  shut down 
for 8 hours and then subjected to the "restart" surges. In their  situation, 
leaving the gear on was better for the tubes (probably NOT  for the electric 
bill!)
 
OLD story, old situation, old habit. "Old habits die hard"  - ever heard that?
 
BrianK