Leaving tube amps on.

Don Sachs had addressed this subject, some time ago. If I remember correctly, he had suggested that it is good to turn the tube gear off, when not listening.

I was first introduced to Valve Equipment in the early/mid' 90's and was quick to move over to the schematics using Valves in place of Transistors and Semi Conductors.

I had my first Valve Amp' Pre and Power commission built, and the EE who at this time had a good few years of working with Valves to produce Audio and Studio Equipment gave me as a newbie a clear warning.

Valve Equipment is not a Turn On and Forget device.

Valves in use need monitoring during use and after Power Off.

I have kept to my side of the Bargain for the best part of 30 Years and see no need to make a change. The same EE remains a friend and has produced further Power Amp commission builds for me. 

Red Plate is common on a Output Valve and is a result of incorrect Bias, where increased Voltage is enabled.

Everything in Valve Talk is about reliability, maintained Bias is extremely important.    

@pindac Thank you for clarity on Red plate. I was just gonna ask how important tube bias is and what can happen if not biased. 

@tattooedtrackman  , on bias and red plating,

a few years ago (I think it may have been some time in '20, I had a coupling cap fail on one side of my Cary V12..  I won't try to explain the science or theory of whatever happened within the circuit, because that kind of stuff is beyond me, but the result that I saw was the bias on that side running away high regardless of the position of the bias pot.  (I could back the bias pot all the way off, but shortly after turning the amp 'on' the bias would start climbing out of control on that side.  The tubes on that side got very hot--red plated--and were never the same sounding after I replaced the cap.  I felt the tubes were getting tired anyway, but that event was the last straw and I bought new tubes.  

@tattooedtrackman A number of years ago I bought a preowned tube amp that according to the manual to set the bias you had to put a tiny phillips head screwdriver in a tiny hole until you blindly felt the phillips head screwdriver engage into the phillips head bias screw.  Then turn the screw until the amp shows proper bias for that channel.  Unknown to myself the previous owner had had a bias pot replaced with one with a normal slotted screw.

Well first time biasing I broke off some part of the bias pot and a second later.  I was met with smoke, smell and a real fireworks show. I hit the on/off button and that did nothing to stop what was happening.  I then pulled the plug and the show was over.

If you really saw and smelled what occurs when something like this happens you would not even want to think of leaving your tube amps on and unattended for a long period of time.

Surprisingly the cost to repair the amp was minimal.