Do vintage output power tubes - Mullard, Amperex, Telefunken etc - ever red-plate ?

@inna 

A tube can red plate for a variety of reasons, none of them having to do with vintage or new production. 

Bad connection on the tube socket, damaged grid stopping resistor, open bias circuit, failed connection in the base of the tube itself, internal short or leakage in the tube. 

I , of course, meant that some vintage tubes might be of such quality that if they ever red-plate it is not because of their failure but because there is something wrong with the amp, and when they do eventually fail they do it differently, not red-plating and exploding.

I understand, most often red-plating happens right after you turn the amp on, though it can happen at any moment.

Very recently my friend of 30+ Years, who is also an EE of longer years and is my  Tube EE, was doing a spruce up to a Amp' brought in for a little TLC rejuvenation.

The Amp' is quite well known in the UK and has no horror stories associated with it. This same Amp' ignited when undergoing added parts reliability testing.

My EE has always strongly suggested the Tube Amp or Tube device are always with a eyes on them when the power is Power On.

I have followed this advice for 30+ Years and have no horror stories to tell.

I have had a few Horror Valves that proved to be totally awful. 

When red-plating happens, how many seconds do you usually have to turn the power off before meltdown event ?