Bear in mind that back in the golden age of tubes, tubes mattered, their reliable operation was essential to the continuation of the free world and civilisation as we know it
And similarly with the 'unfree' world
The military industrial complex on both sides committed massive resource into getting tubes and their application developed to the point we're familiar with.
Consider that if a 'standby enabled an extended warm-up and cool-down' would have helped to ensure that, eg a 5881 drove the servo to open the B52 bomb door or whatever, then guidance to that effect would have been included in the manufacturer's information, and Tomer would have mentioned it in his exhaustive report linked to previously.
How can g1, g2 or g3/beam plates short to the heater? Apart from a bit sticking out at the end, the heater structure is encased in the cathode.
And amps would normally be turned off whilst idling, when grid dissipations are minimal.
eg a 6L6GC g2 limit is 5W, whereas it may idle typically below 1 watt.
Sure but my guess is that may be due to incompetent standby implementations, eg http://schems.com/schematicheaven.net/m ... w_100w.pdf or just from designs that subject tubes to operating points that are beyond their limiting values.
All this is your hypothesis, right? There seems no way you could ascertain that a previously functioning tube has failed as it cools?Stevem wrote: ↑Sun Mar 11, 2018 11:21 am...In this type of failure the tube has already shorted out when the amp was turned off. The last time it was shut down , not when we just turned it on, and to me this a mechanical failure from the cycle extreme of hot and cold which a standby switch can help to ease!...