Capacitors: Characteristics, Series, Parallel, limits, etc

If you wanted the standby switch, use a DPDT switch, and connect the B+ to a resistor sized just enough to bring the voltages to a safe level, without excessive dissipation.A small cap is needed across the switch terminals for arc suppression.
 
If you wanted the standby switch, use a DPDT switch, and connect the B+ to a resistor sized just enough to bring the voltages to a safe level, without excessive dissipation.A small cap is needed across the switch terminals for arc suppression.
My MFA M75 monoblock, PP kt88 , amps have standby switch, as they are SSR. The switch is a big toggle with a cap across the terminals. I would let the amp warm up about 5 minutes and switched it on. Never had problems with the power tubes.
In the circuit you mention with the resistor, how will the switch be wired with the components?
 
When a tube is run with little to no current it forms orthosilicates. The bias current is low and the reaction still occurs. Trickle will slow the process but will not stop it.

You seem to be saying that when there is no audio signal, the tube is passing "little to no current," or just a "trickle." This is really not true. The quiescent current in the output tubes of a typical push-pull amplifier is a lot more than "a trickle." It is typically enough to represent a significant fraction of the tube's maximum power dissipation.

The other tubes in the amplifier, like the driver stage, will be operating in class A and so their quiescent plate current when there is no audio signal will be more or less the same as the average plate current when there is a signal.

Of course, if the amplifier is single-ended, then the output tube is operating in class A, and so the average plate current is hardly dependent at all on whether there is an audio signal or not.
 
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I'm thinking something like this, but there would be quite a thump when switched.
Another possibility would to disconnect the cathode of the output tube, and switch in a resistor to ground after the choke
Maybe a third option would be to put a resistor between the 5Y3 and choke, bypassed with a switch, the resistor value dropping the voltage to ~1/3 so as not to pass signal.
 
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