For valve amplifiers, it is said, that applying anode voltage before the valve is heated reduces lifetime and can have other negative effects on circuit lifetime.
To avoid this, I want to add a thermistor to the HT voltage line, so the valve has time to heat, and the HT is applied in a more controlled manner.
Based on what parameters of my circuit should I choose a thermistor? Or what else should I use to "delay" the HT voltage?
Currently I am using a manual switch, which is good for standby mode, but I'd prefer to have something, that doesn't rely on the human factor.
Edit: In the past this was solved by using tube rectifiers, so they would need time to heat up too, but I want to use solid-state rectification, so that is not an option.