Extend the useful life of those precious tubes: use a Tube Amplifier High-Voltage Delay
Tube life can be extended if you delay the application of high voltage until after the heaters have warmed up and current can flow. This little module does just that: depending on the setting of a jumper, it delays the high-voltage for 40 or 60 seconds after the amplifier is switched on. And the module is available as a kit. This article was originally published in audioXpress, February 2014.