Extending tube life with a HV 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. It can easily be retrofitted to any amplifier because it is wired in between ground and the power transformer center tap (or between ground and the bridge in a full-wave rectifier). It needs a floating heater winding or equivalent to power it. You can read the full article here, courtesy AudioXpress.
Update May 2019
I am in the process of publishing an improved version of this. This new board does no longer need a heater winding for power (it is self-powered) and lets you set the delay between 20 seconds and 254 seconds. Stay tuned!