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. The small PCB and the control chip that takes care of the delay can be had from Circuit Cellar's online store. You can read the full article here, courtesy AudioXpress.
The PCB and controller chip are no longer available on-line but you can have your own PCBs manufactured or organise a Group Buy is you wish. The Gerber files are here and should be useable by any reputed board house. The Hex file for the controller firmware can be downloaded here.