It is very important to delay the high tension to come in if you want to save the live of your electrolytic caps and the power tubes. There are many circuits in the market, most of them using solid state. This is one with a tube. It has the benefits of the memory of the heater of the tube. If the mains is interrupted only for a sec or two, it switches h.t. on immediately. If the tube is cold it takes as long as it takes to heat it up. I don't know what you have in your junkbox so you have to experiment yourself on the exact values. The resistor in the heater circuit mentioned below is to make the tube heat up a little slower then the other tubes rather then to lower the tension. If your power transformer has connections for fixed bias that you don't use for that purpose try those for this purpose.