In relation to DIY Hybrid amplifer the first step is to obtain the High Voltage for tube's anode supply and the low voltage for heaters.
Sometimes, if not always, fora a 100W amplifier you have a double sec 150-300VA 36-0-36Vac power transformer only.
Using this board you can adjust the needed voltage for tube stage starting from your transformer.
Without use any voltage doubler and linear regulators.
The Following image shows how the Double Boost works.
From unregulated +55/0/-55Vdc the circuit gives at his output the needed voltage, able to supply the anode current for a tube stage.
For example you can obtain +90/0/-90Vdc and 6.3Vdc for the heaters..