To experiment with tubes, a power supply that creates higher voltages is required. Most lab power supplies supply up to 30, maybe 50 volts, some older ones may even go up to 100 volts.
While tubes operate already somehow at these values, for testing etc., I looked for a real tube power suppy.
I found one from an older german company, called NEVA. As far as I can see, they mostly produced for universities and school labs. The power supply is older and looks like being produced in late 70ies or early 80ies.
It offers 6.3 volts with 3 ampere for heating . An adjustable plate supply voltage from 0..+250 volts at 15mA and an adjustable gate voltage 0..-50 volts at 15mA. It also offers an unregulated plate voltage of 300 volts, then at 100mA.
This was for 220 volts regulary input supply, today we have 230 volts, so the real output is higher. The fixed plate output is about 380 volts and the adjustable output maximum is about 370 volts (with a single tube as load).
Build quality is high. The technology of power supply is simple. Just rectifier, caps and resistors.