Tube power supply with low-voltage transformers
For the construction of tube devices, the required power transformers are usually not easy to obtain. But there is the possibility to win the anode voltage with two low-voltage transformers. Of these, the second transformer is connected in reverse, i.e. it transforms the low voltage again high. As a rule of thumb, the second transformer should have about half the power of the first one. This leaves enough reserve for the heating power, because it makes sense to use transformers, which are designed for the value of the heating voltage. A value of 6 volts is within tolerance for E-tubes (6.3 volts heating voltage).
If e.g., for receiver or preamplifier circuits, a lower anode voltage is needed, the second transformer may be designed for a by the corresponding factor higher secondary voltage (e.g., 9 volts instead of 6 volts). It should be noted that the anode voltagewithout load almost reaches the peak value of the AC voltage, so at 230 volts, well above 300 volts. If a selenium rectifier is used instead of the diodes, here this value is again significantly reduced by the voltage drop.
I would like to point out that experiments on mains voltage should be made only by qualified persons!