For readers who need high continuous voltages, a low current power supply can be built with few components. The described power supply supplies up to 150 V in the 110 V network and up to 300 V in the 220 V network. The current, however, should not exceed a few tens of milliamps. Low power tube transmitters and other similar circuits can be powered from this source. However, we note that it is not isolated from the power grid, so precautions should be taken against accidental shocks. The diode should be 1N4004 if the grid is 110 V or 1N4007 if the grid is 220 V. The filter capacitor can have values between 4.7uF and 50uF with working voltages of at least 200 V if the network is 110 V and at least 300 V if the network is 220 V. The 4.7 k ohms resistors must have dissipation at least 2 W. To use, check the voltages obtained at each terminal with the multimeter, writing them down, as they may vary considerably depending on the component tolerances. If, when connecting a circuit, there is a marked voltage drop, it is a sign that the current drained by that circuit is greater than that the source can supply. In some cases, this problem can be compensated by connecting the equipment to a terminal that provides a higher voltage. Do not touch any point of the source or the powered device when in operation, as the source is not isolated and may cause dangerous shocks. If you want to have insulation for greater security, you can use a transformer for this purpose.
