Chopper for operating tube devices on 12 volts DC
In order to operate tube devices with batteries or on board of motor vehicles, the available low DC voltage must be converted into a much higher anode voltage. An AC voltage produced by a power generator can be brought to the desired value with a transformer. After subsequent rectification and smoothing, a high anode voltage is available, as is commonly required for tube circuits.
In the circuit shown, a conventional power transformer is operated in a reverse manner by feeding the working by four transistors power generator to the medium-tapped secondary winding of a conventional power transformer. Is that designed for 2 x 9 volts, builds a voltage of about 230 volts, when supplying the circuit with 12 volts on the primary winding of the transformer, so that after rectification well 300 volts are available. In the dimensioning shown, the circuit is suitable for powers up to about 50 watts. The two transistors of the type BD245 must be well cooled! The input voltage can also be used to heat tubes with a voltage of 6.3 volts when two filaments are connected in series for the same heating current (for example, 0.3A for an EF184 or ECC81).
I do not want to neglect to point out that experiments on mains voltage should only be carried out by competent persons!