Experiments in Low Voltage Tube Audio Amplifier Circuits

We can very easily design RIAA phono and line preamplifier circuits with solid state devices such as FETs, ICs, and transistors with low voltages in the +/- 22 volt power supply range. Most commercially manufactured tube preamps however have power supplies of several 100 volts. In this article, Ronald Quan shows that phono and line preamps can be designed with low plate/anode voltages of around 45VDC, using commonly available tubes, while providing good performance. The author discusses some of the challenges in low voltage design, which are not an issue when high voltages are available. All presented designs can be supplied from a common 48V ‘wall wart’.