Found in the May 1971 Radio Electronics magazine, this is the circuit for a commercial high-impedance instrument. The circuit uses 4 transistors and is powered by 2 9 V batteries.
The oscillator shown in the figure generates a rectangular signal with a 50% active cycle (square)...
This power supply can be implemented with a TIP32 providing an adjustable output at the 2k2...
This switched circuit was found in an old documentation and no information about the transformer...