It’s a very nice, warm, full-tone preamplifier. The soul of the circuit is two BC109 transistors. These are old, well-proven types. Interestingly, the base of transistor T2 is connected to collector T1. This is called direct coupling, and the signal is transmitted between stages without attenuation. This means that there is no capacitor, resistor or transformer between the two transistors. This makes it less repressive to the guitar signal. This circuit does not distort, that is, only when the guitar volume is at its maximum.
This is the first version:
In this video it works on 9v voltage, see: