The cathode current is only 0.15 mA, but the preamplifier delivers a 3.5x gain. There is more detail on his website. It would be interesting to subject this circuit to a full audio analysis and ...

A glance at any outlet through which Chinese modules can be bought will find this type of tube in small audio amplifier ... all remarkable about the preamplifier circuit. The 6J2 is wired as ...