What's going on in this circuit?

[old_tv_nut]

V1 and V2 heaters are DC powered from point Z.
Some peculiarites, though:
Noted voltages are 10 V DC for V2 heater and 8.5 v DC for V1 heater. Heater resistance must have been different for the two tubes actually installed.
DC at V2 pin 4 (point Z is noted as 18.5 volts, DC at V4 and V5 cathodes (also point Z) is noted as 20 volts, should be the same.

V1 and V2 nominal heater voltage should be 12.6 volts according to 12AX7 specs. (This same value should be read either by DC meter for DC heater supply or by AC rms meter for AC supply.) The lower values on the schematic caught my eye. I found some discussion here:
https://audiokarma.org/forums/index....antage.845172/