Deluded or daft? DAC10 anomaly?

[boater sam]

The "earthy" end of the pot is connected to the shared cathode resistor of UF41 and UBC41. My DAC10 works well, but I've not checked how it's wired. If the valves are good and the grid resistors are high enough value it will work by "grid leak" bias method, the current flow creates a negative charge on the grids. You can ground a triode cathode preamp if there is maybe a 10 M Ohm grid resistor.

Obviously if your DAC10 is wired in error, it may work but the bias is wrong and gain would be low.

This is most obvious on a heptode/octode oscillator, where you can feed grid to a low pass filter (no diodes) and use the -8V approx to class AB bias a push-pull output as on the Philips Colette battery valve set.

All true but the earthy end of the pot is earthed by a link onto the pot body, effectively shorting the 2 cathodes to ground.