The VF14 in a U47 only has 34 volts at the anode , yet 36v at the cathode, I dont understand how the anode can be less positive than the cathode and still attract electrons .
VF14 spec sheet shows 200 volts max at the anode, so its massively undervolted in the U47. I read a few mentions of undervoting heaters while starvtion conditions at the anode , it does seem to make sense as the less high the anode voltage the less it attracts emission from the cathode the less electrons you need there ,
Heres a quote from the Phaedrus audio site ,
The VF14M valve acts as a voltage amplifier circuit and drives the output transformer which drops most of the voltage gain of the valve, but translates the output impedance to drive the long microphone cable. As explained above, there is only one supply which is used for the HT and for the heater supply for the valve (under-run in this application at about 35V). The heater supply is simply dropped by the 1800Ω resistor which dissipates about 2.6 watts in the process.
The VF14 valve is strapped as a triode, with the additional, unusual feature that the suppressor grid is strapped to the anode, rather than the more usual cathode. More unusual still, the valve is operated with a very low anode voltage (circa 35V).
These conditions are well outside the normal operating and design envelope of the VF14 device and, in the majority of cases, this anode voltage is not enough to pull the valve out of grid-current. (This, along with low-noise and lack of microphony, was one of the principal conditions of the Neumann selection.) This also explains why the valves are operated at 63% of their specified heater voltage. By reducing the temperature of the cathode, the emitted electrons have a lower statistical kinetic-energy and the available space-charge of electrons is shrunk to that required to sustain the modest anode current. In this way, there are less electrons “all charged up with nowhere to go” which could contribute to a grid current.