Effect of changing the cathode temperature on the grid potential

While exoerimenting in practice on the Pleiades Elektra III with resistors from anode to grid ranging from 1.8MΩ to 470KΩ, there is not much difference in sound. Even with 470KΩ from anode to grid the grid potential assumes the value of -200mV from the value of -400mV when Rag is 1.8MΩ. Of course when the cathode is left to cool down the grid potential grows up to that of the battery ie 12V.


Even more strange is that the sound is not much different varying the grid potential from -400mV to 400mV.


The easiest and most effective way to vary the grid potential is by changing the cathode temperature. The easiest way to do this in real time is to disconnect the heater circuit and monitor the grid potential with respect to cathode and listening to music at the same time.


Or connecting a variable power wire wound potentiometer in series with the heaters.


Setup, signal path:


Portable Sony CD player with line out - Pleiades Ekektra III - Sennheiser HD580


There is something very nice about the Pleiades Elektra III.


Is it the sweetest sounding amplifier on the planet?


Each Channel is using only 1 resistor, 1 capacitor, 1 electron tube, 1 coil (the voice coil of the headphones themselves)


Increasing the anode voltage to 18V from 12V did not necessarily produce a better sound.


Decreasing the Rag did not nessasarily produce a better sound.


The above 2 variations could be combined.


For the time being the amplifier will be as chance let with 12V power supply and 1.6MΩ from anode to grid to free the electrons.