What they should have said is that two of the cathodes share a common connection, there's three cathodes in the valve, each one heated by its own heater, the three separate heaters are series connected in the valve.
Two of the cathodes have to share a common connection because there are only 9 pins available in total for all the electrodes and heaters.
The way the valve is graphically represented in the Philips valve data sheet sums it all up.
The audio output is via the tertiery winding and R20/R22.
Lawrence.
Two of the cathodes have to share a common connection because there are only 9 pins available in total for all the electrodes and heaters.
The way the valve is graphically represented in the Philips valve data sheet sums it all up.
The audio output is via the tertiery winding and R20/R22.
Lawrence.
