Jim Mueller wrote:
Why remove the pins you don't need? The only thing on that end of the
tube is the filament and if any of the pins are used as tie points they
better be at filament potential. The voltage is high enough to jump to
any pin that was significantly different. Since that is the case, there
should only be one pin used as a tie point, for the filament voltage
dropping resistor.


Because the unused socket elements couple electrostatically with the filiment/cathode,
and make excellent collectors of dust, launchers of corona, and generators
of squeal in the audio. Besides, there isn't all that much extra power
available in the HV circuit, you want to squelch as many leakage paths
as possible.

-Chuck