The flanged-header grid terminal is a design feature of particular value when the 9C25 is used in grounded-grid circuits. In such circuits, this terminal when used with a large circular connector effectively isolates the filamenmt from the plate circuit, and provides a direct, low-inductance path to the grid. As a result, neutralization is generally unnecessary in grounded-grid service. In grounded-filament circuits, the 9C25 can be used in the conventional manner.
The design of the 9C25 also includes an effective external radiator for cooling the plate by forced air; a single-phase, multistrand, thoriated tungsten filament; and a strong, conical grid support which provides a maximum of shielding between plate and filament to give extremely low plate-filament capacitance, and also serves to reduce effectively the grid-lead inductance.