The RK-25 is a power pentode designed for use as a final amplifier, oscillator or frequency multiplier. The data-sheet shows values for different types of modulation.
The RK-45 is an HF device with an upper frequency of 30 MHz.
The RK-25 has a ceramic (Isolantite) base and a 6.3 Volt heater. The RK-25B has a Bakelite base. The RK-23 has a 2.5 V heater.
The label declares this to be a 4 pillar tube, referencing the strong internal construction. Strong construction and a ceramic base suggest that it was suitable for aircraft use.
The ceramic supports, the four pillars and the anode with screens within.
The screens match the outer dimension of the suppressor grid. G3 itself is close wound as is required for use as a controlling grid.
The classic envelope is 51 mm in diameter and, excluding the UX7base pins, is 129 mm tall.
