An electron gun comprises an electron emitter, an electrode surrounding the electron emitter, an extraction electrode, and a double condenser lens assembly, the double condenser lens assembly comprising a magnetic immersion pre-condenser lens and a condenser lens. Tunable ferro-electric capacitors are used to tune the resonant frequencies of several resonators used in a multiplexer and to tune the frequency response shape of the multiplexer. The CPRU provides the voice access unit over-the-air, i. In another embodiment, the groups of display elements are configured to have different actuation voltages and are driven by pulses of varying voltage indicative of those actuation voltages.