6-4

6.3Volt Operating Heater, 4-Second Nominal Time Delay, Normally Open (NO) Hermetically Sealed Thermal Time Delay Relay, engineered to interface directly with standard 6.3V vacuum-tube filament heater supply rails. It translates low-voltage AC/DC control energy into a highly repeatable 4-second mechanical close movement, providing absolute physical alignment tracking and baseline stability across vintage audio amplifiers and receiver backplanes, housed in a standard clear glass tube envelope.[1]