New-Old-Stock (NOS) tube. The 5U4GB is a filamentary twin diode designed for use as a full-wave rectifier in the power supply of television receivers or other equipment which has high direct-current requirements. The 5U4GB may be used a replacement for either the 5U4G or the 5U4GA. Note: brands may vary. Photo is for reference only and may not exactly represent final product received.