U76

The U76 is a half-wave vacuum rectifier for power supplies, also documented in our sources for television use. It is indirectly heated, with separate heater and cathode connections. The U76 sheet gives 30 V and 0.16 A for the heater on AC or DC. These figures concern heating, not the DC current available at the rectified output. The 160 mA figure is also the stated reference for series-heater operation.

The technical sheet lists maximum AC plate voltage 250 V RMS and DC output current 100 mA with a capacitor-input filter. A shared note ties these data to a 100 Ω plate-series resistor. That condition forms part of the specification: 100 mA is not independent of resistance and filter arrangement. Our sources also describe a 40 µF reservoir capacitor in the intended circuit. RMS AC input, DC output and filter capacitance are different quantities requiring the circuit to be read as a whole.

Other listed limits include 700 V peak inverse plate voltage, 500 mA peak plate current and 350 V DC heater-to-cathode potential. Peak current is not the 100 mA DC delivered to the load: capacitor charging takes place during conduction intervals and must be considered with series limiting. Separate heater and cathode do not remove their insulation limit. The available sheet does not specify the polarity of the 350 V figure, so it cannot establish additional limits for each voltage direction.

The base belongs to the International Octal family. In the bottom-view diagram, heater is on 2 and 7, plate on 5 and cathode on 8; pin 1 is explicitly unconnected. The sheet assigns no other connections to 3, 4 and 6. This primary-source reading is more precise than the imported internal-connection claim for pin 1. Document maxima are 3²⁵⁄₃₂ inches overall length and 1⁵⁄₁₆ inches diameter, exactly 96.04375 and 33.3375 mm on conversion. These are maximum dimensions, distinct from measurements of individual specimens. The scanned sheet identifies neither the dimensions' manufacturer nor an edition date.

Documentation consulted: U76 Half-Wave High-Vacuum Rectifier, technical sheet with electrical data, maximum dimensions and pinout; manufacturer and date are absent from the available scan.