The term **40C5** typically refers to a specific type of **vacuum tube** (thermionic valve) that was widely used in mid-20th-century consumer electronics, particularly in radio and television audio output stages. --- ### 1. Technical Overview The 40C5 is a **Beam Power Pentode**. It was designed specifically for use as an audio power amplifier in equipment where the heater (filament) string is connected in series, a common design in "transformerless" AC/DC tabletop radios. ### 2. Key Specifications Below are the typical electrical characteristics for the 40C5 vacuum tube: | Characteristic | Specification | | :--- | :--- | | **Tube Type** | Beam Power Pentode | | **Base Type** | Miniature 7-Pin (7BD) | | **Heater Voltage** | 40 Volts | | **Heater Current** | 150 mA (0.15 A) | | **Max Plate Voltage** | 150 V | | **Max Screen Voltage** | 130 V | | **Power Output** | Approx. 1.9 Watts | --- ### 3. Pin Configuration The 40C5 uses a standard 7-pin layout. Looking at the bottom of the tube (clockwise from the gap): 1. **Pin 1:** Control Grid ($G_1$) 2. **Pin 2:** Cathode & Beam Plates 3. **Pin 3:** Heater 4. **Pin 4:** Heater 5. **Pin 5:** Control Grid ($G_1$) - *Internal Connection* 6. **Pin 6:** Screen Grid ($G_2$) 7. **Pin 7:** Plate (Anode) --- ### 4. Typical Applications * **Tabletop Radios:** Used as the final audio output stage to drive the speaker. * **Series-String Circuits:** Because it requires **40 Volts** for the heater, it was often wired in series with other tubes (like the 12BE6, 12BA6, etc.) so that the total voltage drop equaled the mains voltage (110-120V), eliminating the need for a heavy power transformer. * **Phonographs:** Found in small portable record players of the 1950s and 60s. ### 5. Equivalent and Similar Tubes If you are looking for replacements or similar parts: * **50C5:** Nearly identical but requires 50V for the heater. It is much more common than the 40C5. * **35C5:** A 35V heater version of the same internal architecture. * **17C5:** A 17V heater version. --- **Safety Note:** Devices using the 40C5 are often "Hot Chassis" designs. This means one side of the power cord may be connected directly to the metal frame of the device. Use an isolation transformer when servicing these circuits to avoid electric shock.