14F8 High-Frequency Twin Triode

Overview

The 14F8 is a high-frequency twin triode vacuum tube designed for amplification and signal processing applications. It features two independent triode sections housed within a single envelope, utilizing an indirectly heated cathode design. The tube is characterized by a 12.6 V heater rating and is optimized for Class A amplifier service, where it provides a relatively high amplification factor of 48.

Mechanical Specifications and Base Connections

The 14F8 is constructed with an indirectly heated cathode. It utilizes the 8BW base connection configuration and is defined by the 9-32 outline drawing.

The heater is designed to operate under the following electrical specifications:

• Heater Voltage: 12.6 V
• Heater Current: 0.15 A
• Calculated Heater Power: 1.89 W (calculated as 12.6 V multiplied by 0.15 A)

Electrical Ratings and Class A Operating Points

The maximum rated plate voltage for the 14F8 is 300 V.

For Class A amplifier service, the typical operating characteristics are specified per individual triode section. At the documented operating point, the parameters are as follows:

• Plate Voltage: 250 V
• Cathode Bias Resistor: 500 Ω
• Plate Current: 6.0 mA
• Transconductance: 3,300 µmhos (micromhos)
• Amplification Factor: 48

Using these typical operating values, several key parameters can be mathematically derived:

• Calculated Grid Bias Voltage: Under the specified operating conditions, the plate current of 6.0 mA flowing through the 500 Ω cathode resistor produces a calculated negative grid bias voltage of 3.0 V (calculated as 0.006 A multiplied by 500 Ω).
• Calculated Plate Resistance: Although the plate resistance is not directly tabulated, applying the fundamental triode relationship (plate resistance equals amplification factor divided by transconductance) yields a calculated plate resistance of approximately 14,545 Ω (calculated as 48 divided by 0.0033 S).

Interelectrode Capacitances

The interelectrode capacitances of the 14F8 are specified without an external shield. The capacitance values for the internal structure are:

• Input Capacitance: 2.8 pF (micromicrofarads)
• Output Capacitance: 1.4 pF (micromicrofarads)
• Grid-to-Plate Capacitance: 1.6 pF (micromicrofarads)

Technical Summary

The 14F8 is a high-frequency twin triode featuring a 12.6 V, 0.15 A heater, an 8BW base, and a maximum plate voltage rating of 300 V. Operating as a Class A amplifier, each section typically runs at a plate voltage of 250 V with a 500 Ω cathode bias resistor, drawing 6.0 mA of plate current. At this operating point, it exhibits a transconductance of 3,300 µmhos and an amplification factor of 48, making it a versatile choice for high-frequency voltage amplification.