14J7 — Triode-Heptode Converter

The 14J7 is an indirectly heated triode-heptode converter vacuum tube designed for frequency conversion service. It integrates a triode oscillator section and a heptode mixer section within a single envelope, sharing a common cathode.

Physical and Heater Specifications

The 14J7 is constructed with an indirectly heated cathode. The heater is designed with the following electrical ratings:

• Heater Voltage: 12.6 V
• Heater Current: 0.15 A
• Cathode Type: Heater (Htr)

Physically, the tube is defined by the 9-30 outline drawing and utilizes an 8BL base connection.

Pinout and Base Configuration

The 14J7 uses an 8-pin base designated as 8BL. The pin connections, viewed from the bottom of the tube, are assigned as follows:

• Pin 1: Heater (H)
• Pin 2: Heptode Plate ($P_H$)
• Pin 3: Grids 2 and 4 ($G_2, G_4$)
• Pin 4: Heptode Grid 3 ($G_3$)
• Pin 5: Triode Grid and Heptode Grid 1 ($G_T, G_1$)
• Pin 6: Triode Plate ($P_T$)
• Pin 7: Cathode and Heptode Grid 5 ($K, G_5$)
• Pin 8: Heater (H)

In this configuration, the triode grid is internally connected to the first grid of the heptode section ($G_1$), which is typical for converter designs where the oscillator signal is injected directly into the mixer.

Maximum Ratings

To ensure safe and reliable operation, the 14J7 must be operated within its maximum design limits:

• Maximum Plate Voltage: 300 V
• Maximum Screen Voltage: 100 V

Converter Operating Points and Characteristics

Under typical operating conditions as a converter, the heptode and triode sections are biased to achieve efficient frequency conversion. The typical operating parameters are:

• Plate Voltage: 250 V
• Screen Voltage: 100 V
• Negative Grid Voltage: 3.0 V
• Plate Current: 1.4 mA
• Screen Current: 2.8 mA
• Plate Resistance ($r_p$): Approximately 1,500,000 Ω (1.5 MΩ)
• Conversion Transconductance ($g_c$): 290 µmhos

Oscillator Section Operating Conditions

The oscillator portion of the converter operates with the following specific parameters:

• Oscillator Grid Current ($I_{g1}$): 0.4 mA
• Oscillator Grid Resistor ($R_{g1}$): 50,000 Ω
• Triode Oscillator Plate Voltage ($E_b$): 250 V (supplied through a 20,000 Ω resistor)
• Triode Plate Current ($I_b$): 5.0 mA

Technical Summary

The 14J7 is a specialized triode-heptode converter tube featuring a 12.6 V, 0.15 A heater and an 8BL base. It is rated for a maximum plate voltage of 300 V and a maximum screen voltage of 100 V. In typical converter service, it provides a conversion transconductance of 290 µmhos with a heptode plate current of 1.4 mA and an oscillator triode plate current of 5.0 mA.