12GJ5A — Beam Power Pentode

The 12GJ5A is a Novar-type beam power pentode designed primarily for use as a high-efficiency horizontal-deflection-amplifier tube in television receivers. It is characterized by its high peak plate current capabilities, robust pulse voltage ratings, and a specialized Novar 9-pin construction. The 12GJ5A is electrically identical to the 6GJ5A and 17GJ5A, differing only in its heater ratings.

Construction, Physical Dimensions, and Basing

The 12GJ5A features a Novar T-12 glass envelope and utilizes a Novar Button 9-pin base (designated as E9-88), which includes an exhaust tip on the base. This construction requires a standard Novar 9-contact socket. The tube also incorporates a top cap connection (compatible with C1-2, C1-3, or C1-33 connectors) for the high-voltage plate terminal, minimizing the risk of arcing.

The physical dimensions of the 12GJ5A are as follows:

• Maximum Diameter: 1.562 inches
• Maximum Seated Height: 3.125 inches
• Maximum Overall Height: 3.505 inches

The 12GJ5A, along with its sister types 6GJ5A and 17GJ5A, is identical to the older 12GJ5, 6GJ5, and 17GJ5 families, except for the base configuration (which features the exhaust tip at the bottom) and a shorter bulb design.

The tube uses the 9QK basing arrangement, which provides the following pin connections (viewed from the bottom of the base):

• Pin 1: Grid No. 3 (Beam Plates)
• Pin 2: Grid No. 1
• Pin 3: Grid No. 2 (Screen Grid)
• Pin 4: Heater
• Pin 5: Heater
• Pin 6: Grid No. 1
• Pin 7: Grid No. 2
• Pin 8: Internal Connection (Do Not Use)
• Pin 9: Internal Connection (Do Not Use)
• Top Cap: Plate

Heater and Cathode Characteristics

The 12GJ5A is designed with an indirectly heated, unipotential cathode. The heater is designed for series-string television receiver applications, featuring a controlled warm-up time to ensure reliable operation when connected in series with other tubes.

For comparison, the 6GJ5A utilizes a 6.3 V, 1.2 A heater, while the 17GJ5A utilizes a 16.8 V, 0.45 A heater. All other electrical and physical characteristics remain identical across these three designations.

Direct Interelectrode Capacitances

The approximate direct interelectrode capacitances of the 12GJ5A, measured without an external shield, are:

• Grid No. 1 to Plate: 0.26 pF
• Grid No. 1 to Cathode, Heater, Grid No. 2, and Grid No. 3: 15 pF
• Plate to Cathode, Heater, Grid No. 2, and Grid No. 3: 6.5 pF

Class A1 Amplifier Characteristics

The 12GJ5A can be operated as a Class A1 amplifier in either a triode-connected or pentode-connected configuration. The typical operating characteristics under these conditions are detailed below:

Triode Connection

In this configuration, Grid No. 2 is connected to the plate:

• Plate Voltage: 150 V
• Grid-No. 2 Voltage: 150 V
• Grid-No. 1 Voltage: -22.5 V
• Amplification Factor (Mu-Factor, Grid No. 2 to Grid No. 1): 4.4

Pentode Connection

Under pentode operation, the tube exhibits the following characteristics at two distinct operating points:

Horizontal-Deflection Amplifier Service and Ratings

The primary application of the 12GJ5A is within the horizontal-deflection-amplifier stage of television receivers operating under a standard 525-line, 30-frame scanning system. Due to the demanding nature of this service, which involves high-voltage flyback pulses and significant current swings, the tube is rated under the Design-Maximum System with strict limits.

Maximum Ratings (Design-Maximum Values)

• DC Plate Supply Voltage: 770 V
• Peak Positive-Pulse Plate Voltage: 6,500 V (The pulse duration must not exceed 15% of a horizontal scanning cycle, equivalent to 10 microseconds)
• Peak Negative-Pulse Plate Voltage: 1,500 V
• DC Grid-No. 2 (Screen Grid) Voltage: 220 V
• DC Grid-No. 1 (Control Grid) Voltage: -55 V
• Peak Negative-Pulse Grid-No. 1 Voltage: 330 V
• Peak Cathode Current: 550 mA
• Average Cathode Current: 175 mA
• Plate Dissipation: 17.5 W
• Grid-No. 2 Input: 3.5 W
• Maximum Bulb Temperature (at hottest point): 248 °C

Maximum Circuit Values

• Grid-No. 1-Circuit Resistance (for grid-resistor-bias operation): 1.0 megohm

To protect the tube from excessive dissipation in the event of a loss of excitation, a cathode bias resistor or other protective means must be employed in the circuit.

Average Characteristics and Related Designations

For the average characteristic curves of the 12GJ5A, reference is made to the curves of the 6GW6 beam power tube, which shares similar plate and grid characteristics.

The 12GJ5A is part of a family of identical tubes that includes the 6GJ5A and 17GJ5A. These three types differ solely in their heater configurations to accommodate different power supply designs (such as parallel 6.3 V transformer supplies or series-string heater circuits). They represent an updated design over the original 12GJ5, 6GJ5, and 17GJ5 types, featuring a more compact bulb and a modified Novar base with the exhaust tip located on the bottom.

Technical Summary

The 12GJ5A is a high-performance Novar beam power pentode designed for horizontal-deflection-amplifier service in television receivers. Operating with a 12.6 V, 0.6 A heater with an average 11-second warm-up time, it is optimized for series-string heater circuits. The tube features a Novar T-12 envelope, a 9-pin E9-88 base with an exhaust tip, and a top cap plate connection.

In horizontal-deflection service, it supports a peak positive-pulse plate voltage of 6,500 V and a peak cathode current of 550 mA, with a maximum plate dissipation of 17.5 W. Under typical Class A1 pentode conditions, it provides a transconductance of 7,100 µmhos and a plate resistance of approximately 15,000 Ω. The 12GJ5A offers a compact, high-efficiency solution for television deflection circuits, combining robust pulse capabilities with reliable series-string heater performance.