12GW6 — Beam Power Pentode

An octal-based beam power pentode designed for service as a horizontal-deflection output amplifier in television receivers, featuring high efficiency, controlled heater warm-up, and high peak current capabilities.

Overview

The 12GW6 is a glass-octal beam power pentode engineered primarily for use as a horizontal-deflection amplifier in high-efficiency deflection circuits of television receivers. It is designed to operate effectively in circuits with low plate supply voltages and is characterized by high zero-bias plate current, a high ratio of plate current to screen-grid (grid No. 2) current, and high DC plate supply voltage ratings.

The 12GW6 is electrically identical to the 6GW6 (or 6GW6/6DQ6B) and the 17GW6 (or 17GW6/17DQ6B) except for its heater ratings. It is frequently co-designated as the 12GW6/12DQ6B or 12DQ6B/12GW6, representing its dual-standard nomenclature.

Heater Characteristics and Series-String Operation

The 12GW6 features an indirectly heated, coated unipotential cathode. It is specifically designed for use in television receivers employing series-connected heater strings, where the picture-tube heater and other tube heaters are wired in series. To minimize heater voltage surges across individual tubes during startup, the 12GW6 incorporates a controlled heater warm-up characteristic.

The heater warm-up time is defined as the time required for the voltage across the heater to reach 80% of its rated value after applying four times the rated heater voltage to a circuit consisting of the tube heater in series with an external resistance equal to three times the nominal heater operating resistance.

Heater-to-cathode voltage limits are strictly defined to prevent insulation breakdown:

• Heater Negative with Respect to Cathode: The maximum allowable total DC and peak voltage is 200 V.
• Heater Positive with Respect to Cathode: The maximum allowable total DC and peak voltage is 200 V, with the DC component restricted to a maximum of 100 V.

Mechanical Design, Basing, and Pinout

The 12GW6 is constructed in a T-12 glass envelope with a short medium shell octal base. Depending on the manufacturer and specific base style (such as JEDEC B6-122, B5-190, B6-148, B7-111, or B7-119), the base may feature 5, 6, or 7 pins. When the B5-190 base style is utilized, pin number 3 is omitted. The tube features a skirted miniature top cap (JEDEC C1-2 or C1-3) for the high-voltage plate connection, which isolates the high-pulse plate voltage from the other base pins.

The tube utilizes the JEDEC 6AM basing diagram. The pin connections, viewed from the bottom of the base, are as follows:

The physical dimensions of the envelope are:

• Maximum Diameter: 1.563 inches
• Maximum Seated Height: 3.688 inches
• Maximum Overall Height: 4.250 inches

The 12GW6 can be mounted and operated in any position.

Direct Interelectrode Capacitances

The direct interelectrode capacitances of the 12GW6 are measured without an external shield. The typical values are:

• Grid No. 1 to Plate: 0.5 pF (up to 0.6 pF in some specifications)
• Input (Grid No. 1 to Cathode, Heater, Grid No. 2, and Grid No. 3): 15.0 pF to 17 pF
• Output (Plate to Cathode, Heater, Grid No. 2, and Grid No. 3): 7.0 pF

Electrical Characteristics and Operating Points

The 12GW6 can be evaluated under Class A1 amplifier conditions. The published technical literature documents two distinct sets of typical operating characteristics, reflecting different application requirements (such as standard deflection versus high-performance or color television deflection service).

Standard Operating Point

Under standard operating conditions, the tube exhibits the following characteristics:

High-Performance Operating Point

For higher-power deflection applications, Sylvania documents an alternative operating point with significantly higher transconductance and current capability:

• Plate Voltage: 175 V
• Grid No. 2 Voltage: 125 V
• Grid No. 1 Voltage: -25 V
• Plate Current: 110 mA
• Grid No. 2 Current: 5 mA
• Transconductance: 10,500 µmhos
• Plate Resistance (Approx.): 5500 Ω
• Amplification Factor (Triode-connected): 3.3
• Grid No. 1 Cutoff Voltage (for plate current of 1 mA): -75 V

Zero-Bias and Knee Characteristics

The 12GW6 is designed to achieve high plate current at the "knee" of its characteristic curve when the control grid is at zero bias. This is critical for sweeping the electron beam across the television screen efficiently.

• At Eb = 60 V, Ec2 = 150 V, Ec1 = 0 V: The instantaneous plate current reaches 345 mA to 390 mA, while the grid No. 2 current is 27 mA to 32 mA.
• At Eb = 70 V, Ec2 = 125 V, Ec1 = 0 V: The instantaneous plate current reaches 550 mA, while the grid No. 2 current is 42 mA.

Note on Measurement: Because operating the tube at zero bias with continuous DC voltages would quickly exceed the maximum plate and screen-grid dissipation ratings, these knee values must be measured using a recurrent waveform method (or restricted to a short interval of no more than 2 seconds) to prevent permanent damage to the tube.

Horizontal-Deflection Amplifier Ratings and Circuit Requirements

The maximum ratings of the 12GW6 are specified under the Design-Maximum Rating System. Depending on the target application (such as standard black-and-white receivers versus high-demand color television receivers), two distinct sets of maximum ratings are documented.

Pulse Rating Conditions

The peak pulse ratings (such as the 6500 V or 7000 V peak positive plate voltage) are specialized limits intended for horizontal deflection service in a standard 525-line, 30-frame television system. The duty cycle of these pulses must not exceed 15% of one horizontal scanning cycle (which corresponds to a maximum pulse duration of 10 microseconds).

Circuit Protection

When the 12GW6 is operated in stages utilizing grid-resistor bias (or grid-leak bias), the circuit must incorporate an adequate cathode-bias resistor or other protective means. This precaution is mandatory to protect the tube from excessive current and thermal runaway in the event that the horizontal excitation signal is lost.

Technical Summary

The 12GW6 is a robust, glass-octal beam power pentode designed specifically for horizontal-deflection amplifier service in television receivers. Featuring a 12.6 V, 0.6 A heater with a controlled 11-second warm-up time, it is optimized for series-connected heater strings. The tube's design provides high peak cathode currents (up to 1000 mA under pulsed conditions) and high plate dissipation capabilities (up to 24 W in high-performance applications), making it highly efficient in driving deflection coils. With its isolated top-cap plate connection and standard JEDEC 6AM basing, the 12GW6 remains a classic example of specialized television sweep-tube engineering.