17GW6 — Beam Power Pentode

Overview

The 17GW6 (often co-designated as the 17DQ6B) is a glass-envelope beam power pentode designed primarily for service as a horizontal-deflection amplifier in high-efficiency deflection circuits of television receivers, including color television systems. It is characterized by its high zero-bias plate current, high plate-to-screen current ratio, and robust high-voltage ratings. The 17GW6 is electrically identical to the 6GW6 (or 6DQ6B) and 12GW6 (or 12DQ6B) except for its heater ratings.

Construction, Mechanical Specifications, and Pinout

The 17GW6 is typically constructed with a T-12 glass bulb and a short medium shell octal base (such as the JEDEC B5-190, B6-122, B6-148, B7-111, or B7-119 configurations) featuring external barriers. Some variants utilize a Novar base and envelope construction. The physical dimensions of the octal variant include a maximum diameter of 1.562 to 1.563 inches, a maximum seated height of 3.688 inches, and a maximum overall height of 4.250 inches (JEDEC outline 12-19). The tube features a skirted miniature top cap (C1-2 or C1-3) for the plate connection, which isolates the high-voltage anode pulses from the base pins. The tube can be mounted in any position.

The JEDEC 6AM basing diagram defines the pin connections as viewed from the bottom:

• Pin 1: No Connection (NC)
• Pin 2: Heater
• Pin 3: No Connection (NC) or Metal Collar / Internal Connection (MC) (omitted when the B5-190 base is used)
• Pin 4: Grid No. 2 (Screen Grid)
• Pin 5: Grid No. 1 (Control Grid)
• Pin 7: Heater
• Pin 8: Cathode and Grid No. 3 (Suppressor Grid)
• Top Cap: Plate

Heater Ratings

The 17GW6 features a coated unipotential cathode. The heater is designed for series-connected heater strings and has a controlled warm-up characteristic to ensure reliable operation in television receivers.

• Heater Voltage (AC or DC): 16.8 V
• Heater Current: 0.45 A (450 mA) ± 6% (or a supply limit of 450 ± 30 mA)
• Average Heater Warm-up Time: 11 seconds
• Calculated Heater Power: 16.8 V × 0.45 A = 7.56 W

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

• Heater negative with respect to cathode: 200 V maximum (Total DC and Peak)
• Heater positive with respect to cathode: 200 V maximum (Total DC and Peak), with the DC component restricted to a maximum of 100 V.

Electrical Characteristics and Operating Points

The electrical characteristics of the 17GW6 are documented under several distinct operating conditions, including typical Class A1 pentode operation, low-voltage zero-bias pentode operation, and triode-connected operation.

Typical Pentode Operation (Class A1)

• Plate Voltage: 250 V
• Grid No. 2 Voltage: 150 V
• Grid No. 1 Voltage: -22.5 V
• Plate Current: 65 mA to 70 mA
• Grid No. 2 Current: 1.8 mA to 2.1 mA
• Plate Resistance (Approximate): 15,000 to 18,000 ohms
• Transconductance: 7,100 to 7,300 µmhos
• Grid No. 1 Cutoff Voltage (for plate current of 1 mA): -42 V (approximate)

Low-Voltage Pentode Operation (Zero Bias)

To evaluate the tube's performance at the "knee" of its characteristic curve without exceeding maximum dissipation ratings, measurements are taken using a recurrent waveform method (or short intervals of maximum 2 seconds):

• Plate Voltage: 60 V
• Grid No. 2 Voltage: 150 V
• Grid No. 1 Voltage: 0 V
• Plate Current: 345 mA to 390 mA
• Grid No. 2 Current: 27 mA to 32 mA

Triode-Connected Operation

When Grid No. 2 is connected directly to the plate:

• Plate Voltage: 150 V
• Grid No. 2 Voltage: 150 V
• Grid No. 1 Voltage: -22.5 V
• Amplification Factor (Mu-Factor, G2 to G1): 4.4

Horizontal-Deflection Service and Maximum Ratings

In horizontal-deflection-amplifier service (such as in a 525-line, 30-frame television scanning system), the 17GW6 is subjected to severe pulse voltages. The maximum ratings are established under the Design-Maximum system:

• DC Plate Supply Voltage (Boost + DC Power Supply): 770 V maximum
• Peak Positive-Pulse Plate Voltage: 6500 V maximum (with a pulse duration not exceeding 15% of one horizontal scanning cycle, or a maximum of 10 µs)
• Peak Negative-Pulse Plate Voltage: 1500 V maximum
• DC Grid No. 2 Voltage: 220 V maximum
• DC Grid No. 1 Voltage: -55 V maximum
• Peak Negative-Pulse Grid No. 1 Voltage: 330 V maximum
• Peak Cathode Current: 550 mA to 610 mA maximum
• Average Cathode Current: 175 mA maximum
• Plate Dissipation: 17.5 W to 18 W maximum (stages operating with grid-resistor bias require a cathode-bias resistor or other protective means to safeguard the tube in the absence of drive/excitation)
• Grid No. 2 Input: 3.5 W to 3.6 W maximum
• Bulb Temperature (at hottest point): 220 °C to 240 °C maximum
• Maximum Grid No. 1 Circuit Resistance: 1.0 MΩ (for grid-resistor-bias operation)

Interelectrode Capacitances

The direct interelectrode capacitances of the 17GW6 are measured without an external shield:

• Grid No. 1 to Plate: 0.5 pF
• 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

Analysis of Characteristic Curves

The average plate characteristics of the 17GW6 demonstrate its high-efficiency design. When plotting plate current and Grid No. 2 current against plate voltage (from 0 to 400 V) under rated heater voltage and a 10% duty cycle, several key behaviors emerge:

• Sharp Knee: The plate current curves exhibit a very sharp knee at low plate voltages, typically around 50 V. Below this knee, the plate current rises rapidly. Above the knee, the plate current flattens out, showing high plate resistance.
• Zero-Bias Performance: At a Grid No. 1 voltage of 0 V and a Grid No. 2 voltage of 150 V, the plate current reaches a peak of nearly 390 to 400 mA. If the Grid No. 2 voltage is increased to 200 V, the peak plate current can exceed 500 mA.
• Grid No. 2 Current Behavior: The Grid No. 2 (screen) current is highly dependent on plate voltage. It peaks sharply at very low plate voltages (below 50 V), reaching approximately 100 mA to 150 mA when the plate voltage is near 0 V and Grid No. 1 is at 0 V. As the plate voltage increases past the knee, the screen current drops rapidly to a low, stable level (typically around 27 mA to 32 mA), minimizing screen grid dissipation during normal conduction cycles.

Technical Summary

The 17GW6 is a high-performance, octal-base beam power pentode designed specifically for horizontal-deflection-amplifier service in television receivers. Featuring a 16.8 V, 0.45 A heater with a controlled 11-second warm-up time, it is optimized for series-string power supplies. With its ability to handle peak positive plate pulses up to 6500 V, peak cathode currents up to 610 mA, and a plate dissipation of up to 18 W, the 17GW6 provides the high peak currents and high-voltage insulation required for driving magnetic deflection yokes. Its electrical characteristics are identical to the 6GW6 and 12GW6 families, offering a robust solution for television sweep circuits.