17DQ6B — Beam Power Pentode

An indirectly heated beam power tube designed for horizontal-deflection amplifier service in television receivers, featuring high efficiency and controlled heater warm-up characteristics.

Overview

The 17DQ6B (also designated as 17DQ6-B or within the 17GW6/17DQ6B family) is a glass octal beam power pentode. It is primarily designed for use as a horizontal-deflection output amplifier in high-efficiency deflection circuits of television receivers. Due to its ability to deliver high zero-bias plate current at low plate and screen-grid voltages, the tube is exceptionally well-suited for receivers operating with low plate-supply voltages.

In terms of electrical characteristics, the 17DQ6B is identical to the 6DQ6B (or 6GW6/6DQ6B) and the 12DQ6B (or 12GW6/12DQ6B) except for its heater voltage, current, and warm-up ratings. It is also identical to the 17GW6, with which it is frequently co-designated.

Construction, Physical Dimensions, and Pinout

The 17DQ6B is constructed in a T-12 glass envelope (JEDEC outline 12-19 or 12-51) with a coated unipotential cathode. The tube can be mounted in any position. It features a skirted miniature top cap (JEDEC C1-2 or C1-3) for the plate connection, which isolates the high-voltage pulse present on the anode during horizontal retrace.

Physical Dimensions

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

Base and Pinout Configuration

The tube utilizes an octal base, which can be a 5, 6, or 7-pin configuration (such as JEDEC B5-190, B6-122, B6-148, B7-111, or B7-119). When using the 6-pin bases (B6-122 or B6-148), Pin 1 is omitted. The electrical connections follow the JEDEC 6AM basing diagram:

Direct Interelectrode Capacitances

The approximate capacitances of the tube, measured without an external shield, are:

• Grid No. 1 to Plate (G1 to P): 0.5 pF
• Input (G1 to H + K + G3 + G2): 15.0 pF (up to 17.0 pF depending on the specific grounding configuration)
• Output (P to H + K + G3 + G2): 7.0 pF

Heater Ratings and Series-String Operation

The 17DQ6B is designed for use in television receivers employing series-connected heater strings. It incorporates a controlled heater warm-up characteristic to ensure dependable operation and minimize voltage surges across other tubes in the string during start-up.

• Heater Voltage (AC or DC): 16.8 V
• Heater Current: 0.45 A (450 mA) with a tolerance of ±6% (450 ± 30 mA)
• Heater Warm-up Time: 11 seconds. This is defined as the time required for the heater voltage to reach 80% of its rated value when four times the rated voltage (67.2 V) is applied to the heater in series with an external resistance equal to three times the rated heater voltage divided by the rated current (112 ohms).

Heater-Cathode Voltage Limits

To prevent insulation breakdown between the heater and the cathode, the following design-maximum voltage limits must be observed:

• Heater Negative with Respect to Cathode: 200 V max. (Total DC and Peak)
• Heater Positive with Respect to Cathode:
  • DC Component: 100 V max.
  • Total DC and Peak: 200 V max.

Electrical Characteristics and Typical Operating Points

The 17DQ6B can be operated in either pentode or triode configurations. Because of its application in both monochrome and color television receivers, manufacturers established two distinct sets of typical operating characteristics.

Pentode Connection Characteristics

At higher plate voltages, such as Eb = 5000 V with Ec2 = 150 V, the control grid cutoff voltage shifts significantly to approximately -100 V.

Triode Connection Characteristics

When Grid No. 2 is connected directly to the plate, the tube exhibits the following typical characteristics:

• Under Standard Conditions (Eb = Ec2 = 150 V, Ec1 = -22.5 V):
  • Amplification Factor (mu): 4.4
• Under High-Rating Conditions (Eb = Ec2 = 125 V, Ec1 = -25 V):
  • Amplification Factor (mu): 3.3

Instantaneous Plate Knee Values

The tube is capable of delivering high peak currents at low plate voltages, which is a critical requirement for horizontal deflection service. These values are measured using a recurrent waveform method or during short intervals (maximum of 2 seconds) to prevent exceeding the maximum dissipation ratings:

• Standard Conditions (Eb = 60 V, Ec2 = 150 V, Ec1 = 0 V):
  • Plate Current (Ib): 345 mA (up to 390 mA)
  • Grid No. 2 Current (Ic2): 27 mA (up to 32 mA)
• High-Rating Conditions (Eb = 70 V, Ec2 = 125 V, Ec1 = 0 V):
  • Plate Current (Ib): 550 mA
  • Grid No. 2 Current (Ic2): 42 mA

Horizontal-Deflection Amplifier Ratings

The 17DQ6B is rated under the Design-Maximum Rating System (EIA Standard RS-239). The maximum ratings differ depending on whether the tube is employed in standard monochrome television service or high-rating color television service. Both rating sets are specified for a standard 525-line, 30-frame system, where the peak positive pulse duration must not exceed 15% of one horizontal scanning cycle (or a maximum of 10 us).

Circuit Protection Requirements

In stages operating with grid-leak bias, an adequate cathode bias resistor or other protective means must be incorporated into the circuit. This protection is necessary to prevent excessive plate and screen dissipation and safeguard the tube from damage in the event that the horizontal excitation signal is lost.

Qualitative Curve Observations

The average plate and transfer characteristics of the 17DQ6B reveal several key design features:

• Plate Characteristics at Zero Bias (Ec1 = 0 V): When plate current (Ib) and screen-grid current (Ic2) are plotted against plate voltage (Eb) for various screen voltages (Ec2) from 50 V to 200 V, the plate current rises extremely steeply at very low plate voltages. It exhibits a sharp knee below 50 V to 100 V, above which the current levels off and remains highly flat and constant across the 100 V to 500 V range. This flat saturation region indicates high plate resistance and stable operation.
• Screen Grid Current Behavior: At zero control-grid bias (Ec1 = 0 V), the screen-grid current (Ic2) peaks sharply at low plate voltages (below 50 V), where the plate is less effective at attracting electrons. As the plate voltage increases past the knee, the screen-grid current drops rapidly and stabilizes at a very low, safe operating level.
• Transfer Characteristics: Plots of plate and screen currents versus control-grid voltage (Ec1) from -60 V to 0 V show a smooth, predictable cutoff behavior. The knee of the plate current curves occurs at progressively lower plate voltages as the control-grid bias becomes more negative.

Technical Summary

The 17DQ6B is a high-performance, octal-based beam power pentode optimized for horizontal-deflection amplifier service in television receivers. Operating with a 16.8 V, 0.45 A heater with an 11-second controlled warm-up time, it is designed for integration into series heater strings.

The tube is characterized by its ability to deliver high peak plate currents (up to 1,000 mA under color TV pulse conditions) at low plate voltages, a well-defined plate knee, and robust design-maximum ratings. Depending on the application, it can support plate dissipations up to 24 W and peak positive pulse voltages up to 7,000 V. These characteristics make the 17DQ6B a highly efficient and reliable choice for both monochrome and color television deflection circuits.