17JB6A — Beam Power Tube

The 17JB6A is a Novar-type beam power tube designed primarily for use as a high-efficiency horizontal-deflection amplifier in television receivers. It is characterized by its compact envelope design, high peak current capabilities, and specialized ratings for both horizontal and vertical deflection services.

Overview and Physical Construction

The 17JB6A is a beam power pentode featuring a Novar construction. It is designed with a T-12 glass envelope that is shorter than the standard 17JB6 bulb, incorporating an exhaust tip at the bottom. The tube requires a standard Novar 9-contact socket for operation.

Physical Dimensions

Related Designations

The 17JB6A is electrically identical to the 6JB6A and 12JB6A, differing only in its heater ratings. It is also identical to the 17JB6 except for its shorter bulb and the bottom-positioned exhaust tip.

Heater Characteristics and Ratings

The 17JB6A is designed for series or parallel heater chains, featuring a controlled warm-up time to ensure reliable operation in series-string television receivers.

• Heater Voltage (AC or DC): 16.8 V
• Heater Current: 0.450 A (with an allowable tolerance of  0.030 A)
• Average Heater Warm-up Time: 11 seconds

Heater-Cathode Voltage Limits

• Peak Value: 200 max V
• Average Value: 100 max V

Basing and Pinout Configurations

Depending on the manufacturing record and specific application layout, the 9QL basing designation for the 17JB6A is documented with variations in pin assignments. Designers must verify the specific socket wiring configuration:

Pinout Configuration A

• Pin 1: Heater (H)
• Pin 2: Grid No. 1 (G1)
• Pin 3: Cathode (K)
• Pin 4: Grid No. 2 (G2)
• Pin 5: Grid No. 3 (G3)
• Pin 6: Grid No. 1 (G1)
• Pin 7: Plate (P)
• Pin 8: Grid No. 2 (G2)
• Pin 9: Heater (H) / Internal Connection (IC)

Pinout Configuration B

• Pin 1: Grid No. 1 (G1)
• Pin 2: Grid No. 2 (G2)
• Pin 3: Cathode (K)
• Pin 4: Heater (H)
• Pin 5: Heater (H)
• Pin 6: Grid No. 1 (G1)
• Pin 7: Grid No. 2 (G2)
• Pin 8: Grid No. 3 (G3)
• Pin 9: Internal Connection (IC)

Pinout Configuration C

• Pin 1: Grid No. 2 (G2)
• Pin 2: Grid No. 1 (G1)
• Pin 3: Cathode (K)
• Pin 4: Heater (H)
• Pin 5: Heater (H)
• Pin 6: Grid No. 1 (G1)
• Pin 7: Grid No. 2 (G2)
• Pin 8: Grid No. 3 (G3)
• Pin 9: Internal Connection (IC)
• Top Cap: Plate (P)

Electrical Characteristics and Class A1 Operation

The 17JB6A can be operated in either triode or pentode configurations. High-current measurements are performed using a recurrent waveform method to prevent the tube from exceeding its maximum dissipation limits during testing.

Direct Interelectrode Capacitances (Approximate)

• Grid No. 1 to Plate: 0.2 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 pF

Typical Operating Points

Note: Measured using a recurrent waveform method.

Deflection Amplifier Service

The 17JB6A is rated for both horizontal- and vertical-deflection amplifier service in television receivers operating on standard 525-line, 30-frame systems. The design-maximum ratings must not be exceeded under normal operating conditions.

Horizontal-Deflection Amplifier Service

For horizontal-deflection service, the tube is subjected to high peak voltages and currents during the flyback interval.

• DC Plate Supply Voltage: 770 max V
• Peak Positive-Pulse Plate Voltage: 6500 max V (Pulse duration must not exceed 15% of a horizontal scanning cycle, or 10 Ιs)
• Peak Negative-Pulse Plate Voltage: 1500 max V
• DC Grid No. 3 Voltage: 70 max V (A positive bias, typically 30 V, may be applied to minimize "snivets" interference)
• DC Grid No. 2 Voltage: 220 max V
• DC Grid No. 1 Voltage: -55 max V
• Peak Negative-Pulse Grid No. 1 Voltage: 330 max V
• Peak Cathode Current: 550 max mA
• Average Cathode Current: 175 max mA
• Plate Dissipation: 17.5 max W (A bias resistor or other protective means is required to safeguard the tube in the absence of excitation)
• Grid No. 2 Input: 3.5 max W
• Bulb Temperature (at hottest point): 240 max C
• Maximum Grid No. 1 Circuit Resistance (Grid-resistor-bias): 1 max M̦

Vertical-Deflection Amplifier Service

• DC Plate Voltage: 350 max V
• Peak Positive-Pulse Plate Voltage: 2500 max V (Pulse duration must not exceed 15% of a vertical scanning cycle, or 2.5 ms)
• Grid No. 2 Voltage: 300 max V
• Peak Cathode Current: 260 max mA
• Average Cathode Current: 75 max mA
• Plate Dissipation: 15 max W (Protective resistor or other means required in the absence of excitation)
• Grid No. 2 Input: 2.75 max W (Protective resistor or other means required in the absence of excitation)
• Bulb Temperature (at hottest point): 200 max C
• Maximum Grid No. 1 Circuit Resistance (Fixed-bias): 1 max M̦
• Maximum Grid No. 1 Circuit Resistance (Cathode-bias): 2.2 max M̦

Qualitative Curve Observations

When evaluating the plate characteristics of the 17JB6A with Grid No. 3 connected to the cathode and Grid No. 2 held at a constant 150 V, several distinct behaviors are observed:

• Plate Current ($I_b$): At a control grid voltage ($E_{[C1](/tubes/C1)}$) of 0 V, the plate current rises sharply, forming a distinct knee at approximately 40 to 50 plate volts. Beyond this knee, the current flattens out, peaking in the range of 390 mA to just over 400 mA.
• Grid No. 2 Current ($I_{C2}$): At $E_{[C1](/tubes/C1)} = 0\text{ V}$, the screen grid current starts very high (approximately 150 mA) at low plate voltages below 40 V. As the plate voltage increases and passes the knee, the screen current drops rapidly, falling below 50 mA and stabilizing at a much lower value.

Technical Summary

The 17JB6A is a robust, high-performance Novar beam power tube optimized for television deflection circuits. Operating with a 16.8 V, 0.45 A heater, it provides high peak cathode current capabilities (up to 550 mA in horizontal deflection service) and can withstand peak positive plate pulses up to 6500 V. Its compact T-12 envelope with a bottom exhaust tip allows for efficient space utilization in television chassis while maintaining high thermal and electrical reliability.