17JT6A — Novar Beam Power Pentode

The 17JT6A is a Novar beam power tube designed primarily for use as a horizontal-deflection amplifier in high-efficiency deflection circuits of black-and-white television receivers employing wide-angle or high-voltage picture tubes. It belongs to a family of tubes that includes the 6JT6A and 12JT6A, sharing identical electrical characteristics and physical structures except for their heater ratings. Additionally, the 17JT6A is identical to the 6JT6, 12JT6, and 17JT6 types, except that it features a shorter bulb and a base with an exhaust tip on the bottom.

Mechanical Specifications, Base, and Pinout

The 17JT6A is constructed in a T-12 glass envelope with a button 9-pin E9-88 base, requiring a standard Novar 9-contact socket. The physical dimensions of the tube are:

• Maximum Diameter: 1.563 inches
• Maximum Seated Height: 2.500 inches
• Maximum Overall Height: 2.880 inches

The tube utilizes the 9QU basing diagram, which provides the following pin connections:

• Pin 1: Grid No. 2 (Screen Grid)
• Pin 2: Grid No. 1 (Control Grid)
• Pin 3: Cathode, Grid No. 3 (Suppressor Grid / Beam Plates)
• Pin 4: Heater
• Pin 5: Heater
• Pin 6: Grid No. 3
• Pin 7: Grid No. 2
• Pin 8: Internal Connection (IC) — Do Not Use
• Pin 9: Plate

Heater Ratings and Interelectrode Capacitances

The heater of the 17JT6A is designed for series or parallel operation with the following specifications:

• Heater Voltage (AC or DC): 16.8 V
• Heater Current: 0.450 ± 0.030 A
• Average Warm-up Time: 11 seconds

Heater-Cathode Voltage Limits

• Heater Negative with Respect to Cathode: 200 V maximum (Total DC and Peak)
• Heater Positive with Respect to Cathode: 100 V maximum (DC), 200 V maximum (Total DC and Peak)

Direct Interelectrode Capacitances

Measured without an external shield, the direct interelectrode capacitances are:

• Grid No. 1 to Plate: 0.26 pF
• Input (G1 to K, G3, G2, H): 15.0 pF
• Output (P to K, G3, G2, H): 6.5 pF

Electrical Characteristics and Class A1 Operation

The 17JT6A can be operated in either pentode or triode configurations. Under Class A1 conditions, with Grid No. 3 connected to the cathode at the socket, the typical characteristics are:

* Grid No. 2 connected to plate. ** Measured using a recurrent waveform method to avoid exceeding maximum ratings.

Horizontal-Deflection Amplifier Service

For operation in a 525-line, 30-frame television system where the pulse duration does not exceed 15% of one horizontal scanning cycle (approximately 10 microseconds), the design-maximum ratings are:

• DC Plate Supply Voltage: 770 V
• Peak Positive-Pulse Plate Voltage: 6,500 V
• Peak Negative-Pulse Plate Voltage: 1,500 V
• DC Grid No. 3 Voltage: 70 V (A positive voltage up to 30 V may be applied to reduce "snivets" interference)
• DC Grid No. 2 Voltage: 220 V
• DC Grid No. 1 Voltage (Negative-bias): 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 (Hottest Point): 240 °C
• Maximum Grid No. 1 Circuit Resistance (Grid-Resistor-Bias): 1.0 MΩ

Note: In stages operating with grid-leak bias, an adequate cathode bias resistor or other protective means is required to safeguard the tube in the absence of excitation.

Qualitative Curve Observations

The plate characteristics (Ib vs. Eb) with Grid No. 3 connected to the cathode and Grid No. 2 held at 150 V reveal a highly defined knee. At a Grid No. 1 voltage of 0 V, the plate current rises very steeply to a sharp knee between 50 V and 75 V (specifically around 50 V to 60 V), where it reaches approximately 390 mA. Beyond this knee, the plate current remains nearly flat as the plate voltage increases up to 300 V.

Conversely, the Grid No. 2 current (Ic2) at a Grid No. 1 voltage of 0 V starts extremely high (approximately 150 mA) at zero plate voltage and drops rapidly to a low baseline level of about 20 to 30 mA once the plate voltage rises past the knee.

Technical Summary

The 17JT6A is a robust Novar beam power pentode optimized for high-efficiency horizontal-deflection amplifier service. Operating with a 16.8 V heater, it delivers high peak plate currents (up to 390 mA at the knee) and can withstand peak positive plate pulses up to 6,500 V. Its physical design features a compact T-12 envelope with a bottom exhaust tip, making it a reliable and space-efficient choice for television receiver circuits.