17JM6 — Beam-Power Pentode

The 17JM6 is a high-performance, Compactron-style beam-power pentode designed primarily for use as a horizontal-deflection output amplifier in television receivers. It features high zero-bias plate current, a high ratio of plate current to screen grid (Grid 2) current, and robust voltage ratings capable of handling the high-voltage pulses characteristic of horizontal deflection circuits.

Overview

The 17JM6 is constructed in a T-12 glass envelope using a 12-pin Compactron design. It is engineered to deliver the high peak currents required by horizontal deflection systems in television receivers, particularly color television sets. A key design feature is the separate external connection provided for the beam plates (Grid 3), which allows for independent biasing or connection to suppress "snivets" (high-frequency oscillations that cause vertical lines on television screens).

The tube is electrically identical to the 6JM6 except for its heater characteristics and ratings. It is designed to operate in any mounting position.

Construction, Heater, and Physical Characteristics

The 17JM6 utilizes a coated unipotential cathode and a Compactron T-12 glass envelope. The physical dimensions of the device are standardized as follows:

• Maximum Diameter: 1.563 inches
• Maximum Overall Height: 3.625 inches
• Seated Height: 3.000 to 3.250 inches
• Top Cap: JEDEC C1-3 skirted miniature cap (used for the high-voltage plate connection)
• Base: 12-pin JEDEC E12-74 button base

Heater Ratings

The heater of the 17JM6 is designed for series-string television receiver applications and features a controlled warm-up characteristic.

The heater warm-up time 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 in series with an external resistance equal to three times the rated hot heater resistance.

Heater-Cathode Voltage Limits

To ensure insulation integrity, the maximum voltage differences between the heater and cathode are restricted under the Design-Maximum System:

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

Basing and Pinout Configurations

The 17JM6 has been documented with two primary JEDEC basing configurations: 12FK and 12FJ. Within these designations, minor variations in internal connections and pin assignments exist across different versions.

Basing Diagram 12FK Variations

Under the 12FK basing system, two distinct pinout configurations are recorded:

Basing Diagram 12FJ Variations

Similarly, the 12FJ basing system exhibits two documented configurations:

Due to these variations, circuit designers and technicians must verify the specific basing layout of the physical tube in use to avoid short circuits or improper electrode biasing.

Electrical Characteristics and Typical Operation

The 17JM6 family includes the standard 17JM6 and the revised 17JM6A. While sharing the same physical footprint and heater ratings, they exhibit slight differences in plate resistance, plate current, and screen grid current under typical operating conditions.

Direct Interelectrode Capacitances

Measured without an external shield, the capacitances of the tube are:

• Grid 1 to Plate (G1 to P): 0.34 pF to 0.6 pF (depending on construction variant)
• Input (G1 to H + K + G2 + G3): 16 pF
• Output (P to H + K + G2 + G3): 7.0 pF

Typical Operating Points

The following table outlines the typical operating characteristics of the 17JM6 and 17JM6A under different test conditions. In all cases, Grid 3 (beam plates) is tied to the cathode at the socket.

Note on Peak Knee measurements: These values are measured during a short interval (maximum of 2 seconds) using a recurrent waveform to prevent exceeding the maximum dissipation ratings of the grids and plate.

Cutoff and Triode Characteristics

• High-Voltage Cutoff (Condition A): At a plate voltage of 5,000 V and Grid 2 voltage of 150 V, the Grid 1 voltage required to reduce the plate current to 0.1 mA (or 1.0 mA depending on the test conditions) is approximately -100 V.
• Triode Amplification Factor: When triode-connected (Grid 2 tied to plate) with a plate and Grid 2 voltage of 150 V and Grid 1 voltage of -22.5 V, both the 17JM6 and 17JM6A exhibit an amplification factor (\mu) of 4.4.

Maximum Ratings

The maximum ratings of the 17JM6 and 17JM6A are defined under the Design-Maximum System for horizontal-deflection amplifier service:

• DC Plate-Supply Voltage (Boost + DC Power Supply): 770 V
• Peak Positive Pulse Plate Voltage: 6,500 V
• Peak Negative Pulse Plate Voltage: 1,500 V
• Positive DC Grid 3 (Beam Plate) Voltage: 70 V
• Grid 2 Voltage: 220 V
• Negative DC Grid 1 Voltage: 55 V (specifically rated for 17JM6A)
• Peak Negative Grid 1 Voltage: 330 V
• Plate Dissipation: 17.5 W
• Grid 2 Dissipation: 3.5 W
• DC Cathode Current: 175 mA
• Peak Cathode Current: 550 mA
• Grid 1 Circuit Resistance: 1.0 MΩ
• Bulb Temperature (at hottest point): 220 °C

Special Operating Conditions

1. Pulse Duty Cycle: For operation in a standard 525-line, 30-frame television system, the peak positive pulse plate voltage of 6,500 V is restricted to a duty cycle not exceeding 15% of one horizontal scanning cycle.
2. Grid-Leak Bias Protection: In stages operating with grid-leak bias, an adequate cathode-bias resistor or other protective means must be incorporated into the circuit. This protects the tube from excessive current and thermal runaway in the event that the drive excitation signal is lost.

Qualitative Curve Analysis

The plate characteristics of the 17JM6 family demonstrate a sharp knee transition occurring at low plate voltages, typically between 40 V and 70 V (specifically around 50 V to 60 V when Grid 1 is at 0 V). Above this knee, the plate current curves remain relatively flat, indicating high plate resistance and stable current delivery over a wide range of plate voltages.

The screen grid (Grid 2) current exhibits a sharp peak at very low plate voltages (below 50 V), where the plate is less effective at attracting electrons. As the plate voltage rises past the knee and exceeds the screen voltage, the Grid 2 current falls rapidly to a low, stable value (typically around 1.8 mA to 2.4 mA under Class A conditions).

Transfer characteristics show that both plate and screen currents rise smoothly as the Grid 1 voltage is made less negative (approaching 0 V). Higher screen voltages ($E_{c2}$) shift the transfer curves to the left, requiring a more negative Grid 1 voltage to achieve cutoff.

Related Designations and Comparisons

• 6JM6 / 6JM6A: The 17JM6 and 17JM6A are identical to the 6JM6 and 6JM6A, respectively, except for their heater ratings. The 6-volt versions utilize a 6.3 V heater, whereas the 17-volt versions are designed with a 16.8 V heater for series-string power supplies.
• 17JM6 vs. 17JM6A: The 17JM6A is an updated variant of the 17JM6. It features a slightly lower plate resistance (15,000 Ω vs. 18,000 Ω) and higher typical plate current (70 mA vs. 65 mA) under Class A conditions. Additionally, the 17JM6A has a slightly lower knee voltage (55 V vs. 60 V) and a higher peak Grid 2 current at the knee (30 mA vs. 27 mA).

Technical Summary

The 17JM6 and 17JM6A are Compactron beam-power pentodes designed for high-stress horizontal-deflection amplifier service in television receivers. Operating with a 16.8 V, 450 mA heater with an 11-second controlled warm-up time, these tubes are optimized for series-connected heater strings. They feature a maximum plate dissipation of 17.5 W, a peak positive pulse plate voltage rating of 6,500 V, and a peak cathode current rating of 550 mA. By providing separate external connections for the beam plates (Grid 3), the design minimizes snivets and allows for flexible circuit configuration.