17JM6A — Compactron Beam Power Pentode

The 17JM6A (also designated as 17JM6-A) is a duodecar-type, compactron beam power pentode designed primarily for use as a horizontal-deflection amplifier in both color and black-and-white television receivers. It features a separate connection for its beam plates (Grid No. 3) to minimize "snivets" during television operation.

The 17JM6A is electrically identical to the 6JM6A except for its heater ratings. It is also unilaterally interchangeable with the 17JM6, from which it differs by incorporating a lower knee in its plate characteristics.

Construction, Physical Dimensions, and Pinout

The 17JM6A is constructed using a T12 glass bulb (Compactron T-12) and requires a duodecar 12-contact socket. The physical dimensions of the tube are as follows:

• Maximum Diameter: 1.563 inches
• Maximum Seated Height: 3.250 inches
• Maximum Overall Height: 3.625 inches

Depending on the specific manufacturing layout and outline configuration (such as Outlines 39A, 16A, or 12-79), three distinct pinout configurations are documented under the 12FJ basing designation.

Pinout Configuration A

In this configuration, the plate is connected internally to Pin 11:

• Pin 1: Heater (H)
• Pin 2: Cathode (K)
• Pin 3: Grid No. 2 (G2)
• Pin 4: Grid No. 3 (G3)
• Pin 5: Grid No. 1 (G1)
• Pin 6: No Connection (NC)
• Pin 7: No Connection (NC)
• Pin 8: Internal Connection (IC)
• Pin 9: No Connection (NC)
• Pin 10: Grid No. 3 (G3)
• Pin 11: Plate (P)
• Pin 12: Heater (H)

Pinout Configuration B

In this configuration, the plate is connected internally to Pin 7:

• Pin 1: Grid No. 1 (G1)
• Pin 2: Cathode (K)
• Pin 3: Grid No. 2 (G2)
• Pin 4: Grid No. 3 (G3)
• Pin 5: Heater (H)
• Pin 6: No Connection (NC)
• Pin 7: Plate (P)
• Pin 8: No Connection (NC)
• Pin 9: Internal Connection (IC)
• Pin 10: Grid No. 3 (G3)
• Pin 11: No Connection (NC)
• Pin 12: Heater (H)

Pinout Configuration C (Top Cap Plate Connection)

In this configuration, the plate is routed to a C1-3 top cap, and the base uses an E12-74 button 12-pin arrangement:

• Pin 1: Heater (H)
• Pin 2: Grid No. 3 (G3)
• Pin 3: Grid No. 2 (G2)
• Pin 4: Cathode (K)
• Pin 5: Grid No. 1 (G1)
• Pin 6: No Connection (NC)
• Pin 7: Internal Connection (IC)
• Pin 8: No Connection (NC)
• Pin 9: No Connection (NC)
• Pin 10: Grid No. 2 (G2)
• Pin 11: Grid No. 3 (G3)
• Pin 12: Heater (H)
• Top Cap: Plate (P)

Heater and Cathode Characteristics

The 17JM6A utilizes a coated unipotential cathode. The heater is designed for series-string television receiver applications and has the following ratings:

The average heater warm-up time is measured under specific conditions: applying four times the bogey heater voltage (67.2 V) to the heater in series with an external resistance equal to three times the bogey heater voltage divided by the bogey heater current (calculated as 3 * 16.8 V / 0.45 A = 112 ohms).

Heater-Cathode Voltage Limits

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

Electrical Characteristics and Class A1 Operation

Direct Interelectrode Capacitances

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

• Grid No. 1 to Plate: 0.6 pF
• Input (Grid No. 1 to Cathode, Heater, Grid No. 2, Grid No. 3): 16 pF
• Output (Plate to Cathode, Heater, Grid No. 2, Grid No. 3): 7 pF

Typical Operating Conditions

The 17JM6A can be operated in either pentode or triode configurations. In pentode operation, Grid No. 3 is connected directly to the cathode at the socket.

Note: Values marked with an asterisk are measured using a recurrent waveform method to avoid exceeding the maximum ratings of the tube.

Instantaneous Plate Knee Values

At the knee of the plate characteristic curve, under the conditions of Eb = 55 V, Ec2 = 150 V, and Ec1 = 0 V, the instantaneous currents are:

• Plate Current (Ib): 345 mA
• Grid No. 2 Current (Ic2): 30 mA

Horizontal-Deflection Amplifier Service and Ratings

The primary application of the 17JM6A is in the horizontal-deflection amplifier stage of television receivers operating under a 525-line, 30-frame system. The following design-maximum ratings must be observed:

Circuit Protection

The peak positive-pulse plate voltage rating of 6500 V is restricted to a maximum pulse duration of 15% of one horizontal scanning cycle (equivalent to 10 s in a standard 525-line, 30-frame system).

Additionally, because horizontal-deflection stages often operate with grid-leak bias, the tube requires an adequate cathode bias resistor or other protective means to limit plate and screen currents and prevent thermal runaway in the event that excitation is lost.

Qualitative Curve Observations

The average plate characteristics of the 17JM6A, when plotted for Ec1 = 0 V at a 10% duty cycle, reveal several key performance traits:

• Knee Behavior: The plate current (Ib) curves exhibit a very sharp knee at low plate voltages, typically between 50 V and 75 V depending on the screen grid voltage (Ec2). This low-knee characteristic is a key design improvement over the original 17JM6, allowing for more efficient operation.
• High-Current Capability: For Ec2 = 200 V, the plate current reaches approximately 580 mA above the knee.
• Screen Grid Current Behavior: The Grid No. 2 current (Ic2) peaks sharply at very low plate voltages below the knee. Once the plate voltage rises past the knee, the screen current drops rapidly to a low, stable level below 50 mA, minimizing screen grid dissipation during normal operation.

Technical Summary

The 17JM6A is a high-performance compactron beam power pentode designed for television horizontal-deflection service. Operating with a 16.8 V, 0.45 A heater, it features a separate beam plate connection to suppress snivets and a low-knee plate characteristic for high efficiency. With a peak positive-pulse plate voltage rating of 6500 V, a plate dissipation limit of 17.5 W, and a transconductance of 7,300 mhos under typical Class A1 conditions, the 17JM6A provides robust and reliable operation in demanding television deflection circuits.