17JF6 — Novar Beam Power Tube

The 17JF6 is a beam power tube of the Novar design, primarily intended for use as a horizontal-deflection amplifier in black-and-white television receivers operating on a 525-line, 30-frame system. It is engineered to deliver high peak plate currents at low plate voltages, featuring a sharp knee in its plate characteristics and robust power handling capabilities. The 17JF6 is electrically identical to the 6JF6 and 22JF6 except for its heater ratings.

Construction, Heater, and Base Pinout

The 17JF6 features a Novar construction, requiring a standard 9-contact novar socket. The tube is housed in an envelope corresponding to outline 18E or 18F.

The heater is designed for series-string or parallel operation, with the following ratings:

• Heater Voltage (AC or DC): 16.8 V at a current of 0.600 A
• Heater Current: 0.600 ± 0.040 A
• Average Heater Warm-up Time: 11 seconds
• Heater-Cathode Voltage Limits:
  • Peak value: ±200 V maximum
  • Average value: 100 V maximum

Heater Power Calculation

The nominal heater power consumption can be calculated as follows: $\text{Heater Power} = \text{Heater Voltage} \times \text{Heater Current}$ Using the nominal inputs of 16.8 V and 0.6 A: $\text{Heater Power} = 16.8\text{ V} \times 0.6\text{ A} = 10.08\text{ W}$

The tube utilizes the 9QL pinout configuration, which provides the following connections when viewed from the bottom of the base:

Direct Interelectrode Capacitances

The approximate direct interelectrode capacitances of the 17JF6, measured without an external shield, are:

• Grid No. 1 to Plate: 1.2 pF
• Grid No. 1 to Cathode, Heater, Grid No. 2, and Grid No. 3: 22 pF
• Plate to Cathode, Heater, Grid No. 2, and Grid No. 3: 9 pF

Electrical Characteristics and Operating Points

The 17JF6 can be operated in both triode and pentode configurations. The typical characteristics under Class A1 amplifier conditions are detailed below.

Triode Connection

In this configuration, Grid No. 2 is connected to the plate at the socket, and Grid No. 3 is connected to the cathode at the socket.

• Plate Voltage: 125 V
• Grid No. 2 Voltage: 125 V
• Grid No. 1 Voltage: -20 V
• Triode Amplification Factor (μ): 4.1

Pentode Connection

In this configuration, Grid No. 3 is connected directly to the cathode at the socket.

*Note: Measured using a recurrent waveform to prevent exceeding maximum dissipation limits during testing.

Horizontal-Deflection Amplifier Service

When used in horizontal-deflection amplifier service for 525-line, 30-frame television receivers, the 17JF6 must be operated within strict design-maximum ratings to ensure reliability.

Design-Maximum Ratings

• DC Plate Supply Voltage: 770 V
• Peak Positive-Pulse Plate Voltage: 6,500 V (with a pulse duration not exceeding 15% of the horizontal scanning cycle, or 10 µs)
• Peak Negative-Pulse Plate Voltage: 1,500 V
• DC Grid-No. 3 Voltage: 100 V (a positive bias up to a typical value of 50 V may be applied to minimize "snivets" interference)
• DC Grid-No. 2 Voltage: 220 V
• Peak Negative-Pulse Grid-No. 1 Voltage: 330 V
• Peak Cathode Current: 950 mA
• Average Cathode Current: 275 mA
• Grid-No. 2 Input: 3.5 W
• Plate Dissipation: 17 W (measured using a recurrent waveform)
• Maximum Bulb Temperature (at hottest point): 240 °C

Maximum Circuit Values

To prevent thermal runaway and protect the tube, the Grid-No. 1 circuit resistance must not exceed the following limits depending on the biasing method:

• Cathode-bias operation: 1.0 MΩ
• Grid-leak-bias operation: 10 MΩ
• Fixed-bias operation: 0.47 MΩ

A bias resistor or other protective means is strictly required to safeguard the tube in the event that excitation is lost.

Curve Observations and Behavior

The plate characteristics of the 17JF6 demonstrate its suitability for high-efficiency deflection service:

• Knee Characteristics: At a constant Grid No. 2 voltage of 125 V, the plate current ($I_b$) curves exhibit a sharp knee occurring between 50 V and 75 V plate voltage. This sharp transition allows for efficient switching and minimizes power loss in deflection circuits.
• Peak Current Capability: At $E_{[c1](/tubes/C1)} = 0\text{ V}$ and $E_{c2} = 125\text{ V}$, the plate current peaks near 800 mA at a plate voltage of 100 V. When the screen voltage ($E_{c2}$) is increased, the peak plate current rises significantly, exceeding 1,000 mA at $E_{c2} = 175\text{ V}$.
• Screen Grid Behavior: The Grid No. 2 current ($I_{c2}$) rises sharply at low plate voltages, peaking near 100 mA at $E_b = 0\text{ V}$ when $E_{[c1](/tubes/C1)} = 0\text{ V}$.
• Screen Voltage Influence: Varying the screen voltage ($E_{c2}$) from 50 V to 175 V demonstrates that higher screen voltages shift the knee voltage upward while substantially increasing the available peak plate current.

Related Designations

The 17JF6 is part of a family of closely related beam power tubes. It is identical in its internal structure, electrode configuration, and electrical characteristics to the 6JF6 and 22JF6. These types differ solely in their heater ratings, allowing designers to select the appropriate version depending on whether the receiver uses a 6.3 V parallel heater supply, a 17 V series string, or a 22 V series string. Unrestricted substitution between these types is not possible without modifying the heater supply circuit.

Technical Summary

The 17JF6 is a Novar-type beam power tube designed for high-current, low-voltage applications, specifically horizontal-deflection amplifier service in television receivers. It features a 16.8 V, 0.6 A heater with a controlled 11-second warm-up time. Under typical pentode operating conditions, it exhibits a transconductance of 10,000 µmhos and a plate resistance of approximately 12,000 Ω. Its design-maximum ratings include a peak positive-pulse plate voltage of 6,500 V and a plate dissipation of 17 W, making it a robust and reliable choice for demanding deflection circuits when operated within its specified limits.