17D4 — Half-Wave Vacuum Rectifier and Damper Diode

The 17D4 is an indirectly heated, half-wave vacuum rectifier designed specifically for service as a damping diode in the horizontal deflection circuits of television receivers. It is engineered for use in series-connected heater strings, featuring controlled thermal characteristics to minimize heater voltage surges during the receiver's warm-up cycle.

Mechanical Specifications and Pinout

The 17D4 is constructed in a glass bulb with a T-9 outline (JEDEC 9-41 or 13D outline designation). It features an 8-pin octal base, which can be an intermediate shell (B5-85 or JETEC B6-8) or a short intermediate shell (B6-60). The tube can be mounted in any position.

Physical Dimensions

• Maximum Diameter: 1-3/16 inches to 1-9/32 inches
• Maximum Seated Height: 2-3/4 inches
• Maximum Overall Length: 3-5/16 inches

Pin Connections

The tube utilizes the JEDEC 4CG bottom-view basing diagram. The pin assignments are as follows:

To ensure proper operation and safety, all unused pins and associated metal parts must be tied directly to the heater. Socket terminals corresponding to pins 1, 2, 4, and 6 must never be utilized as circuit tie points.

Heater Characteristics and Controlled Warm-up

The heater of the 17D4 is designed to operate in series with other heaters of similar current ratings in television receivers.

• Heater Voltage (AC or DC): 16.8 V
• Heater Current: 0.45 A (with a tolerance of ±0.030 A)
• Average Heater Warm-up Time: 11.0 seconds

The controlled warm-up characteristic is specifically designed to prevent voltage surges across individual heaters in a series string. The warm-up time is defined as the time required for the voltage across the heater to reach 80% of its rated value (13.44 V) when four times the rated heater voltage (67.2 V) is applied to a circuit consisting of the tube heater in series with an external resistance equal to three times the nominal heater operating resistance. The nominal operating resistance is calculated as the rated heater voltage divided by the rated heater current.

Electrical Characteristics and Typical Operation

The 17D4 exhibits low internal resistance, resulting in a low voltage drop during conduction. Under typical operating conditions, the tube voltage drop is between 21 and 22 volts when measured at a plate current ($I_b$) of 250 mA.

Direct Interelectrode Capacitances

The capacitances of the tube, measured with unused pins and metal parts tied to the heater, are approximately:

• Heater to Cathode: 3.0 pF
• Plate to Cathode and Heater: 6.0 pF
• Cathode to Plate and Heater: 8.0 pF

Average Plate Characteristics

The relationship between plate current ($I_b$) and plate voltage ($E_b$) under rated heater conditions is characterized by the following typical operating points:

• At $E_b = 10\text{ V}$, the plate current is approximately 80 mA.
• At $E_b = 20\text{ V}$, the plate current is approximately 220 mA.
• At $E_b = 30\text{ V}$, the plate current is approximately 420 mA.
• At $E_b = 40\text{ V}$, the plate current is approximately 650 mA.
• At $E_b = 50\text{ V}$, the plate current is approximately 900 mA.

Maximum Ratings and Operating Conditions

The maximum ratings of the 17D4 are defined under the Design-Maximum System. These ratings apply to damper service in a standard 525-line, 30-frame television system, where the duty cycle of the horizontal voltage pulse does not exceed 15% of one scanning cycle (or a maximum duration of 10 microseconds).

To prevent overheating and ensure reliable operation, the tube must be provided with adequate ventilation.

Related Designations and Equivalents

The 17D4 is electrically identical to the 6DA4 and 12D4 vacuum tubes, except for its specific heater ratings. The 6DA4 and 12D4 are designed for different heater supply configurations, whereas the 17D4 is optimized for 450 mA series-connected heater strings. These designations cannot be directly substituted without adjusting the heater supply circuitry to match the required voltage and current specifications.

Technical Summary

The 17D4 is an octal-based, indirectly heated half-wave rectifier and damper diode housed in a T-9 glass envelope. It is designed for series-heater television receiver circuits, operating at a nominal heater rating of 16.8 V and 0.45 A with a controlled 11-second warm-up time. The tube features a maximum peak inverse voltage rating of 4,400 V, a peak plate current capability of 900 mA, and a maximum plate dissipation of 5.5 W. Its low internal voltage drop of 21 to 22 V at 250 mA makes it highly efficient for horizontal deflection damping applications.