17AY3A — Half-Wave Vacuum Rectifier

The 17AY3A is a Novar-type half-wave vacuum rectifier designed specifically for use as a damper diode in the horizontal-deflection circuits of television receivers, particularly black-and-white television systems. It features a coated unipotential cathode and is housed in a compact T-9 glass envelope with a 9-pin button base.

The tube is electrically identical to the 6AY3B and 12AY3A except for its heater ratings. It is also closely related to the 6AY3, 6AY3A, 12AY3, and 17AY3 families, from which it differs physically by having a shorter bulb and a base equipped with an exhaust tip at the bottom. As a power-handling device, the 17AY3A requires adequate ventilation during operation to ensure reliable performance and prevent thermal overload.

Construction, Physical Dimensions, and Base

The 17AY3A is constructed in a T-9 glass envelope with a Novar button 9-pin base (E9-89 designation) featuring an exhaust tip at the bottom. This physical configuration results in a shorter bulb than some of its predecessor types.

Physical Dimensions

• Maximum Diameter: 1.188 inches
• Maximum Seated Height: 2.625 inches
• Maximum Overall Height: 3.005 inches

Socket and Wiring Requirements

The tube requires a standard Novar 9-contact socket. A critical wiring caution applies to the socket terminals: pins 1, 3, 6, and 8 are designated as Internal Connections (IC) and must never be used as tie points for external circuit wiring.

Pinout Configurations (9HP Basing Diagram)

The technical literature contains two variations for the 9HP basing diagram connections. In both configurations, pins 1, 3, 6, and 8 are reserved as Internal Connections, and pin 9 is connected to the cathode. The heater and plate connections differ as follows:

Heater Characteristics and Design Requirements

The 17AY3A is designed for series heater string operation or dedicated AC/DC supplies.

Heater Ratings

• Heater Voltage (AC or DC): 16.8 V (at the bogey current of 0.45 A)
• Heater Current: 0.45 A (with a tolerance of 0.03 A)
• Average Heater Warm-up Time: 11 seconds

Heater Design and Warm-up Definition

Equipment utilizing the 17AY3A must be designed so that the heater current is centered at the specified bogey value of 0.45 A. Variations in the heater supply must be restricted to keep the operating current within the 0.03 A tolerance.

The average heater warm-up time of 11 seconds is defined under specific test conditions: it is the time required for the voltage across the heater to reach 80% of its bogey value (13.44 V) when 4 times the bogey heater voltage (67.2 V) is applied to a circuit consisting of the tube heater in series with a resistance equal to:

$\text{Resistance} = \frac{3 \times V_{\text{bogey}}}{I_{\text{bogey}}} = \frac{3 imes 16.8\text{ V}}{0.45\text{ A}} = 112\ \Omega$

This calculation uses the nominal bogey voltage of 16.8 V and the nominal bogey current of 0.45 A as inputs to determine the series test resistance of 112 ohms.

Electrical Characteristics and Capacitances

The 17AY3A exhibits low internal voltage drop and moderate interelectrode capacitances, typical of a high-efficiency damper diode.

Typical Operating Characteristics

• Tube Voltage Drop: 32 V (measured instantaneously at a plate current of 350 mA)

Direct Interelectrode Capacitances (Unshielded, Approximate)

• Plate to Cathode and Heater: 6.5 pF
• Cathode to Plate and Heater: 9.0 pF
• Heater to Cathode: 2.8 pF

Maximum Ratings (Design-Maximum System)

The ratings for the 17AY3A are specified under the Design-Maximum Rating System for operation in a 525-line, 30-frame television system. These values represent the limits within which the tube must be operated to ensure reliable service.

Damper Service Limits

• Peak Inverse Plate Voltage: 5000 V maximum (The pulse duration must not exceed 15% of a horizontal scanning cycle, or a maximum of 10 microseconds).
• Peak Plate Current (Steady State): 1100 mA maximum
• Average Plate Current (DC): 175 mA maximum
• Plate Dissipation: 6.3 W to 6.5 W maximum

Heater-Cathode Voltage Ratings

Due to the high-voltage pulses present in horizontal-deflection circuits, the heater-cathode insulation is rated to withstand significant potential differences:

• Heater Negative with Respect to Cathode:
  • DC Limit: 900 V
  • Total DC and Peak Limit: 5000 V
• Heater Positive with Respect to Cathode:
  • DC Limit: 100 V
  • Total DC and Peak Limit: 300 V to 800 V

Technical Summary

The 17AY3A is a Novar-type, half-wave vacuum rectifier designed for television damper service in horizontal-deflection circuits. Operating with a 16.8 V, 0.45 A heater, it features an average warm-up time of 11 seconds and is housed in a compact T-9 envelope with a 9-pin button base featuring an exhaust tip. It is characterized by a low 32 V instantaneous drop at 350 mA, a peak inverse voltage rating of 5000 V, and a peak plate current capability of 1100 mA. Proper circuit design requires strict adherence to the 15% pulse duty cycle limit and avoiding the use of pins 1, 3, 6, and 8 as tie points.