16AQ3 — Booster Diode Vacuum Tube

An indirectly heated, single-diode miniature vacuum tube designed for service as a booster or damper diode in the line-timebase circuits of transformerless television receivers.

Overview

The 16AQ3 (also designated as 16AQ3/XY88) is a high-voltage miniature diode designed specifically for television receiver applications. It functions as a booster or damper diode in line-timebase circuits, where it must withstand high peak voltages and carry substantial currents. The tube is characterized by its unipotential coated cathode, high heater-to-cathode voltage rating, and a 9-pin miniature construction with a top-cap connection.

The 16AQ3/XY88 is described as a 600 mA heater version of the 6AL3/EY88 damper diode. Additionally, it is closely related to the 20AQ3/LY88, which shares identical electrical characteristics and physical construction but utilizes a different heater rating.

Mechanical Construction and Pinout

The 16AQ3 is constructed in a miniature T-6½ glass envelope with a button 9-pin (E9-1) base. It features a top cap (C1-2) to provide high-voltage isolation for the cathode connection, which is critical for booster diode service where the cathode experiences high-voltage pulses. The tube requires a miniature 9-contact socket, corresponds to outline section 7D, and can be mounted in any position.

Physical Dimensions

• Maximum Diameter: 0.875 inches (7/8")
• Maximum Seated Height: 3.250 inches (3¼")
• Maximum Overall Height: 3.500 inches (3½")

Pin Connection Diagram (Basing 9CB)

The 16AQ3 uses the 9CB basing arrangement. When viewed from the bottom of the base, the pin connections are assigned as follows:

The multiple internally connected pins (Pins 1, 2, 3, 6, 7, and 8) must not be used as tie points for external circuit wiring to prevent internal breakdown or capacitive coupling.

Heater and Interelectrode Capacitances

The 16AQ3 features an indirectly heated, coated unipotential cathode. The heater is designed for series-string operation in transformerless television receivers.

Heater Specifications

• Heater Voltage (AC or DC): 16.4 V
• Heater Current: 0.6 A (600 mA)

For comparison, the identical 20AQ3/LY88 variant operates with a heater voltage of 20.2 V and a heater current of 0.45 A (450 mA).

Direct Interelectrode Capacitances

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

• Plate to all other elements: 8.6 pF
• Cathode to heater: 2.0 pF

Maximum Ratings and Operating Limits

The ratings for the 16AQ3 are established under the Design-Center Rating System. These limits represent the maximum values that the tube can safely withstand under typical operating variations.

Voltage and Current Limits

• Supply Voltage at Zero Current (Max.): 550 V
• Supply Voltage (Max.): 250 V
• Average Plate Current (Max.): 220 mA
• Peak Plate Current (Max.): 550 mA
• Plate Dissipation (Max.): 5 W
• Voltage Between Heater and Earth (Max.): 220 V r.m.s.

Pulsed and High-Voltage Limits

In line-timebase circuits, the booster diode is subjected to high-voltage pulses during horizontal retrace. The 16AQ3 is rated to handle these extreme conditions within specified duty cycle limits:

• Peak Negative-Pulse Plate Voltage (Max.): 6000 V
• Peak Heater-Cathode Voltage (Max.): 6600 V

These pulsed ratings are subject to strict timing constraints: the pulse duration must not exceed 22% of a single horizontal scanning cycle, with an absolute maximum duration of 18 microseconds. Under no circumstances should the absolute maximum plate voltage exceed 7500 V.

Technical Summary

The 16AQ3 (16AQ3/XY88) is a specialized miniature booster diode housed in a T-6½ envelope with a 9-pin button base and a top-cap cathode connection. Operating with a 16.4 V, 0.6 A heater, it is optimized for series-string transformerless television receivers. The tube is capable of handling an average plate current of 220 mA, a peak plate current of 550 mA, and a plate dissipation of 5 W. Its robust design allows it to withstand peak negative-pulse plate voltages of up to 6000 V (with an absolute limit of 7500 V) and peak heater-cathode voltages of up to 6600 V, making it highly suited for demanding horizontal damper service.