19AU4GTA — Half-Wave Damper Diode

The 19AU4GTA (also designated as 19AU4-GTA) is an indirectly heated, half-wave rectifier diode designed specifically for damper service in the horizontal deflection circuits of television receivers. It is engineered to operate in both black-and-white and color television systems, withstanding high-voltage pulses of line frequency between its cathode and both its heater and plate elements. This makes it highly suitable for "direct drive" horizontal deflection topologies.

Relationship to Other Types

The 19AU4GTA belongs to the 19AU4 family of tubes. It is electrically identical to the standard 19AU4 except for its current-handling capabilities: the 19AU4GTA features a higher maximum DC output current of 190 mA (compared to 175 mA for the 19AU4) and a higher peak plate current of 1150 mA (compared to 1050 mA).

Additionally, the 19AU4GTA is identical to the 6AU4-GTA except for its heater ratings and the inclusion of a controlled heater warm-up characteristic.

Construction, Heater, and Base Connection

The 19AU4GTA is constructed with a coated unipotential cathode housed in a T-9 glass envelope. It features a short intermediate shell octal base, which can be either a 5-pin (B5-85) or 6-pin (B6-60) configuration. The tube can be mounted and operated in any position.

Physical Dimensions

• Maximum Bulb Diameter: 1-3/16 inches (1.188 inches)
• Maximum Base Diameter: 1-9/32 inches
• Maximum Seated Height: 3-1/4 inches (3.250 inches)
• Maximum Overall Length: 3-13/16 inches (3.813 inches)

Heater Specifications

The heater is designed for series-connected heater strings drawing a nominal current of 600 mA. It features a controlled warm-up characteristic to minimize voltage surges across other tubes in the series string.

• Heater Voltage (AC or DC): 18.9 V
• Heater Current: 0.6 A (600 mA) ± 6%
• Heater Warm-up Time: Approximately 11.0 seconds

The warm-up time is defined as the time required to reach 80% of the rated heater voltage when four times the rated voltage is applied in series with an external resistance equal to three times the nominal heater operating resistance (or three times the rated voltage divided by the rated current).

Pinout and Wiring Constraints

The tube utilizes the 4CG basing diagram. Viewed from the bottom of the base, the pin connections are as follows:

Important Installation Note: Socket terminals for pins 1 (if present), 2, 4, and 6 must not be used as circuit tie points. Unused pins on the socket should be tied directly to the heater.

Interelectrode Capacitances

The direct interelectrode capacitances of the 19AU4GTA vary slightly depending on the measurement conditions. These values are measured without an external shield:

Standard Unshielded Conditions

• Heater to Cathode (H to K): 4.0 pF
• Plate to Cathode and Heater (P to H+K): 8.5 pF
• Cathode to Plate and Heater (K to P+H): 11.5 pF

Alternative Conditions (Unused Pins Tied to Heater)

• Heater to Cathode (H to K): 3.2 pF
• Plate to Cathode and Heater (P to H+K): 7.0 pF
• Cathode to Plate and Heater (K to P+H): 10.0 pF

Maximum Ratings

The maximum ratings for the 19AU4GTA are established under the Design Center and Design Maximum systems. These ratings are critical for ensuring reliable operation in high-stress television deflection environments.

Operating Conditions for Damper Ratings

The maximum ratings for damper service are specified for operation in a standard 525-line, 30-frame television system. Under these conditions, the duty cycle of the horizontal voltage pulse must not exceed 15% of one horizontal scanning cycle. Power rectification service is explicitly not recommended for this tube.

Typical Characteristics and Operating Points

Under typical operating conditions, the 19AU4GTA exhibits a low internal voltage drop when conducting.

• Average Tube Voltage Drop: 25 Volts (measured with the tube conducting a plate current of 350 mA)

90° Deflection Scan System Example

In a typical application within a 90° deflection scan system, the tube operates under the following conditions:

• Peak Inverse Plate Voltage: 3.65 kV
• Peak Heater-Cathode Voltage: 3.9 kV
• Average Cathode Current: 120 mA
• Peak Cathode Current: 500 mA
• Boosted B+ Voltage: 640 V
• Plate Dissipation: 2.8 W
• Average Tube Voltage Drop (at 350 mA): 25 V

Plate Characteristics and Curves

The plate characteristics of the 19AU4GTA describe the relationship between plate current and plate voltage at the rated heater voltage of 18.9 V.

The average characteristic curve is non-linear, starting at 0 V and 0 mA. The conduction profile shows the following qualitative and quantitative points:

• At a plate potential of approximately 10 V, the plate current reaches 100 mA (the curve is solid up to approximately 125 mA at 10 V).
• At a plate potential of 30 V, the plate current rises to approximately 480 mA.
• Above 125 mA, the characteristic curve is typically represented as dashed, indicating peak or pulsed operation regions.
• At 50 V plate potential, the current reaches 1000 mA.
• At 55 V plate potential, the current reaches approximately 1160 mA.

Technical Summary

The 19AU4GTA is a specialized, indirectly heated half-wave diode designed for television horizontal damper service. Operating with an 18.9 V, 600 mA heater with controlled warm-up, it is optimized for series-connected heater strings. The tube features a T-9 glass envelope with a 5-pin or 6-pin octal base and is rated for a peak inverse plate voltage of 4500 V, a maximum DC plate current of 190 mA, and a plate dissipation of 6.0 W. Its high heater-to-cathode voltage rating (up to 4500 V peak) allows it to withstand the severe pulse stresses typical of horizontal deflection circuits in color and monochrome television receivers.