10DA7 — Dissimilar Double Triode Vacuum Tube

The 10DA7 is a miniature 9-pin double triode containing two highly dissimilar triode sections in a single envelope. It is specifically designed for television receiver applications, combining a medium-mu triode (Section 1) intended for vertical oscillator service with a high-dissipation, low-mu triode (Section 2) intended for vertical deflection amplifier service. This integration allows the tube to perform both the oscillation and high-current output amplification functions required for the vertical sweep of large 90° picture tubes.

Mechanical Specifications and Pinout

The 10DA7 is constructed in a T-6 1/2 glass envelope with a miniature button 9-pin base (designation 9EF). The physical dimensions of the tube are compact, allowing for space-efficient layout designs in television chassis.

The 9EF base connection layout, viewed from the bottom of the tube, assigns separate pins to each electrode of the two independent triode sections, with the exception of the heater:

• Pin 1: Plate (Section 1)
• Pin 2: Control Grid (Section 1)
• Pin 3: No Connection (NC)
• Pin 4: Heater
• Pin 5: Heater
• Pin 6: Plate (Section 2)
• Pin 7: Control Grid (Section 2)
• Pin 8: Cathode (Section 2)
• Pin 9: Cathode (Section 1)

This configuration ensures that the two triodes remain electrically independent, allowing them to operate at different bias levels and in separate circuit stages.

Heater and Warm-Up Characteristics

The 10DA7 features a coated unipotential cathode structure heated by a series-string compatible heater. The heater is designed with a controlled warm-up time to ensure reliable operation in series-connected heater strings.

The heater warm-up time is defined under specific test conditions: the time required for the voltage across the heater to reach 80% of its rated voltage (8.4 V) after applying four times the rated heater voltage (42.0 V) to a circuit consisting of the tube heater in series with an external resistance equal to three times the nominal heater operating resistance.

Heater-Cathode Voltage Ratings

To prevent insulation breakdown between the heater and the independent cathodes, the following maximum voltage limits must be observed:

• Heater Negative with respect to Cathode: 200 V max.
• Heater Positive with respect to Cathode: 200 V max (with the DC component restricted to a maximum of 100 V).

Electrical Characteristics and Typical Operating Points

The two sections of the 10DA7 are optimized for entirely different roles, resulting in highly contrasting electrical characteristics under typical Class A operating conditions.

Cutoff and Zero-Bias Characteristics

• Section 1 Cutoff: The control-grid voltage required to reduce plate current to 50 µA (at transconductance of 30 µmhos) is approximately -16.5 V.
• Section 2 Cutoff: The control-grid voltage required to reduce plate current to 0.5 mA is approximately -42 V.
• Section 2 Zero-Bias Plate Current: At a plate voltage of 60 V and zero grid bias, Section 2 conducts a high plate current of 80 mA, demonstrating its capability to deliver the high peak currents necessary for vertical deflection.

Maximum Ratings

The maximum ratings for the 10DA7 are established under the Design Center System. These limits must not be exceeded under the worst-case operating conditions of supply voltage variation, component tolerances, and signal modulation.

The peak pulse ratings (such as the 1,800 V peak positive plate pulse and the -400 V peak negative grid pulse) are specified for operation in a standard 525-line, 30-frame television system. For these pulse ratings to apply, the duty cycle of the voltage pulse must not exceed 15% of one scanning cycle.

Direct Interelectrode Capacitances

Because the two triode sections are housed in close proximity within a single miniature envelope, interelectrode capacitances are critical design considerations to prevent unwanted coupling or feedback. The capacitances are measured without an external shield:

The larger capacitances of Section 2 reflect its physically larger electrode structure, which is designed to handle higher current and plate dissipation.

Similar Types and Design Comparisons

The 10DA7 is closely related to other television deflection double triodes. Specifically, except for its heater ratings and controlled heater warm-up time, the 10DA7 is identical to the 6DA7 (which may also appear in historical references as the 6AD7). While the 6DA7 is designed for standard 6.3 V parallel heater circuits, the 10DA7 is tailored for 10.5 V series-string television receivers where controlled warm-up characteristics are mandatory to prevent heater voltage surges during receiver power-up.

Technical Summary

The 10DA7 is a specialized, miniature 9-pin dissimilar double triode designed for vertical deflection circuits in television receivers. It features a 10.5 V, 0.6 A heater with a controlled 11.0-second warm-up time. Section 1 is a medium-mu triode ($\mu = 20$) optimized for vertical oscillator service, while Section 2 is a low-mu, high-dissipation triode ($\mu = 6.3$, plate dissipation of 6.0 W) capable of handling peak positive plate pulses up to 1,800 V for vertical amplifier service. This combination allows a single tube to drive the vertical sweep of large 90° picture tubes, reducing component count and chassis space.