13GF7A — Dissimilar Double Triode

The 13GF7A (also designated as 13GF7-A) is a Novar-type dissimilar double triode designed for use in television receivers as a combined vertical-deflection oscillator and vertical-deflection amplifier. It contains two electrically independent, highly distinct triode units within a single T-9 glass envelope. Unit No. 1 is a high-mu triode intended for service as a vertical-deflection oscillator, while Unit No. 2 is a low-mu, high-perveance triode designed to operate as a vertical-deflection amplifier.

Construction, Physical Dimensions, and Basing

The 13GF7A is constructed using a T-9 glass bulb and features a 9-pin Novar button base (E9-89 designation) with a 0.687-inch pin circle. The physical construction includes an exhaust tip located on the base of the tube.

The physical dimensions of the tube are:

• Maximum Diameter: 1.188 inches
• Maximum Seated Height: 2.000 inches
• Maximum Overall Height: 2.380 inches

The tube requires a standard novar 9-contact socket. The basing arrangement is designated as 9QD, which provides the following pin connections (viewed from the bottom of the tube):

The cathodes of both triode units are coated unipotential types. They are electrically independent, allowing separate biasing and circuit configurations for the oscillator and amplifier sections.

Heater Characteristics and Ratings

The heater of the 13GF7A is designed for series-string operation in television receivers. It has controlled warm-up characteristics to ensure reliable operation in series circuits.

Calculations and Design Considerations

• Heater Power Calculation: Using the nominal voltage of 13.0 V and nominal current of 0.45 A, the calculated heater power is: $13.0\text{ V} \times 0.45\text{ A} = 5.85\text{ W}$
• Warm-up Time Definition: The average heater warm-up time of 11 seconds is defined as the time required for the voltage across the heater to reach 80% of its bogey value (10.4 V) when 4 times the bogey heater voltage (52.0 V) is applied to a circuit consisting of the heater in series with a resistance equal to 3 times the bogey heater resistance. This series resistance is calculated as: $3 \times \frac{13.0\text{ V}}{0.45\text{ A}} = 86.67\ \Omega$

Equipment designers must design the receiver circuitry so that the heater current is centered at the bogey value of 0.45 A, with supply variations restricted to maintain the current within the specified 0.030 A tolerance.

Interelectrode Capacitances

The direct interelectrode capacitances of the two dissimilar triode units are approximately as follows (measured without an external shield):

The higher capacitances of Unit No. 2 reflect its larger, high-perveance structure designed for power amplification.

Class A1 Amplifier Characteristics

The two triode units exhibit highly dissimilar electrical characteristics, optimized for their respective roles. Typical Class A1 operating points and characteristics for each unit are:

Additional Operating Characteristics

• Unit No. 1 Cutoff: The grid voltage required to reduce the plate current to approximately 10 $\mu$A is -5.5 V.
• Unit No. 2 Cutoff: The grid voltage required to reduce the plate current to approximately 100 $\mu$A is -45 V.
• Unit No. 2 Peak Current Capability: At a plate voltage of 60 V and zero grid voltage, Unit No. 2 conducts a plate current of 95 mA. At a grid voltage of -28 V, the plate current is 10 mA.

Vertical-Deflection Service Ratings

The 13GF7A is rated under the Design-Maximum system for operation in a 525-line, 30-frame television system. The maximum ratings for each unit in this service are:

This is an Absolute Maximum rating. The pulse duration must not exceed 15% of a vertical scanning cycle (equivalent to 2.5 milliseconds).

Maximum Circuit Values

• Grid-Circuit Resistance: For either grid-resistor-bias or cathode-bias operation, the maximum allowable grid-circuit resistance is 2.2 megohms for both Unit No. 1 and Unit No. 2.

Related Designations and Curves

The 13GF7A is part of a family of identical-characteristic tubes with different heater ratings, which includes the 6GF7A (6.3 V, 0.985 A) and the 10GF7A (9.7 V, 0.6 A). These "A" suffix versions are identical to the older 6GF7, 10GF7, and 13GF7 except for their physical construction, which features a shorter bulb and an exhaust tip on the base.

For average plate characteristic curves, designers are directed to refer to the curves of the 6DR7 (for Unit No. 1) and the 6EM7 (for Unit No. 2), as the electrical characteristics of the respective units are identical to those types.

Technical Summary

The 13GF7A is a Novar-type, dissimilar double triode designed for television vertical-deflection applications. It integrates a high-mu oscillator triode (Unit No. 1, $\mu = 64$) and a low-mu, high-perveance power amplifier triode (Unit No. 2, $\mu = 5.4$) in a single T-9 envelope. Operating from a 13 V, 0.45 A series-string heater with controlled warm-up, the tube provides a compact and efficient solution for vertical deflection circuits in both color and black-and-white television receivers.