15FY7 — Double Dissimilar Triode

The 15FY7 is a duodecar-type double dissimilar triode designed for use in television receivers. It is specifically engineered to function as a combined vertical-deflection oscillator and vertical-deflection amplifier, with its two triode sections optimized for these distinct roles.

Overview

The 15FY7 is a multi-electrode vacuum tube containing two highly dissimilar triode units within a single envelope. Triode Unit No. 1 is a high-mu triode designed to operate as a vertical-deflection oscillator, while Triode Unit No. 2 is a low-mu, high-current triode designed to serve as a vertical-deflection amplifier.

The tube is constructed using a Compactron T-9 glass envelope and utilizes a 12-pin button base. It is designed for series-string heater circuits in television receivers, featuring a controlled heater warm-up time. The 15FY7 is electrically identical to the 6FY7 and 11FY7 except for its heater voltage, current, and warm-up specifications.

Construction, Physical Dimensions, and Basing

The 15FY7 is housed in a T-9 glass bulb with a button 12-pin base (E12-70 designation). It requires a standard duodecar 12-contact socket for operation.

Physical Dimensions

• Maximum Diameter: 1.188 inches
• Maximum Seated Height: 2.500 inches
• Maximum Overall Height: 2.875 inches

Pin Connection Diagram (12EO Basing)

The 12EO basing arrangement provides independent connections for the electrodes of both triode sections, with the exception of the shared heater. The pin assignments, viewed from the bottom of the tube, are as follows:

Heater Characteristics and Ratings

The heater of the 15FY7 is designed for series-string operation with a controlled warm-up characteristic to minimize voltage surges in television receiver heater strings.

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 (Total DC and Peak)
• Heater Positive with Respect to Cathode: 100 V max (DC), 200 V max (Total DC and Peak)

Electrical Characteristics and Class A1 Operation

The two triode sections of the 15FY7 exhibit highly dissimilar electrical characteristics, reflecting their specialized roles in television deflection circuitry.

Triode Unit No. 1 (Oscillator Section)

Triode Unit No. 1 is a high-mu voltage amplifier. Under typical Class A1 operating conditions, it exhibits the following characteristics:

• Plate Voltage: 250 V
• Grid Voltage: -3.0 V
• Amplification Factor: 65
• Plate Resistance (Approx.): 40,500 ̩
• Transconductance: 1600 mhos
• Plate Current: 1.4 mA
• Grid Voltage (Approx.) for 30 A Plate Current: -5.5 V

Triode Unit No. 2 (Amplifier Section)

Triode Unit No. 2 is a low-mu, high-current power triode. It has two documented typical operating points:

*Note: Operating Point B is applied for a short interval (two seconds maximum) to prevent thermal damage to the tube.

Direct Interelectrode Capacitances

The unshielded direct interelectrode capacitances for each independent triode section are as follows:

Vertical-Deflection Service Ratings

When operated in a standard 525-line, 30-frame television scanning system, the 15FY7 must be operated within its Design-Maximum ratings. The requirements for the oscillator and amplifier sections differ significantly:

*The pulse duration must not exceed 15% of a scanning cycle (which corresponds to 2.5 milliseconds in a vertical scanning cycle). Some technical specifications describe this limit in the context of a horizontal scanning cycle.
**In stages operating with grid-leak bias, an adequate cathode-bias resistor or other protective means is required to protect the tube from excessive dissipation in the absence of excitation.
Note: Peak negative voltage limits of 400 V for Unit No. 1 and 250 V for Unit No. 2 are specified; these are variously designated as peak negative grid voltage or peak negative-pulse plate voltage in different technical specifications.

Related Designations

The 15FY7 belongs to a family of identical double dissimilar triodes that differ only in their heater configurations:

• 6FY7: Designed for standard parallel heater circuits, requiring a heater supply of 6.3 V at 1.05 A.
• 11FY7: Designed for series heater strings, requiring a heater supply of 11.0 V at 0.6 A (600 mA) with an average warm-up time of 11 seconds.
• 15FY7: Designed for series heater strings, requiring a heater supply of 14.7 V at 0.45 A (450 mA) with an average warm-up time of 11 seconds.

These three designations share identical physical dimensions, basing (12EO), interelectrode capacitances, and electrical operating characteristics for both triode units.

Technical Summary

The 15FY7 is a specialized duodecar double dissimilar triode designed for television vertical-deflection circuits. It integrates a high-mu oscillator triode (Unit No. 1, $\mu = 65$) and a low-mu power amplifier triode (Unit No. 2, $\mu = 6$) within a single Compactron T-9 envelope. Operating on a 14.7 V, 0.45 A heater with an 11-second controlled warm-up time, it is optimized for series-string television receivers. The tube features independent cathode connections and a 12-pin button base (12EO basing), allowing it to perform both oscillator and power amplification functions with minimal external components.