15EA7 — Dissimilar Double Triode

The 15EA7 is a glass-envelope, octal-base, dissimilar double triode designed primarily for use in television receivers. It is engineered to perform two distinct roles within a single envelope: Section One operates as a high-mu vertical-deflection oscillator, while Section Two serves as a low-mu, high-perveance vertical-deflection amplifier.

Except for its heater ratings and heater warm-up characteristics, the 15EA7 is electrically and structurally identical to the 6EA7 (and the combined 6EM7/6EA7 designation).

Physical Specifications and Basing

The 15EA7 is constructed with a T-9 glass bulb and utilizes an intermediate-shell 8-pin octal base (classified under designations B8-6 or B8-251). The tube can be mounted and operated in any physical position.

Physical Dimensions

• Maximum Diameter: 1.281 inches (approx. 1-9/32 inches)
• Maximum Seated Height: 2.439 inches (approx. 2-7/16 inches)
• Maximum Overall Height: 3.000 inches (approx. 3 inches)

Pin Connections (JEDEC 8BD Basing Diagram)

The 8BD basing arrangement provides independent connections for the two triode sections, viewed from the bottom of the base:

Heater Characteristics

The 15EA7 features a coated unipotential cathode structure. The heater is designed for series-string television receiver applications and can be operated on either AC or DC.

• Nominal Heater Voltage: 14.8 V (at bogey heater current). Note: Some general tables group the 15EA7 with the 13EM7 under a 13 V heading, but specific registrations establish 14.8 V as the standard.
• Nominal Heater Current: 0.45 ± 0.03 A (450 mA)
• Average Heater Warm-up Time: 11 seconds

Heater Warm-up Time Definition and Calculation

The heater warm-up time is defined as the time required for the voltage across the heater to reach 80% of its rated value after applying four times the rated heater voltage to a circuit consisting of the tube heater in series with a resistance equal to three times the rated heater voltage divided by the rated heater current.

Using the nominal ratings ($V_h = 14.8\text{ V}$ and $I_h = 0.45\text{ A}$), the required series resistance ($R_{series}$) is calculated as: $R_{series} = 3 \times \frac{14.8\text{ V}}{0.45\text{ A}} \approx 98.7\ \Omega$

Heater-Cathode Voltage Ratings (Design-Maximum System)

• Heater Positive with Respect to Cathode:
  • DC Component: 100 V max
  • Total DC and Peak: 200 V max
• Heater Negative with Respect to Cathode:
  • Total DC and Peak: 200 V max

For series heater operation, equipment designers must ensure that the heater current is centered at the specified bogey value of 0.45 A, with supply variations restricted to maintain the current within specified tolerances.

Electrical Characteristics and Typical Operating Points

The two triode sections of the 15EA7 exhibit highly dissimilar characteristics. Section One is a high-mu voltage amplifier/oscillator, whereas Section Two is a low-mu, high-perveance power amplifier.

For the average plate characteristics of Section One, designers can refer to the curves of the 6DR7 (Unit No. 1).

Typical Class A1 Operating Conditions

Special Operating Points

• Section Two Instantaneous Zero-Bias Values: At a plate voltage ($E_b$) of 60 V and grid voltage ($E_c$) of 0 V, the instantaneous plate current ($I_b$) is 100 mA (or 95 mA under alternative typical conditions).
• Section Two Cutoff Characteristics: At a plate voltage of 150 V, a grid voltage of -28 V reduces the plate current to approximately 10 mA.
• Grid Voltage for Low Plate Currents:
  • Section One (for $I_b = 20\ \mu\text{A}$): -5.3 V (or -5.5 V for $I_b = 10\ \mu\text{A}$)
  • Section Two (for $I_b = 200\ \mu\text{A}$): -45 V (or -45 V for $I_b = 100\ \mu\text{A}$)

Maximum Ratings and Circuit Design Constraints

The maximum ratings of the 15EA7 are defined under the Design-Maximum Rating System. These ratings are limiting values of operating and environmental conditions and must not be exceeded under the worst probable conditions.

Vertical Deflection Service Ratings (525-Line, 30-Frame System)

Note: Some alternative tables list a maximum DC plate voltage of 330 V for both sections and a plate dissipation of 1.5 W for Section One.

Pulse and Bias Constraints

• Pulse Duration: The peak positive pulse plate voltage rating of 1,500 V for Section Two is an absolute maximum. The pulse duration must not exceed 15% of a single vertical scanning cycle (which corresponds to 2.5 milliseconds in a standard 525-line, 30-frame television system).
• Grid Circuit Resistance Limits:
  • For both Section One and Section Two, the maximum grid circuit resistance is restricted to 1.0 Megohm under fixed-bias conditions and 2.2 Megohms under cathode-bias (self-bias) conditions.
• Excitation Protection: In stages operating with grid-leak bias, an adequate cathode-bias resistor or other protective means must be employed to safeguard the tube against excessive dissipation in the absence of input excitation.

Interelectrode Capacitances

The direct interelectrode capacitances of the 15EA7 are measured approximately without an external shield: