11E16 — High-Frequency Double Tetrode

The 11E16 is an indirectly heated, internally neutralized high-frequency (H.F.) double tetrode designed for use as a push-pull amplifier or frequency trebler at frequencies up to 600 Mc/s. Manufactured under the Ediswan brand by Associated Electrical Industries (AEI) Limited, this valve features a centre-tapped heater and is optimized for high-frequency efficiency, compact physical design, and versatile power amplification.

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Mechanical Construction, Base, and Pinout

The 11E16 is constructed with a compact glass envelope featuring two top-cap anode connections and a specialized seven-pin base. The internal structure is designed to minimize lead inductance and interelectrode capacitance, which is critical for stable operation at very high frequencies.

Physical Dimensions and Weight

• Maximum Overall Length: 85 mm
• Maximum Seated Height: 73 mm
• Maximum Diameter: 47 mm
• Approximate Net Weight: 2 oz (approx. 56.7 g)
• Anode Caps: Two top caps, wire type, 2 mm diameter

Mounting Positions

The mounting requirements depend on the operating environment:

• Mobile Operation: Vertical (base up or down).
• Fixed Station Operation: Vertical (base up or down).
• Horizontal Operation: Permitted only if the anode pins are aligned in a horizontal plane.

Base and Connections

The tube uses a B7A base with an index boss. The pinout configuration, viewed from the free end of the pins, is detailed below:

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Heater Characteristics

The 11E16 features a centre-tapped heater, allowing it to be operated from either a 12.6 V or a 6.3 V power supply. This flexibility makes it suitable for both mobile and fixed-station equipment.

• Series Connection (12.6 V): The heater supply is connected across Pin 1 and Pin 7, leaving Pin 5 (centre tap) unconnected.
  • Heater Voltage ($V_h$): 12.6 V
  • Heater Current ($I_h$): 0.65 A
• Parallel Connection (6.3 V): Pins 1 and 7 are connected together to one side of the supply, and Pin 5 is connected to the other side.
  • Heater Voltage ($V_h$): 6.3 V
  • Heater Current ($I_h$): 1.3 A
• Calculated Heater Power:
  • Series configuration: $12.6\text{ V} \times 0.65\text{ A} = 8.19\text{ W}$
  • Parallel configuration: $6.3\text{ V} \times 1.3\text{ A} = 8.19\text{ W}$

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Electrical Characteristics and Capacitances

The 11E16 is characterized by high transconductance and low internal feedback, aided by internal neutralization. The typical electrical characteristics for each tetrode section, measured under static Class A conditions, are as follows:

Typical Characteristics (Per Section)

Measured at $V_a = 300\text{ V}$, $V_{[g2](/tubes/G2)} = 250\text{ V}$, and $I_a = 20\text{ mA}$:

• Mutual Conductance ($g_m$): 3.0 mA/V
• Inner Amplification Factor ($\mu_{g1-g2}$): 8.0

Inter-electrode Capacitances

The internal neutralization of the 11E16 is specifically designed to facilitate stable push-pull operation without external neutralizing circuits.

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Absolute Maximum Ratings

All limiting values for the 11E16 are specified according to the Absolute rating system, not the Design Centre system. Under no circumstances should these limits be exceeded. The maximum ratings vary depending on the class of service.

Operating Mode Comparison Table

† Value applies to each individual section.

Frequency-Dependent Anode Voltage Derating

At very high frequencies, dielectric losses and transit-time effects require a reduction in the maximum allowable anode voltage. The 11E16's maximum anode voltage ($V_{a(max)}$) is derated based on the operating frequency and cooling method:

1. Class "C" RF Push-Pull (CW / FM)

• Natural Cooling:
  • Up to 150 Mc/s: $V_{a(max)} = 600\text{ V}$
  • At 600 Mc/s: $V_{a(max)} = 250\text{ V}$
• Forced Air Cooling:
  • Up to 300 Mc/s: $V_{a(max)} = 600\text{ V}$
  • At 600 Mc/s: $V_{a(max)} = 400\text{ V}$

2. Class "C" RF Modulated (Anode & Screen)

• Natural Cooling:
  • Up to 150 Mc/s: $V_{a(max)} = 600\text{ V}$
  • At 600 Mc/s: $V_{a(max)} = 250\text{ V}$
• Forced Air Cooling:
  • Up to 250 Mc/s: $V_{a(max)} = 600\text{ V}$
  • At 600 Mc/s: $V_{a(max)} = 440\text{ V}$

Temperature Limits

To ensure reliable operation and prevent premature envelope failure, the following absolute temperature limits must be observed:

• Maximum Permissible Temperature of the hottest part of the bulb: 200 °C
• Maximum Permissible Temperature of the base pins: 180 °C

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Technical Summary

The 11E16 is a highly specialized, internally neutralized high-frequency double tetrode designed for push-pull RF power amplification and frequency multiplication up to 600 Mc/s. Featuring a flexible 6.3 V / 12.6 V centre-tapped heater, a B7A base, and dual top-cap anodes, it provides a compact and efficient solution for transmitter output and driver stages.

With an anode dissipation rating of up to 10 W per section (20 W total combined) and internal neutralization that simplifies circuit design by eliminating external feedback loops, the 11E16 is well-suited for Class C telegraphy, FM telephony, frequency trebling, and Class B audio modulation. Designers must carefully observe the absolute maximum ratings, particularly the frequency-dependent anode voltage derating and the strict bulb and pin temperature limits, to ensure optimal performance and longevity.