12GE5 — Beam Power Compactron

An indirectly heated beam power pentode in a compactron envelope, designed primarily for horizontal-deflection amplifier service in television receivers.

Overview

The 12GE5 is a high-performance beam power pentode designed in the compactron configuration. It is primarily intended for service as a horizontal-deflection amplifier in television receivers operating under 525-line, 30-frame scanning systems.

The 12GE5 features a coated unipotential cathode and is electrically identical to the 6GE5 and 17GE5 vacuum tubes, with the sole exception of its heater characteristics and warm-up time. It is housed in a T-12 glass envelope and utilizes a standard 12-pin duodecar base, which requires a duodecar 12-contact socket.

Physical Construction and Basing

The 12GE5 is constructed using the compactron T-12 design, which provides a compact and mechanically robust structure. The tube can be mounted in any position.

The physical dimensions of the envelope are as follows:

• Maximum Diameter: 1.563 inches
• Maximum Seated Height: 2.500 inches
• Maximum Overall Height: 2.875 inches

Pinout and Basing Diagram

The tube uses the 12BJ JEDEC basing diagram with a 12-pin button base (E12-74 outline). The pin connections, viewed from the bottom of the tube, are:

Pins designated as "Internal Connection" (IC) should not be used for circuit connections.

Heater Characteristics and Ratings

The 12GE5 is designed for series-string heater circuits or parallel operation, with controlled warm-up characteristics to minimize voltage surges in series-connected receiver designs.

Heater Warm-up Time Definition

The average heater warm-up time of 11 seconds is defined under specific test conditions. It represents the time required for the voltage across the heater to reach 80% of its rated value when four times the rated heater voltage is applied to a circuit consisting of the tube heater in series with an external resistance. This series resistance must equal three times the nominal heater operating resistance at its normal operating temperature.

Heater-Cathode Voltage Limits

To prevent insulation breakdown and hum injection, the voltage between the heater and cathode must be kept within the following design-maximum limits:

• Heater Positive with Respect to Cathode:
  • DC Component: 100 V maximum
  • Total DC and Peak: 200 V maximum
• Heater Negative with Respect to Cathode:
  • Total DC and Peak: 200 V maximum
• General Limits: Peak value of ±200 V maximum, with an average value of 100 V maximum.

Direct Interelectrode Capacitances

The direct interelectrode capacitances of the 12GE5, measured without an external shield, are approximately:

• Grid No. 1 to Plate (G1 to P): 0.34 pF
• Input (G1 to H + K + G2 + B.P.): 16 pF
• Output (P to H + K + G2 + B.P.): 7.0 pF

(Note: B.P. represents the beam plates / Grid No. 3).

Typical Operating Characteristics (Class A1)

The 12GE5 can be operated as either a pentode or a triode (with Grid No. 2 tied to the plate). The typical characteristics at standard operating points are detailed below:

Pentode Connection

Under typical Class A1 conditions, the tube exhibits the following characteristics:

At an elevated plate voltage of 5000 V (with Grid No. 2 at 150 V), the control-grid voltage required to reduce the plate current to approximately 1.0 mA is -100 V.

Triode Connection

When Grid No. 2 is connected directly to the plate, the 12GE5 operates as a triode with the following characteristics:

• Plate Voltage: 150 V
• Grid No. 2 Voltage: 150 V
• Grid No. 1 Voltage: -22.5 V
• Amplification Factor ($\mu$): 4.4

Horizontal-Deflection Amplifier Ratings

Because the 12GE5 is designed for the demanding pulse-service environment of television horizontal-deflection circuits, its ratings are established under the Design-Maximum System.

Operating Precautions and Pulse Limits

• Pulse Duration: The peak positive-pulse plate voltage rating of 6500 V is an absolute maximum value. It is restricted to a maximum pulse duration of 15% of a horizontal scanning cycle, which corresponds to 10 microseconds in a standard 525-line, 30-frame television system.
• Tube Protection: In stages operating with grid-leak bias, an adequate cathode-bias resistor or other protective means must be incorporated in the circuit design. This protects the tube from excessive current and potential damage in the event that excitation (drive signal) is lost.

Related Designations

The 12GE5 is part of a family of identical-structure beam power tubes designed for different heater supply systems:

• 6GE5: Designed for standard parallel heater operation with a 6.3 V, 1.2 A heater.
• 17GE5: Designed for series-string heater operation with a 15.8 to 16.8 V, 0.45 A heater.

These three tubes share identical physical dimensions, basing configurations, and electrical ratings, differing only in their heater requirements and warm-up times.

Technical Summary

The 12GE5 is a 12-pin compactron beam power pentode designed specifically for horizontal-deflection amplifier service in television receivers. It operates with a 12.5 to 12.6 V, 0.6 A heater featuring a controlled 11-second warm-up time for series-string applications.

The tube is capable of handling high peak positive-pulse plate voltages up to 6500 V (with a 15% duty cycle limit) and has a maximum plate dissipation rating of 17.5 W. In typical Class A1 pentode operation, it provides a transconductance of 6,600 to 7,300 μmhos and a plate resistance of 18,000 to 20,000 Ω. The 12GE5 offers a robust, high-voltage switching capability in a compact T-12 glass envelope, making it a highly specialized component for television sweep circuits.