13GB5 — Beam Power Pentode

The 13GB5 (also designated as 13GB5/XL500) is a Magnoval-type beam power pentode designed primarily for use as a horizontal-deflection amplifier in television receivers. It is engineered to deliver high peak plate currents at low plate voltages, which is a critical requirement for efficient horizontal-output stages in television scanning systems.

Overview

The 13GB5 is a specialized power tube designed for series-string heater applications. It is electrically identical to the 6GB5/EL500 except for its heater ratings. The tube belongs to a family of identical beam power pentodes that includes the 18GB5/LL500, 27GB5/PL500, and 28GB5, each tailored for different heater supply configurations.

The device features a Magnoval T-9 glass envelope and requires a neonoval 9-contact socket. To handle the high-voltage pulses generated during the horizontal flyback interval, the plate connection is brought out to a top cap, isolating it from the other electrodes at the base.

Construction, Physical Dimensions, and Pinout

The 13GB5 is constructed with a Magnoval T-9 glass envelope and a Button 9-Pin (E9-23) base. The physical dimensions of the tube are as follows:

• Maximum Diameter: 1.188 inches
• Maximum Seated Height: 3.750 inches
• Maximum Overall Height: 4.125 inches

Pinout and Basing (9NH)

The tube utilizes the 9NH basing arrangement. The pin connections, viewed from the bottom of the base, are:

The duplicate connections for Grid No. 1 (Pins 1 and 2), Grid No. 2 (Pins 6 and 7), and Cathode/Grid No. 3 (Pins 3 and 8) are provided to reduce lead inductance and simplify circuit layout.

Heater Characteristics and Ratings

The heater of the 13GB5 is designed for series-string operation in television receivers.

• Heater Voltage (AC or DC): 13.3 V (at 0.600 A) or 13 V (depending on the specific rating standard)
• Heater Current: 0.600 A (with a tolerance of ±0.040 A)

Heater Power Calculation

Using the nominal ratings, the heater power consumption can be calculated as: $\text{Heater Power} = 13.3\text{ V} \times 0.600\text{ A} = 7.98\text{ W}$ Or, using the alternative 13 V nominal rating: $\text{Heater Power} = 13.0\text{ V} \times 0.600\text{ A} = 7.80\text{ W}$

Heater-Cathode Voltage Limits

To prevent insulation breakdown between the heater and the cathode, the following maximum voltage limits must be respected:

• Heater Negative with Respect to Cathode:
  • DC: 125 V maximum
  • Total DC and Peak: 250 V maximum
• Heater Positive with Respect to Cathode:
  • DC: 125 V maximum
  • Total DC and Peak: 250 V maximum

Electrical Ratings (Design-Maximum System)

The maximum ratings for the 13GB5 are specified under the Design-Maximum Rating System for operation in a 525-line, 30-frame television system:

Note on Peak Positive-Pulse Plate Voltage: The pulse duration must not exceed 15% of a horizontal scanning cycle, which corresponds to a maximum duration of 10 microseconds.

Maximum Circuit Values

• Grid-No. 1 Circuit Resistance (Without grid current): 0.5 MΩ
• Grid-No. 1 Circuit Resistance (With grid current, horizontal-output service only): 2.2 MΩ

Typical Instantaneous Characteristics (Knee Values)

The 13GB5 is designed to exhibit a very sharp "knee" in its plate characteristic curves, allowing high plate current at low plate voltages. The typical instantaneous characteristics (measured with a recurrent waveform to avoid exceeding maximum ratings) are:

• Plate Voltage ($E_b$): 75 V
• Grid-No. 2 Voltage ($E_{c2}$): 200 V
• Grid-No. 1 Voltage ($E_{[c1](/tubes/C1)}$): -10 V
• Plate Current ($I_b$): 440 mA
• Grid-No. 2 Current ($I_{c2}$): 37 mA

These values demonstrate the tube's ability to conduct heavily (440 mA) even when the plate voltage drops to 75 V, which is essential for minimizing plate dissipation and maximizing efficiency during the end-of-scan period.

Horizontal-Deflection Amplifier Operation

The 13GB5 can be operated in either stabilized or non-stabilized horizontal-deflection circuits. The following tables outline typical operating parameters at various supply voltages.

Stabilized Circuit Operation

In these typical operating conditions, a minimum value of screen-grid resistor ($R_{[g2](/tubes/G2)}$) is required to prevent excessive screen-grid dissipation during the heater warm-up period.

Non-Stabilized Circuits (Drive Below the Knee)

For circuits where the tube is driven below the knee of the plate characteristic:

Circuit Design Considerations

• Cut-off Voltage: The minimum required control-grid voltage for complete cut-off during the flyback interval is -120 V.
• Excitation Protection: A bias resistor or other protective means must be incorporated in the circuit to protect the tube from excessive current in the event that excitation drive is lost.
• Line Voltage Variations: The typical operating values are specified for nominal line voltage. If the line voltage drops by up to 10% below nominal, the tube is designed to continue operating above the knee.
• Peak Plate Current Limits: To account for tube-to-tube variations (spread), performance deterioration over the tube's operating life, and a 10% reduction in line voltage, the peak plate current should not exceed the specified values under nominal line voltage conditions.

Related Designations and Comparisons

The 13GB5 is part of a family of identical beam power pentodes that share the same internal structure, physical dimensions, and electrical ratings, differing only in their heater requirements:

• 6GB5/EL500: Designed for standard parallel heater circuits, requiring 6.3 V at 1.38 A (1380 mA).
• 13GB5/XL500: Designed for 0.6 A series-string circuits, requiring 13.3 V (or 13 V) at 0.6 A.
• 18GB5/LL500: Designed for 0.45 A series-string circuits, requiring 18 V at 0.45 A.
• 27GB5/PL500: Designed for 0.3 A series-string circuits, requiring 27 V (or 28 V) at 0.3 A.
• 28GB5: Designed for 0.3 A series-string circuits, requiring 28 V at 0.3 A (300 mA).

These tubes are highly specialized for horizontal-deflection service and require a Magnoval/neonoval 9-contact socket.

Technical Summary

The 13GB5 (or 13GB5/XL500) is a high-performance, Magnoval-type beam power pentode optimized for horizontal-deflection amplifier service in television receivers. It features a T-9 glass envelope, a Button 9-Pin (E9-23) base, and a C1-2 top cap for the plate connection. Operating with a 13.3 V / 0.6 A heater, it is tailored for series-string heater chains. The tube is capable of handling a peak positive-pulse plate voltage of up to 7700 V and a plate dissipation of 17 W. Its unique design allows it to deliver high peak plate currents (up to 440 mA instantaneously at a plate voltage of only 75 V), ensuring highly efficient operation in horizontal-output stages.