19BG6G — Beam Power Amplifier

The 19BG6G (also written as 19BG6-G) is a glass-envelope beam power amplifier and beam pentode designed primarily for use in television receiver horizontal deflection circuits and line time base output stages. It represents a mechanical redesign of the classic 6L6G structure, modified with a top-cap anode connection and enhanced insulation to withstand the high peak positive plate voltages encountered in television flyback systems.

Overview and Applications

In AC/DC television receivers, the 19BG6G functions as a line time base output valve. It can also operate in conjunction with a rectifier (such as the Brimar R12) to generate Extra High Tension (E.H.T.) power from line flyback pulses. For further characteristic curves and detailed information, reference is frequently made to the electrically similar 6BG6G tube type.

Construction, Physical Dimensions, and Mounting

The 19BG6G features a coated unipotential cathode and is housed in an ST-16 glass bulb (outline drawing 16-5) with a small top cap for the anode (plate) connection. This top-cap configuration isolates the high-voltage anode from the base pins, providing the necessary insulation to prevent arcing during high-voltage pulses.

Physical Dimensions

• Maximum Diameter/Width: 2-1/16 inches
• Maximum Overall Height: 5-5/8 to 5-11/16 inches
• Maximum Seated Height: 5-1/8 inches

Mounting Position

The tube can be mounted in either a vertical (base up or down) or horizontal position. When mounted horizontally, the plane of pins 2 and 7 must be oriented vertically.

Heater and Base Connections

The heater of the 19BG6G is designed for series or parallel AC/DC operation, requiring a nominal voltage of 18.9 to 19 volts and a current of 0.3 amperes (300 mA).

Pinout Configurations

The 19BG6G utilizes an octal base (specifically a medium shell 6-pin octal base with a 5BT basing designation). The pin connections vary slightly across different manufacturer specifications:

• Configuration A:

  • Pin 1: No Connection (NC)
  • Pin 2: Heater (h)
  • Pin 3: Cathode, Beam Plates (k, bp)
  • Pin 4: No Pin (NP)
  • Pin 5: Control Grid (g1)
  • Pin 6: No Pin (NP)
  • Pin 7: Heater (h)
  • Pin 8: Screen Grid (g2)
  • Top Cap: Anode (a)

• Configuration B:

  • Pins 2 & 7: Heater (h)
  • Pin 4: Screen Grid (g2)
  • Pin 5: Control Grid (g1)
  • Pin 8: Cathode & Grid No. 3 (k, g3)
  • Top Cap: Plate (p)

• Configuration C:

  • Pin 1: No Connection (NC)
  • Pin 2: Heater (H)
  • Pin 3: Grid No. 2 (G2)
  • Pin 7: Heater (H)
  • Pin 8: Cathode & Grid No. 3 (K, G3)
  • Top Cap: Plate (P)

These variations reflect different historical standards and base configurations (such as the 5BT designation).

Electrical Characteristics and Typical Operation

The 19BG6G is characterized by high transconductance and a low knee voltage, making it highly efficient in deflection amplifier service.

Direct Interelectrode Capacitances (Without External Shield)

• Grid No. 1 to Plate (g1 to p): 0.34 pF to 0.65 pF (maximum)
• Input (g1 to h + k + g3 + g2): 11 pF to 12 pF
• Output (p to h + k + g3 + g2): 6.5 pF

Typical Operating Conditions (Class A / Static)

Under static conditions, the tube exhibits the following characteristics:

Typical Operation in a Horizontal Deflection Circuit

When operating in a practical television horizontal deflection circuit, typical parameters are as follows:

• Heater Voltage: 18.9 V
• Heater Current: 300 mA
• Plate & Grid No. 2 Supply Voltage: 400 V
• Peak Positive Surge Plate Voltage (Approx.): 4,000 V
• Peak Negative Surge Grid No. 1 Voltage (Approx.): -100 V
• Plate Current: 70 mA
• Grid No. 2 Current: 6 mA
• Grid No. 1 Current: 25 µA

Maximum Ratings

The maximum ratings of the 19BG6G must be strictly observed to prevent premature failure, particularly in horizontal deflection systems where high-voltage flyback pulses are present. The ratings are interpreted according to the RMA Standard M8-210.

* Note on Peak Positive Surge Plate Voltage: The duty cycle of the voltage pulse must not exceed 15% of one scanning cycle, and the pulse duration must be limited to 10 microseconds.

Qualitative Curve Observations

Analysis of the 19BG6G characteristic curves reveals several key performance traits:

• Plate Characteristics ($E_f = 18.9\text{ V}, E_{c2} = 250\text{ V}$): The "knee" of the plate current curves occurs sharply between 50 V and 70 V plate voltage across a wide range of control grid ($E_{[c1](/tubes/C1)}$) voltages from +10 V to -30 V. This sharp knee allows for maximum current swing and high efficiency in deflection circuits.
• Plate Characteristics ($E_f = 18.9\text{ V}, E_{[c1](/tubes/C1)} = 0\text{ V}$): The plate current curves exhibit well-defined saturation plateaus for screen voltages ($E_{c2}$) ranging from 50 V to 350 V.
• Screen Current Characteristics ($E_f = 18.9\text{ V}, E_{[c1](/tubes/C1)} = 0\text{ V}$): Screen current ($I_{c2}$) remains low and flat at higher plate voltages, which minimizes screen dissipation during normal conduction. However, as the plate voltage drops below approximately 50 V (below the knee), the screen current rises sharply.

Technical Summary

The 19BG6G is an octal-based, indirectly heated beam power pentode designed specifically for high-stress horizontal deflection amplifier and line time base output service in AC/DC television receivers. Featuring an 18.9 V / 0.3 A heater, a rugged ST-16 glass envelope, and a top-cap anode connection, it is mechanically optimized to withstand peak positive plate surges of up to 6,600 V. With a plate dissipation rating of 20 W, a transconductance of 6,000 µmhos, and a sharp knee characteristic, the 19BG6G provides reliable and efficient performance in television scanning systems.