16BQ11 — Semiremote-Cutoff Dual Pentode

The 16BQ11 is a duodecar-type multi-unit vacuum tube containing two independent pentodes in a single envelope. It is designed primarily for use as an intermediate-frequency (IF) amplifier in television receivers. The tube features a semiremote-cutoff pentode (Unit No. 1) and a sharp-cutoff pentode (Unit No. 2), providing circuit designers with two distinct characteristics in a single compact device.

Overview and Family Relationship

The 16BQ11 belongs to a family of dual pentodes that includes the 8BQ11 and 11BQ11. These three types are electrically identical in their pentode structures, maximum ratings, and typical operating characteristics, differing only in their heater configurations. The 16BQ11 is specifically designed with a 16 V heater for series-string heater arrangements in television receivers.

Construction, Heater, and Pinout

The 16BQ11 is constructed in a duodecar glass envelope requiring a standard 12-contact socket. The internal structure features two separate pentode units with independent cathode connections, sharing a common heater. An internal shield is incorporated to minimize capacitive coupling between the two units.

Heater Characteristics

The heater is designed for AC or DC operation. The nominal heater power can be calculated from the rated voltage and current:

$\text{Heater Power} = 16\text{ V} \times 0.315\text{ A} = 5.04\text{ W}$

Pin Connection (12DM Base)

The 16BQ11 utilizes the 12DM basing arrangement, with the following pin assignments viewed from the bottom of the tube:

• Pin 1: Grid No. 1, Unit No. 1 (G1P1)
• Pin 2: Grid No. 2, Unit No. 2 (G2P2)
• Pin 3: Plate, Unit No. 2 (PP2)
• Pin 4: Grid No. 3, Unit No. 2 (G3P2)
• Pin 5: Cathode, Unit No. 2 (KP2)
• Pin 6: Grid No. 1, Unit No. 2 (G1P2)
• Pin 7: Grid No. 3, Unit No. 1, and Internal Shield (G3P1, IS)
• Pin 8: Plate, Unit No. 1 (PP1)
• Pin 9: Grid No. 2, Unit No. 1 (G2P1)
• Pin 10: Cathode, Unit No. 1 (KP1)
• Pin 11: Heater (H)
• Pin 12: Heater (H)

Interelectrode Capacitances

To ensure stable high-frequency operation, the 16BQ11 is designed with low direct interelectrode capacitances. The internal shield is connected to Pin 7 along with Grid No. 3 of Unit No. 1.

Unit Capacitances

Inter-Unit Capacitances

The capacitive isolation between the two pentode sections is characterized by the following extremely low values:

• Plate of Unit No. 1 to Plate of Unit No. 2: 0.015 pF
• Grid No. 1 of Unit No. 1 to Plate of Unit No. 2: 0.002 pF
• Grid No. 1 of Unit No. 2 to Plate of Unit No. 1: 0.008 pF
• Grid No. 1 of Unit No. 1 to Grid No. 1 of Unit No. 2: 0.002 pF

Maximum Ratings (Design-Maximum Values)

The maximum ratings define the operating envelopes for Class A1 amplifier service. These ratings are identical for both pentode units:

• Plate Voltage: 330 V
• Grid-No. 3 (Suppressor-Grid) Voltage: 0 V
• Grid-No. 2 (Screen-Grid) Supply Voltage: 330 V
• Grid-No. 2 Voltage: Subject to rating curves for voltages between 165 V and 330 V
• Grid-No. 1 (Control-Grid) Voltage, Positive-bias value: 0 V
• Plate Dissipation: 3.1 W
• Grid-No. 2 Input:
  • For Grid-No. 2 voltages up to 165 V: 0.65 W
  • For Grid-No. 2 voltages between 165 V and 330 V: Subject to rating curves

Electrical Characteristics and Class A1 Operation

At the typical operating point, both units are operated with a plate supply of 125 V and a screen-grid voltage of 125 V. Grid No. 3 is connected directly to the cathode at the socket.

Cutoff Characteristics

The primary distinction between the two units lies in their control-grid cutoff characteristics:

• Unit No. 1 (Semiremote-Cutoff): Requires an approximate Grid-No. 1 voltage of -15 V to reduce the transconductance to 50 \mu$mhos. This gradual cutoff characteristic is ideal for stages requiring automatic gain control (AGC) without introducing severe distortion.
• Unit No. 2 (Sharp-Cutoff): Requires an approximate Grid-No. 1 voltage of -3 V to reduce the plate current to 20 \mu$A. This sharp cutoff characteristic is optimized for high-gain, stable amplification where AGC is not applied.

Maximum Circuit Values

The maximum allowable control-grid circuit resistance for cathode-bias operation is:

• Unit No. 1: 1.0 M\Omega$
• Unit No. 2: 0.25 M\Omega$

Technical Summary

The 16BQ11 is a high-performance duodecar dual pentode designed for television IF amplifier applications. By combining a semiremote-cutoff pentode (Unit No. 1, $g_m = 10,500\ \mu\text{mhos}$) and a sharp-cutoff pentode (Unit No. 2, $g_m = 13,000\ \mu\text{mhos}$) in a single envelope, it provides a highly integrated solution for multi-stage IF strips. Operating with a 16 V, 0.315 A heater, the tube features excellent inter-unit isolation (plate-to-plate capacitance of only 0.015 pF) and robust design-maximum ratings, including a maximum plate voltage of 330 V and plate dissipation of 3.1 W per unit.