11BQ11 — Dissimilar Double Pentode Compactron

The 11BQ11 is a multi-electrode compactron-type vacuum tube containing two dissimilar pentode sections in a single envelope. Section 1 is designed as a remote-cutoff (or semiremote-cutoff) pentode, while Section 2 is a sharp-cutoff pentode. This combination is intended primarily for use in the intermediate-frequency (IF) amplifier stages of television receivers, particularly color television sets.

Mechanical Design, Basing, and Physical Dimensions

The 11BQ11 is constructed in a T-9 glass envelope utilizing a 12-pin button base (E12-70), which requires a standard duodecar 12-contact socket. The tube can be operated in any position.

The physical dimensions of the envelope are standardized under the EIA 9-58 outline:

Terminal Connections and Basing Diagram

The tube utilizes the 12DM basing arrangement. The pin connections, viewed from the bottom of the base, are assigned as follows:

• Pin 1: Heater
• Pin 2: Plate (Section 2)
• Pin 3: Grid Number 2 (Screen Grid) (Section 2)
• Pin 4: Grid Number 3 (Suppressor Grid) (Section 2)
• Pin 5: Grid Number 1 (Control Grid) (Section 2)
• Pin 6: Cathode (Section 2)
• Pin 7: Grid Number 3 (Suppressor Grid) (Section 1) and Internal Shield
• Pin 8: Plate (Section 1)
• Pin 9: Grid Number 2 (Screen Grid) (Section 1)
• Pin 10: Grid Number 1 (Control Grid) (Section 1)
• Pin 11: Cathode (Section 1)
• Pin 12: Heater

In this configuration, Section 1's suppressor grid is internally tied to the internal shield and brought out to Pin 7, whereas Section 2's suppressor grid is brought out independently to Pin 4. Both sections feature coated unipotential cathodes.

Heater Characteristics and Ratings

The heater of the 11BQ11 is designed for series or parallel AC/DC operation. It features controlled warm-up characteristics to ensure reliable operation in series-string receiver designs.

The average heater warm-up time is defined as the time required for the voltage across the heater to reach 80 percent of its nominal value when a voltage equal to 4 times the nominal heater voltage is applied to a circuit consisting of the tube heater in series with a resistance equal to 3 times the nominal heater voltage divided by the nominal heater current.

Heater-Cathode Voltage Limits

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

• Heater Negative with Respect to Cathode:
  • Total DC and Peak: 200 V maximum
• Heater Positive with Respect to Cathode:
  • DC Component: 100 V maximum
  • Total DC and Peak: 200 V maximum

Direct Interelectrode Capacitances

The capacitances of the individual sections are measured with an external shield (EIA 309) connected to the cathode of the section under test.

Section 1 (Remote-Cutoff Pentode)

• Grid No. 1 to Plate: 0.022 pF
• Input (1g1 to [1k + 1g2 + 1g3 + h + i.s.]): 10 pF
• Output (1p to [1k + 1g2 + 1g3 + h + i.s.]): 2.8 pF

Section 2 (Sharp-Cutoff Pentode)

• Grid No. 1 to Plate: 0.024 pF
• Input (2g1 to [2k + 2g2 + 2g3 + 1g3 + h + i.s.]): 11 pF
• Output (2p to [2k + 2g2 + 2g3 + 1g3 + h + i.s.]): 2.8 pF

Inter-Section Coupling Capacitances

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

These low coupling capacitances indicate that despite sharing a single envelope, the two pentode sections are highly isolated from each other, minimizing unwanted crosstalk in high-frequency applications.

Maximum Ratings (Design-Maximum Values)

The maximum ratings are established under the Design-Maximum Rating System. These are limiting values of operating and environmental conditions that should not be exceeded under the worst probable conditions in a bogey tube. Both Section 1 and Section 2 share identical maximum ratings.

The screen-grid voltage and dissipation for voltages between 165 V and 330 V are restricted by the Screen Rating Chart. Up to 165 V, the maximum screen dissipation is flat at 0.65 W. Above 165 V, the permissible dissipation decreases along a curve, dropping to 0 W at 330 V, to protect the screen grid from thermal overload.

Electrical Characteristics and Typical Class A1 Operation

Typical operating characteristics for both sections are evaluated at a plate supply voltage of 125 V with the suppressor grid connected to the cathode at the socket.

Analysis of Section Characteristics

• Section 1 (Remote-Cutoff Pentode): Under typical operating conditions, Section 1 exhibits a transconductance of 10,500 Ͱmhos. Its remote-cutoff characteristic is demonstrated by the fact that a relatively large negative grid bias of approximately -15 V is required to reduce the transconductance to 50 Ͱmhos. This allows the stage to handle large signal swings and interface effectively with automatic gain control (AGC) circuitry without causing clipping or cross-modulation.
• Section 2 (Sharp-Cutoff Pentode): Section 2 provides a higher transconductance of 13,000 Ͱmhos under the same typical operating conditions. It features a sharp-cutoff characteristic, with plate current falling to 20 ͰA at a grid bias of approximately -3 V. This sharp transition makes it highly suitable for high-gain, stable amplification where AGC control is not required or is restricted to a narrow range.

Related Designations and Family Comparison

The 11BQ11 is part of a family of three identical compactrons that differ only in their heater ratings:

• 8BQ11: Designed with an 8.4 V, 0.6 A heater.
• 11BQ11: Designed with an 11.2 V, 0.45 A heater.
• 16BQ11: Designed with a 16 V, 0.315 A heater.

All three tubes share the same T-9 glass envelope, 12DM basing diagram, maximum ratings, and electrical characteristics. They must not be confused with other dissimilar double pentodes such as the 8BM11, which has lower maximum ratings (160 V plate voltage, 2.2 W plate dissipation) and lower transconductance values (8,800 Ͱmhos for Section 1 and 8,500 Ͱmhos for Section 2).

Technical Summary

The 11BQ11 is a 12-pin compactron dissimilar double pentode featuring a remote-cutoff pentode (Section 1) and a sharp-cutoff pentode (Section 2) in a single T-9 glass envelope. Operating from an 11.2 V, 0.45 A heater with controlled warm-up characteristics, it is optimized for series-string television receiver designs.

With a maximum plate voltage rating of 330 V and plate dissipation of 3.1 W per section, the tube provides high-performance intermediate-frequency amplification. Section 1 delivers a transconductance of 10,500 Ͱmhos with a remote-cutoff bias of -15 V, while Section 2 delivers 13,000 Ͱmhos with a sharp-cutoff bias of -3 V. Its low inter-section coupling capacitances (such as a plate-to-plate capacitance of 0.015 pF) ensure excellent isolation between the two active stages.