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Voltage Dual Triode Pentode ·Pentode-Triode-Triode

11BT11

Duodecar television tube combining two general-purpose triodes with a sharp-cutoff pentode specifically intended for video amplification, integrating three receiver signal-processing stages in one envelope.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
3
Base
12GS
Socket code
B12C
Base pins
12
Nominal heater
10.7 V / 600 mA

Description

11BT11 — Dissimilar Double Triode and Sharp-Cutoff Pentode Compactron

Overview

The 11BT11 is a multi-unit vacuum tube of the compactron (or duodecar) design, containing three electrically distinct active structures within a single T-9 glass envelope. It integrates a high-mu triode (Section 1), a medium-mu triode (Section 2), and a high-transconductance, sharp-cutoff, frame-grid pentode.

The tube is primarily designed for television receiver applications. The high-performance pentode section is specifically intended for video-amplifier service, while the two dissimilar triode sections are designed for general-purpose applications, such as voltage amplification, oscillation, or sync separation. The 11BT11 features a 12-pin button base and an indirectly heated cathode system with a controlled heater warm-up time.

Construction, Heater, and Pinout

The 11BT11 is housed in a T-9 glass bulb with a 12-pin button base (E12-70 designation) and conforms to the EIA 9-58 outline. It can be operated in any physical position.

Physical Dimensions

  • Maximum Diameter: 1.188 inches
  • Minimum Diameter: 1.062 inches
  • Maximum Overall Length: 2.375 inches
  • Maximum Seated Height: 2.000 inches
  • Minimum Seated Height: 1.750 inches

Heater Characteristics

The tube utilizes coated unipotential cathodes. The heater is designed for series or parallel AC/DC operation with a controlled warm-up characteristic to ensure reliability in series-string television receivers.

ParameterValue
Nominal Heater Voltage (AC or DC)10.7 V
Nominal Heater Current0.6 ± 0.04 A
Average Heater Warm-up Time11 seconds

Heater-Cathode Voltage Ratings

  • 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

Terminal Connections and Basing

The 11BT11 uses the EIA 12GS basing diagram. The pin connections, viewed from the bottom of the base, are as follows:

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

Note on Electrode Independence: While Triode Section 2 and the Pentode section have fully independent cathodes (Pins 4 and 8, respectively), Triode Section 1 shares its cathode connection (Pin 6) with the Pentode's suppressor grid (Grid Number 3) and the tube's internal shield. This common connection must be accounted for in circuit design, particularly when biasing Triode Section 1.

Electrical Characteristics and Class A1 Operation

The three active sections of the 11BT11 exhibit highly distinct electrical properties, reflecting their specialized roles. The pentode section features a frame-grid construction that achieves exceptionally high transconductance (19,000 µmhos) at typical operating points. Triode Section 1 is a high-mu voltage amplifier (μ = 69), whereas Triode Section 2 is a medium-mu unit (μ = 40) with lower plate resistance.

Typical Operating Characteristics

ParameterTriode Section 1Triode Section 2Pentode Section (Low Eb)Pentode Section (Typical)
Plate Voltage200 V200 V35 V150 V
Grid-No. 2 (Screen) Voltage——100 V100 V
Grid-No. 1 (Control) Voltage——0 V—
Cathode-Bias Resistor270 Ω470 Ω—82 Ω
Amplification Factor (μ)6940——
Plate Resistance (Approx.)12,500 Ω7,600 Ω—51,000 Ω
Transconductance (gm)5,500 µmhos5,300 µmhos—19,000 µmhos
Plate Current (Ib)7.1 mA7.2 mA54 mA17.4 mA
Grid-No. 2 Current (Ic2)——13.5 mA3.2 mA
Grid-No. 1 Cutoff Voltage-5.5 V (at Ib = 50 µA)-8 V (at Ib = 100 µA)—-6.6 V (at Ib = 100 µA)

Maximum Ratings and Circuit Values

The maximum ratings are established under the Design-Maximum System. These ratings represent limiting values of operating and environmental conditions that should not be exceeded under the worst probable circumstances.

Design-Maximum Ratings

RatingTriode Section 1Triode Section 2Pentode Section
Plate Voltage330 V330 V165 V
Grid-No. 2 (Screen) Voltage——165 V
Positive DC Grid-No. 1 Voltage0 V0 V0 V
Plate Dissipation1.5 W2.0 W3.5 W
Grid-No. 2 (Screen) Input——1.5 W

Maximum Circuit Values (Grid-No. 1 Circuit Resistance)

Bias TypeTriode Section 1Triode Section 2Pentode Section
Fixed-Bias Operation0.5 MΩ0.5 MΩ0.05 MΩ (50,000 Ω)
Cathode-Bias Operation1.0 MΩ1.0 MΩ0.1 MΩ (100,000 Ω)

Interelectrode and Coupling Capacitances

Because the 11BT11 houses three high-gain stages in close proximity, internal shielding and direct interelectrode capacitances are critical design factors. The following values are measured without an external shield:

Direct Interelectrode Capacitances

  • Triode Section 1:

    • Grid to Plate (1Tg to 1Tp): 1.9 pF
    • Input [1Tg to (1Tk + Pg3 + h + i.s.)]: 2.8 pF
    • Output [1Tp to (1Tk + Pg3 + h + i.s.)]: 2.0 pF

  • Triode Section 2:

    • Grid to Plate (2Tg to 2Tp): 2.6 pF
    • Input [2Tg to (2Tk + 1Tk + Pg3 + h + i.s.)]: 4.6 pF
    • Output [2Tp to (2Tk + 1Tk + Pg3 + h + i.s.)]: 3.6 pF

  • Pentode Section:

    • Grid-No. 1 to Plate (Pg1 to Pp): 0.13 pF
    • Input [Pg1 to (Pk + 1Tk + Pg2 + Pg3 + h + i.s.)]: 13 pF
    • Output [Pp to (Pk + 1Tk + Pg2 + Pg3 + h + i.s.)]: 4.6 pF

Inter-Unit Coupling Capacitances

  • Pentode Plate to Triode Plate (Section 2) (Pp to 2Tp): 0.08 pF maximum
  • Triode Plate (Section 1) to Triode Plate (Section 2) (1Tp to 2Tp): 0.19 pF maximum

Characteristic Curves and Design Interpretation

The published characteristic curves for the 11BT11 illustrate the performance capabilities and biasing requirements of each section:

Pentode Section Curves

  • Average Plate Characteristics: Plotting plate current (Ib) and screen current (Ic2) against plate voltage reveals typical pentode behavior. At a screen voltage (Ec2) of 100 V, the plate current rises extremely sharply at very low plate voltages (below 25 V) and remains highly flat and independent of plate voltage across the rest of the operating range. Increasing the screen voltage to 150 V shifts the curves upward, significantly increasing the available plate current for a given control-grid bias.
  • Average Transfer Characteristics: These curves plot plate and screen currents against Grid-No. 1 voltage. They show a sharp-cutoff characteristic, with plate current approaching zero near -6.6 V when the screen is at 100 V.
  • Transconductance vs. Grid-No. 1 Voltage: The transconductance (gm) curve rises steeply as the control grid bias approaches 0 V, demonstrating the high gain capability of the frame-grid design, which peaks at 19,000 µmhos under typical operating conditions.

Triode Section 1 Curves

  • Average Plate Characteristics: The plate current curves for various grid voltages (from 0 V to -7.0 V) show typical high-mu triode behavior, requiring relatively small negative grid voltages to control plate current.
  • Average Characteristics vs. Plate Current: At a plate voltage (Eb) of 200 V, the amplification factor (μ) remains remarkably constant near 69 across a wide range of plate currents (from 2 mA to 14 mA). Over this same range, the plate resistance (rp) drops from approximately 25,000 Ω to 10,000 Ω, while the transconductance (gm) rises from 2,500 µmhos to over 6,000 µmhos.

Triode Section 2 Curves

  • Average Plate Characteristics: The curves for Triode Section 2 span grid voltages from 0 V to -10 V. The lower slope of these curves compared to Section 1 reflects its lower plate resistance and medium-mu design.
  • Average Characteristics vs. Plate Current: At Eb = 200 V, the amplification factor (μ) is stable near 40. The plate resistance (rp) is significantly lower than that of Section 1, dropping from about 15,000 Ω at low currents to approximately 6,000 Ω at higher currents, while transconductance (gm) rises from 2,500 µmhos to nearly 7,000 µmhos as plate current increases toward 20 mA.

Technical Summary

The 11BT11 is a highly integrated compactron/duodecar multi-unit tube designed to consolidate multiple functions in television receivers. By combining a high-mu triode (μ = 69), a medium-mu triode (μ = 40), and a high-transconductance, sharp-cutoff frame-grid pentode (gm = 19,000 µmhos) into a single T-9 envelope, it reduces chassis space and component count.

Its heater is optimized for series-string operation with a 10.7 V, 0.6 A rating and a controlled 11-second warm-up time. Designers must respect the shared cathode connection on Pin 6 (linking Triode 1's cathode to the pentode's suppressor grid and internal shield) and adhere to the design-maximum ratings, particularly the 165 V limit on the pentode plate and screen grid, to ensure reliable operation in video-amplifier and general-purpose television circuitry.

Socket description

Duodecar 12-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
12GS
Socket code
B12C
Base pins
12
Nominal heater voltage
10.7 V
Nominal heater current
600 mA
Parallel heater voltage
-
Parallel heater current
-
Series capable
No

12GS - Terminal pinout

Electrical assignments shared by every tube using this base designation.

No verified pinout is recorded for this base designation.

Section ratings

3 physical sections, each with unique specifications.

Section 1

Pentode

X-ray radiationInterelectrode capacitances
Plate resistance
51000 Ω
Transconductance
0.019 S
Max plate voltage
165 V
Max screen voltage
165 V
Max plate dissipation
3.5 W
Max screen dissipation
1.5 W

Sharp-cutoff video-amplifier pentode.

Section 2

Triode

X-ray radiationInterelectrode capacitances
Plate resistance
12500 Ω
Transconductance
0.0055 S
Amplification factor
69
Max plate voltage
330 V
Max plate dissipation
1.5 W

Triode Section 1 in source.

Section 3

Triode

X-ray radiationInterelectrode capacitances
Plate resistance
7600 Ω
Transconductance
0.0053 S
Amplification factor
40
Max plate voltage
330 V
Max plate dissipation
2 W

Triode Section 2 in source.

Source-dependent data

Operating conditions by source

Each block preserves the test conditions and published values from one reference. Values from different sources are intentionally kept separate.

Data set 01

1968 General Electric Co

Published operating points and test conditions from this source.

SECTION 1

Pentode

Other

  • Plate Voltage

    35 V

  • Plate Voltage

    -55611 V

  • Plate Voltage

    -55611 V

  • Screen Voltage

    165 V

  • Screen Voltage

    4 V

  • Plate Dissipation

    4 W

  • ScreenDissipation

    4 W

  • Plate Current

    25 mA

  • Plate Current

    -55611 mA

  • Plate Current

    -55611 mA

  • Screen Current

    13.5 mA

  • Transconductance

    19000 uS

  • Transconductance

    5500 uS

  • Transconductance

    6 uS

  • Plate Resistance

    51000 ohm

  • Plate Resistance

    12500 ohm

  • Plate Resistance

    30 ohm

  • Grid Voltage

    50 V

  • Grid Voltage

    100 V

  • Grid Voltage

    -55611 V

  • Grid Voltage

    -55611 V

  • Plate Voltage

    150 V

    AverageCharacteristics

  • Screen Voltage

    100 V

    AverageCharacteristics

Characteristic

  • Plate Current

    17.4 mA

    AverageCharacteristics

  • Screen Current

    3.2 mA

    AverageCharacteristics

SECTION 2

Triode

Other

  • Plate Voltage

    200 V

    AverageCharacteristics

Characteristic

  • Plate Current

    7.1 mA

    AverageCharacteristics

SECTION 3

Triode

Other

  • Plate Voltage

    200 V

    AverageCharacteristics

Characteristic

  • Plate Current

    7.2 mA

    AverageCharacteristics

Data set 02

1975 RCA RC30

Published operating points and test conditions from this source.

SECTION 1

Pentode

Other

  • Plate voltage

    150 V

    ClassA

  • Screen-grid voltage

    100 V

    ClassA

  • Cathode-bias resistor

    82 ohm

    ClassA

  • Plate current

    17.4 mA

    ClassA

  • Screen-grid current

    3.2 mA

    ClassA

SECTION 2

Triode

Other

  • Plate voltage

    200 V

    ClassA

  • Cathode-bias resistor

    270 ohm

    ClassA

  • Plate current

    7.1 mA

    ClassA

SECTION 3

Triode

Other

  • Plate voltage

    35 V

    ClassA

  • Cathode-bias resistor

    470 ohm

    ClassA

  • Plate current

    7.2 mA

    ClassA