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Voltage Dual Triode Pentode ·Pentode-Triode-Triode

15BD11

Three-section Compactron combining high-mu and medium-mu triodes with a sharp-cutoff pentode for television and related signal-amplifier service.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 3
Base: 12DP
Socket code: B12C
Base pins: 12
Nominal heater: 14.7 V / 450 mA

Description

15BD11 — Dual Triode and Sharp-Cutoff Pentode

The 15BD11 is a multi-unit vacuum tube of the Compactron (Duodecar) design, containing three independent active sections within a single T-9 glass envelope. It is specifically engineered for television receiver applications, combining a high-mu triode, a medium-mu triode, and a high-transconductance sharp-cutoff pentode. This combination allows a single envelope to perform multiple distinct roles in a receiver circuit, such as general-purpose voltage amplification, sync separation, and video amplification.

The 15BD11 is designed for series-string heater applications and is identical to the 6BD11 except for its heater ratings and warm-up characteristics.

Construction, Physical Dimensions, and Base

The 15BD11 features a Compactron T-9 construction with a glass envelope and a button 12-pin base (designation E12-70). This configuration requires a standard duodecar 12-contact socket. The physical dimensions of the tube are as follows:

Physical Parameter	Value
Maximum Diameter	1.188 inches
Maximum Seated Height	2.000 inches
Maximum Overall Height	2.375 inches
Outline Designation	9-58
Basing Diagram	12DP

Pin Connections

The 12DP basing arrangement provides independent connections for the three internal sections, with some shared internal shielding. The pin assignments, viewed from the bottom of the base, are:

Pin Number	Connection
Pin 1	Cathode (Triode Unit No. 1)
Pin 2	Plate (Triode Unit No. 2)
Pin 3	Grid (Triode Unit No. 2)
Pin 4	Plate (Pentode Unit)
Pin 5	Heater
Pin 6	Grid (Triode Unit No. 1)
Pin 7	Cathode (Triode Unit No. 2) / Internal Shield
Pin 8	Plate (Triode Unit No. 1)
Pin 9	Cathode (Pentode Unit) / Grid No. 3 / Internal Shield
Pin 10	Grid No. 2 (Screen Grid, Pentode Unit)
Pin 11	Grid No. 1 (Control Grid, Pentode Unit)
Pin 12	Heater

Heater Characteristics and Ratings

The heater of the 15BD11 is designed for series-string operation with a controlled warm-up time to minimize voltage surges in television receiver heater chains.

Heater Parameter	Value
Heater Voltage (AC or DC)	14.7 V
Heater Current	0.450 ± 0.030 A
Average Warm-up Time	11 seconds

Heater-Cathode Voltage Ratings

To maintain insulation integrity between the heater and the separate cathodes of the three units, the following maximum voltage limits must be observed:

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

Electrical Characteristics and Typical Operating Points

The three sections of the 15BD11 operate independently, each optimized for its designated function.

Triode Unit No. 1 (High-Mu Triode)

This section is intended for general-purpose voltage amplification. At a typical operating point, it exhibits a high amplification factor and moderate plate resistance:

Plate Supply Voltage: 200 V
Grid-No. 1 Voltage: -2.0 V
Amplification Factor (\mu): 68
Plate Resistance (Approx.): 12,400 \Omega
Transconductance (g_m): 5,500 \mu mhos
Plate Current: 7.0 mA
Grid-No. 1 Voltage for I_b = 100 \mu A (Approx.): -5.5 V

Triode Unit No. 2 (Medium-Mu Triode)

This section is optimized for sync-separator circuits, featuring a lower amplification factor and lower plate resistance:

Plate Supply Voltage: 200 V
Cathode-Bias Resistor: 220 \Omega
Amplification Factor (\mu): 41
Plate Resistance (Approx.): 9,400 \Omega
Transconductance (g_m): 4,400 \mu mhos
Plate Current: 9.2 mA
Grid-No. 1 Voltage for I_b = 100 \mu A (Approx.): -6.5 V

Pentode Unit (Sharp-Cutoff Pentode)

The pentode section is designed for video amplifier service, offering high transconductance. It can be operated under two typical conditions:

Parameter	Low-Voltage Condition	Standard Condition
Plate Voltage	35 V	135 V
Grid-No. 2 (Screen) Voltage	135 V	135 V
Grid-No. 1 (Control Grid) Voltage	0 V	—
Cathode-Bias Resistor	—	100 \Omega
Plate Resistance (Approx.)	—	45,000 \Omega
Transconductance (g_m)	—	10,400 \mu mhos
Plate Current	34 mA	17 mA
Grid-No. 2 Current	13 mA	4 mA
Grid-No. 1 Voltage for I_b = 100 \mu A (Approx.)	—	-6 V

Maximum Ratings (Design-Maximum System)

The maximum ratings define the operating limits to ensure reliable performance and prevent premature tube failure.

Rating Parameter	Triode Unit No. 1	Triode Unit No. 2	Pentode Unit
Plate Voltage	330 V max	330 V max	330 V max
Grid-No. 2 Supply Voltage	—	—	330 V max
Grid-No. 2 Voltage	—	—	See Rating Chart
Positive DC Grid-No. 1 Voltage	0 V max	0 V max	0 V max
Plate Dissipation	1.5 W max	2.0 W max	4.0 W max
Grid-No. 2 Input (up to 165 V)	—	—	1.1 W max
Grid-No. 2 Input (166 to 330 V)	—	—	See Rating Chart

Note: For the related variant 15BD11A, the maximum screen (Grid-No. 2) dissipation rating is increased to 1.5 Watts.

Maximum Circuit Values

The maximum allowable grid-circuit resistance depends on the biasing method used:

Triode Unit No. 1:
- Fixed Bias: 0.5 M\Omega max
- Cathode Bias: 1.0 M\Omega max
Triode Unit No. 2:
- Fixed Bias: 0.5 M\Omega max
- Cathode Bias: 1.0 M\Omega max
Pentode Unit:
- Fixed Bias: 1.0 M\Omega max
- Cathode Bias: 1.0 M\Omega max

Direct Interelectrode Capacitances

The direct interelectrode capacitances of the 15BD11 are measured without an external shield.

Triode Unit No. 1

Grid to Plate: 1.9 pF
Input (Grid to Cathodes, Pentode Cathode, Pentode Grid 3, Heater, and Internal Shield): 3.0 pF
Output (Plate to Cathodes, Pentode Cathode, Pentode Grid 3, Heater, and Internal Shield): 2.2 pF

Triode Unit No. 2

Grid to Plate: 3.6 pF
Input (Grid to Triode 2 Cathode, Pentode Cathode, Pentode Grid 3, Heater, and Internal Shield): 2.4 pF
Output (Plate to Triode 2 Cathode, Pentode Cathode, Pentode Grid 3, Heater, and Internal Shield): 3.8 pF

Pentode Unit

Grid No. 1 to Plate: 0.13 pF
Input (Grid No. 1 to Triode 2 Cathode, Pentode Cathode, Pentode Grid 2, Pentode Grid 3, Heater, and Internal Shield): 11 pF
Output (Plate to Triode 2 Cathode, Pentode Cathode, Pentode Grid 2, Pentode Grid 3, Heater, and Internal Shield): 4.6 pF

Inter-Section Coupling Capacitances

Pentode Plate to Triode Unit No. 2 Plate: 0.045 pF max
Triode Unit No. 1 Plate to Triode Unit No. 2 Plate: 0.075 pF max

Technical Summary

The 15BD11 is a versatile, multi-unit Compactron tube designed for television receiver circuits. By integrating a high-mu triode, a medium-mu triode, and a high-transconductance sharp-cutoff pentode into a single T-9 envelope, it reduces component count and space requirements. Operating with a 14.7 V, 0.450 A heater, it is optimized for series-string heater chains. The independent cathodes and low inter-section coupling capacitances ensure that each section can operate reliably in its respective role as a general-purpose amplifier, sync separator, or video amplifier.

Socket description

Duodecar 12-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: 12DP
Socket code: B12C
Base pins: 12
Nominal heater voltage: 14.7 V
Nominal heater current: 450 mA
Parallel heater voltage: -
Parallel heater current: -
Series capable: No

12DP - 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

Triode

X-ray radiationInterelectrode capacitances

Plate resistance: 40000 Ω
Transconductance: 0.0025 S
Amplification factor: 70
Max plate voltage: 330 V
Max plate dissipation: 1.5 W

triode 1

Section 2

Triode

X-ray radiationInterelectrode capacitances

Plate resistance: 10000 Ω
Transconductance: 0.005 S
Amplification factor: 30
Max plate voltage: 330 V
Max plate dissipation: 2 W

triode 2

Section 3

Pentode

X-ray radiationInterelectrode capacitances

Plate resistance: 70000 Ω
Transconductance: 0.012 S
Max plate voltage: 330 V
Max screen voltage: 330 V
Max plate dissipation: 5 W
Max screen dissipation: 1.5 W

sharp-cutoff

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

1971 RCA HB3 Binder 5 of 7

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

Maximum Plate Voltage
330 V
Inherited from explicitly referenced 6BD11 parent except heater data.
Plate Dissipation
1.5 W
Inherited from explicitly referenced 6BD11 parent except heater data.

Characteristics

Amplification Factor
70
Inherited from explicitly referenced 6BD11 parent except heater data.
Transconductance
2500 µS
Inherited from explicitly referenced 6BD11 parent except heater data.

SECTION 2

Triode

Other

Maximum Plate Voltage
330 V
Inherited from explicitly referenced 6BD11 parent except heater data.
Plate Dissipation
2 W
Inherited from explicitly referenced 6BD11 parent except heater data.

Characteristics

Amplification Factor
30
Inherited from explicitly referenced 6BD11 parent except heater data.
Transconductance
5000 µS
Inherited from explicitly referenced 6BD11 parent except heater data.

SECTION 3

Pentode

Other

Maximum Plate Voltage
330 V
Inherited from explicitly referenced 6BD11 parent except heater data.
Maximum Screen Voltage
330 V
Inherited from explicitly referenced 6BD11 parent except heater data.
Plate Dissipation
5 W
Inherited from explicitly referenced 6BD11 parent except heater data.
Screen Dissipation
1.5 W
Inherited from explicitly referenced 6BD11 parent except heater data.

Characteristics

Transconductance
12000 µS
Inherited from explicitly referenced 6BD11 parent except heater data.