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Power - Beam (NOT sweep) ·BeamPower-Pentode

12BF11

Multi-section television receiving tube incorporating a beam-power audio output stage with an additional small-signal section for receiver amplification or control functions.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 2
Base: 12EZ
Socket code: B12C
Base pins: 12
Nominal heater: 12.6 V / 600 mA

Description

12BF11 — Dual-Control Sharp-Cutoff Pentode and Beam Power Tube

An indirectly heated, multi-unit duodecar vacuum tube combining a dual-control sharp-cutoff pentode and a beam power amplifier in a single envelope, designed for television receiver applications.

Overview

The 12BF11 is a multi-unit glass vacuum tube of the duodecar (or Compactron T-9) family. It integrates two distinct, electrically independent operating sections: a dual-control, sharp-cutoff pentode unit and a high-sensitivity beam power unit. This combination is specifically tailored for television receiver designs, where the pentode unit serves as an FM sound detector and the beam power unit operates as the audio frequency (AF) output amplifier.

The 12BF11 belongs to a family of identical tubes that differ only in their heater ratings. This family includes the 6BF11, 17BF11, and 24BF11. The shared internal structure and electrode configurations allow these types to be used interchangeably in terms of signal circuitry, provided the power supply accommodates their respective heater requirements.

Construction, Heater, and Pinout

The 12BF11 is constructed in a Compactron T-9 glass envelope with a 12-pin button base (E12-70). It requires a standard duodecar 12-contact socket and can be operated in any mounting position. The physical dimensions of the tube include a maximum diameter of 1.188 inches, a maximum seated height of 2.250 inches, and a maximum overall height of 2.625 inches.

The cathodes of both units are indirectly heated, coated unipotential structures. The heater is designed with a controlled warm-up time of 11 seconds to facilitate series-string operation in television receivers.

Heater Characteristics and Ratings

The heater specifications for the 12BF11 and its sister types are as follows:

Tube Designation	Heater Voltage (AC/DC)	Heater Current	Average Warm-up Time
6BF11	6.3 V	1.2 A (1200 mA)	—
12BF11	12.6 V	0.600 ± 0.040 A	11 seconds
17BF11	16.8 V	0.45 A (450 mA)	11 seconds
24BF11	24.2 V	0.315 A (315 mA)	11 seconds

Heater-Cathode Voltage Limits

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

Peak value: ±200 V maximum
Average value: 100 V maximum

Pin Connections (12EZ Basing Diagram)

The 12EZ basing arrangement provides the following pin connections, viewed from the underside of the tube:

Pin Number	Electrode Connection
1	Grid No. 1 of Beam Power Unit (G1b)
2	Cathode of Pentode Unit, Internal Shield (Kp, IS)
3	Grid No. 1 of Pentode Unit (G1p)
4	No Connection (NC)
5	Grid No. 3 of Pentode Unit (G3p)
6	Grid No. 2 of Pentode Unit (G2p)
7	Plate of Pentode Unit (Pp)
8	Plate of Beam Power Unit (Pb)
9	Cathode and Grid No. 3 of Beam Power Unit (Kb, G3b)
10	Grid No. 2 of Beam Power Unit (G2b)
11	Heater (H)
12	Heater (H)

Direct Interelectrode Capacitances

The unshielded direct interelectrode capacitances of the 12BF11 reflect the isolation between the two internal units as well as the internal shielding.

Unit / Electrodes	Capacitance Value
Pentode Unit (Section 2)
Grid No. 1 to Plate (Max.)	0.036 pF
Grid No. 3 to Plate	3.2 pF
Grid No. 1 to Cathode, Heater, Grid No. 2, Grid No. 3, and Internal Shield	6.5 pF
Grid No. 3 to Cathode, Heater, Grid No. 1, Grid No. 2, Plate, and Internal Shield	8.0 pF
Grid No. 1 to Grid No. 3	0.11 pF
Beam Power Unit (Section 1)
Grid No. 1 to Plate	0.24 pF
Grid No. 1 to Cathode, Heater, Grid No. 2, Grid No. 3, and Internal Shield	13.0 pF
Plate to Cathode, Heater, Grid No. 2, Grid No. 3, and Internal Shield	10.0 pF
Inter-Unit Coupling
Pentode Plate to Beam Power Plate	0.13 pF

Beam Power Unit (Section 1) Characteristics and Class A1 Operation

The beam power unit is designed to operate as a high-sensitivity Class A1 audio power amplifier. It features high transconductance and moderate plate dissipation capabilities.

Maximum Ratings (Design-Maximum Values)

Plate Voltage: 165 V
Grid-No. 2 (Screen-Grid) Voltage: 150 V
Average Cathode Current: 65 mA
Plate Dissipation: 6.5 W
Grid-No. 2 Input: 1.8 W

Typical Operating Conditions

At a typical operating point, the beam power unit delivers up to 2.4 watts of audio output with 10% total harmonic distortion:

Plate Voltage: 145 V
Grid-No. 2 Voltage: 110 V
Grid-No. 1 (Control-Grid) Voltage: -6.0 V
Peak AF Grid-No. 1 Voltage: 6.0 V
Zero-Signal Plate Current: 36 mA
Maximum-Signal Plate Current: 40 mA
Zero-Signal Grid-No. 2 Current: 3.0 mA
Maximum-Signal Grid-No. 2 Current: 9.0 mA
Plate Resistance (Approx.): 30,000 Ω (0.03 MΩ)
Transconductance: 8600 µmhos
Load Resistance: 3000 Ω (Note: Some documentation lists 30,000 Ω, though 3000 Ω is typical for this class of power amplifier)
Total Harmonic Distortion (Approx.): 10%
Maximum-Signal Power Output: 2.4 W

Maximum Circuit Values

Grid-No. 1-Circuit Resistance (Fixed Bias): 0.25 MΩ
Grid-No. 1-Circuit Resistance (Cathode Bias): 0.5 MΩ

Pentode Unit (Section 2) Characteristics and Operation

The pentode unit is a dual-control, sharp-cutoff device. It is designed to operate either as a Class A1 amplifier or as an FM sound detector.

Typical Operation as Class A1 Amplifier

When operated as a Class A1 amplifier, the pentode unit exhibits the following characteristics:

Plate Supply Voltage: 150 V
Grid-No. 3 (Control-Grid) Voltage: Connected to negative end of cathode resistor
Grid-No. 2 (Screen-Grid) Supply Voltage: 100 V
Grid-No. 1 (Control-Grid) Voltage: Connected to negative end of cathode resistor
Cathode-Bias Resistor: 560 Ω
Plate Resistance (Approx.): 150,000 Ω (0.15 MΩ)
Transconductance, Grid No. 1 to Plate: 1000 µmhos
Transconductance, Grid No. 3 to Plate: 400 µmhos
Plate Current: 1.3 mA
Grid-No. 2 Current: 2.0 mA (or 2.1 mA)
Grid-No. 1 Voltage (Approx.) for plate current of 10 µA: -4.5 V (Sylvania lists -4.5 V for 30 µA plate current)
Grid-No. 3 Voltage (Approx.) for plate current of 10 µA: -4.5 V (Sylvania lists -4.5 V for 50 µA plate current)

Maximum Ratings as FM Sound Detector (Design-Maximum Values)

Plate Voltage: 330 V
Grid-No. 3 (Suppressor) Voltage: 28 V
Grid-No. 2 Supply Voltage: 330 V
Grid-No. 1 (Control-Grid) Voltage, Positive-bias value: 0 V
Plate Dissipation: 1.7 W
Grid-No. 2 Input:
- For Grid-No. 2 voltages up to 165 V: 1.1 W
- For Grid-No. 2 voltages between 165 V and 330 V: Dependent on circuit curves

Maximum Circuit Values

Grid-No. 1-Circuit Resistance (Fixed Bias): 0.25 MΩ
Grid-No. 1-Circuit Resistance (Cathode Bias): 0.5 MΩ

Characteristic Curves and Qualitative Analysis

The published characteristic curves for the 12BF11 provide insights into the behavior of both units under varying voltage and bias conditions.

Beam Power Unit Curves

The plate characteristics for the beam power unit are plotted at a fixed screen-grid (Grid-No. 2) voltage of 110 V. The curves show plate current and screen-grid current as a function of plate voltage for control-grid (Grid-No. 1) voltages ranging from 0 V down to -12 V.

At low plate voltages (below 50 V), the plate current rises sharply, demonstrating the typical knee characteristic of beam power tubes.
The screen-grid current is highest at low plate voltages and drops to a low, stable value (around 3 mA to 9 mA depending on bias) once the plate voltage exceeds the knee.
The relatively flat plate current curves in the active region (above 100 V) indicate high plate resistance and stable gain.

Pentode Unit Curves

The plate characteristics for the pentode unit are plotted at a fixed suppressor-grid (Grid-No. 3) voltage of 0 V and a screen-grid (Grid-No. 2) voltage of 100 V. The curves show plate current as a function of plate voltage for control-grid (Grid-No. 1) voltages from 0 V to -4 V.

The pentode curves exhibit a very sharp knee, typical of sharp-cutoff pentodes.
Above approximately 100 V, the plate current is highly independent of plate voltage, confirming the high plate resistance (approximately 0.15 MΩ) of this unit.
The dual-control nature of the pentode allows Grid No. 3 to also exert significant control over the plate current, making it highly suitable for FM detection where two separate control signals are applied.

Technical Summary

The 12BF11 is a versatile, multi-unit duodecar/Compactron vacuum tube containing a dual-control sharp-cutoff pentode and a beam power amplifier in a single T-9 glass envelope. Operating with a 12.6 V, 0.6 A heater with an 11-second warm-up time, it is designed for series-string television receivers.

The beam power unit provides up to 2.4 W of audio output under typical Class A1 conditions with a transconductance of 8600 µmhos. The pentode unit offers dual-control characteristics with a Grid-No. 1 transconductance of 1000 µmhos and a Grid-No. 3 transconductance of 400 µmhos, making it highly effective as an FM sound detector. By combining these two functions, the 12BF11 reduces tube count and simplifies chassis design in television audio systems.

Socket description

Duodecar 12-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: 12EZ
Socket code: B12C
Base pins: 12
Nominal heater voltage: 12.6 V
Nominal heater current: 600 mA
Parallel heater voltage: -
Parallel heater current: -
Series capable: No

12EZ - Terminal pinout

Electrical assignments shared by every tube using this base designation.

Terminal	Section	Connection	Evidence
PIN1Pin 1	—	H — Heater	Verified GE 12AE10 terminal connections 12EZ, 1968
PIN2Pin 2	B	K — CathodeGroup EZ2	Verified GE 12AE10 terminal connections 12EZ, 1968
PIN2Pin 2	B	SH — Internal ShieldGroup EZ2	Verified GE 12AE10 terminal connections 12EZ, 1968
PIN3Pin 3	B	G1 — Control Grid	Verified GE 12AE10 terminal connections 12EZ, 1968
PIN4Pin 4	—	NC	Verified GE 12AE10 terminal connections 12EZ, 1968
PIN5Pin 5	B	G3 — Suppressor Grid	Verified GE 12AE10 terminal connections 12EZ, 1968
PIN6Pin 6	B	G2 — Screen Grid	Verified GE 12AE10 terminal connections 12EZ, 1968
PIN7Pin 7	B	P — Plate (Anode)	Verified GE 12AE10 terminal connections 12EZ, 1968
PIN8Pin 8	A	G1 — Control Grid	Verified GE 12AE10 terminal connections 12EZ, 1968
PIN9Pin 9	A	BP — Beam-Forming PlateGroup EZ9	Verified GE 12AE10 terminal connections 12EZ, 1968
PIN9Pin 9	A	K — CathodeGroup EZ9	Verified GE 12AE10 terminal connections 12EZ, 1968
PIN10Pin 10	A	G2 — Screen Grid	Verified GE 12AE10 terminal connections 12EZ, 1968
PIN11Pin 11	A	P — Plate (Anode)	Verified GE 12AE10 terminal connections 12EZ
PIN12Pin 12	—	H — Heater	Verified GE 12AE10 terminal connections 12EZ

Section ratings

2 physical sections, each with unique specifications.

Section 1

Pentode

X-ray radiationInterelectrode capacitances

Plate resistance: 30000 Ω
Transconductance: 0.0086 S
Max plate voltage: 330 V
Max screen voltage: 330 V
Max plate dissipation: 1.7 W
Max screen dissipation: 1.1 W
Max cathode current: 65 A

Supplied sheet explicitly states this is the same as 6BF11 except for heater characteristics. Parent electrical table was not present in the currently available local corpus, so no unsupported promoted values were invented.

Section 2

Beam Power

X-ray radiationInterelectrode capacitances

Plate resistance: 30000 Ω
Transconductance: 0.0086 S
Max plate voltage: 165 V
Max screen voltage: 150 V
Max plate dissipation: 6.5 W
Max screen dissipation: 1.8 W
Max cathode current: 65 mA

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

Pentode

Characteristics

Current — published value 1
0.6
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Current — published value 2
0.04
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Voltage (AC or DC) at 0.600 A — published value 1
0.6 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Voltage (AC or DC) at 0.600 A — published value 2
12.6 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Heater voltage
12.6 V
Nominal heater rating
Heater current
600 mA
Nominal heater rating

Data set 02

1975 RCA RC30

Published operating points and test conditions from this source.

SECTION 1

Pentode

Capacitance

Pentode Plate to Beam Power Plate
0.13 pF
Capacitance

Other

Maximum Plate Voltage
330 V
Section2;Promoted
Maximum Screen Voltage
330 V
Section2;Promoted
Maximum Plate Dissipation
1.7 W
Section2;Promoted
Maximum Screen Dissipation
1.1 W
Section2;Promoted

Characteristic

Plate Resistance
150000 ohm
Section2;Promoted
Transconductance
1000 uS
Section2;Promoted

SECTION 2

Beam Power

Other

Heater Warm-up Time (Average)
11 s
Other;PublishedValue1
Heater Warm-up Time (Average)
11 s
Other;PublishedValue2
Heater Warm-up Time (Average)
11 s
Other;PublishedValue3
Peak value
200 V
Other;PublishedValue1
Peak value
200 V
Other;PublishedValue2
Peak value
200 V
Other;PublishedValue3
Peak value
0 V
Other;PublishedValue4
Average value
100 V
Other;PublishedValue1
Average value
100 V
Other;PublishedValue2
Average value
100 V
Other;PublishedValue3
Average value
100 V
Other;PublishedValue4
Plate Voltage
165 V
MaximumRating
Grid-No
2 V
MaximumRating;PublishedValue1
Grid-No
150 V
MaximumRating;PublishedValue2
Average Cathode Current
65 mA
MaximumRating
Plate Dissipation
6.5 W
MaximumRating
Grid-No
2 W
MaximumRating;PublishedValue1
Grid-No
1.8 W
MaximumRating;PublishedValue2
Plate Voltage
145 V
TypicalOperation
Grid-No
2 V
TypicalOperation;PublishedValue1
Grid-No
110 V
TypicalOperation;PublishedValue2
Grid-No
1 V
TypicalOperation;PublishedValue1
Grid-No
-6 V
TypicalOperation;PublishedValue2
Peak AF Grid-No.l Voltage
6 V
TypicalOperation
Zero-Signal Plate Current
36 mA
TypicalOperation
Maximum-Signal Plate Current
40 mA
TypicalOperation
Zero-Signal Grid No
2 mA
TypicalOperation;PublishedValue1
Zero-Signal Grid No
3 mA
TypicalOperation;PublishedValue2
Maximum-Signal Grid-No
2 mA
TypicalOperation;PublishedValue1
Maximum-Signal Grid-No
9 mA
TypicalOperation;PublishedValue2
Plate Resistance (Approx.)
0.03 megohm
TypicalOperation
Transconductance
8600 uS
TypicalOperation
PLATE
92 V
TypicalOperation;PublishedValue1
PLATE
742 V
TypicalOperation;PublishedValue2
Load Resistance
3000 ohm
TypicalOperation
Total Harmonic Distortion
10 %
TypicalOperation
Maximum-Signal Power Output
2.4 W
TypicalOperation
For fixed-bias operation
0.25 megohm
MaximumCircuitValue
For cathode-bias operation
0.5 megohm
MaximumCircuitValue
Plate Voltage
330 V
MaximumRating
Grid-No
3 V
MaximumRating;PublishedValue1
Grid-No
28 V
MaximumRating;PublishedValue2
Grid No
2 V
MaximumRating;PublishedValue1
Grid No
330 V
MaximumRating;PublishedValue2
Grid-No.l (Control-Grid) Voltage, Positive-bias value
0 V
MaximumRating
Plate Dissipation
1.7 W
MaximumRating
For grid-No
2 V
MaximumRating;PublishedValue1
For grid-No
165 V
MaximumRating;PublishedValue2
For grid-No
1.1 V
MaximumRating;PublishedValue3
For grid-No
2 V
MaximumRating;PublishedValue1
For grid-No
165 V
MaximumRating;PublishedValue2
For grid-No
330 V
MaximumRating;PublishedValue3
For grid-No
300 V
MaximumRating;PublishedValue4
For fixed-bias operation
0.25 megohm
MaximumCircuitValue
For cathode-bias operation
0.5 megohm
MaximumCircuitValue
Maximum Plate Voltage
165 V
Section1;Promoted
Maximum Screen Voltage
150 V
Section1;Promoted
Maximum Plate Dissipation
6.5 W
Section1;Promoted
Maximum Screen Dissipation
1.8 W
Section1;Promoted
Maximum Cathode Current
65 mA
Section1;Promoted

Capacitance

Grid No.l to Plate
0.36 pF
Capacitance
Grid No
3 pF
Capacitance;PublishedValue1
Grid No
3.2 pF
Capacitance;PublishedValue2
and Internal Shield
8 pF
Capacitance
Grid No.l to Grid No
3 pF
Capacitance;PublishedValue1
Grid No.l to Grid No
0.11 pF
Capacitance;PublishedValue2
Grid No.l to Plate
0.24 pF
Capacitance
and Internal Shield
13 pF
Capacitance
and Internal Shield
10 pF
Capacitance

Characteristic

Plate Supply Voltage
150 V
Characteristic
Grid-No
2 V
Characteristic;PublishedValue1
Grid-No
100 V
Characteristic;PublishedValue2
Cathode-Bias Resistor
560 ohm
Characteristic
Plate Resistance (Approx.)
0.15 megohm
Characteristic
Transconductance, Grid No.l to Plate
1000 uS
Characteristic
Plate Current
1.3 mA
Characteristic
Grid-No
2 mA
Characteristic;PublishedValue1
Grid-No
2 mA
Characteristic;PublishedValue2
Grid-No.l Voltage (Approx.) for plate current of
10 V
Characteristic;PublishedValue1
Grid-No.l Voltage (Approx.) for plate current of
-4.5 V
Characteristic;PublishedValue2
Grid-No
3 V
Characteristic;PublishedValue1
Grid-No
10 V
Characteristic;PublishedValue2
Grid-No
-4.5 V
Characteristic;PublishedValue3
Plate Resistance
30000 ohm
Section1;Promoted
Transconductance
8600 uS
Section1;Promoted