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Voltage Radio Detector Converter ·Diode-Pentode

12CR6

Combination diode-pentode for receiving-equipment detection and signal amplification. The diode provides detector or rectifying action while the pentode supplies useful voltage gain in series-heater receiver designs.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 2
Base: -
Socket code: B7G
Base pins: 7
Nominal heater: 12.6 V / 150 mA

Description

12CR6 — Diode-Remote-Cutoff Pentode

The 12CR6 is a multi-unit miniature vacuum tube containing a single detector diode and a remote cut-off pentode within a single envelope. Sharing a common unipotential cathode, these two distinct electrical systems are housed in a compact 7-pin miniature glass construction. The tube is primarily designed for service in automobile and AC-operated radio receivers, where it functions as a combined AM detector and automatic-volume-controlled (AVC) audio amplifier. By applying the AVC voltage directly to the control grid of the remote cut-off pentode section, overall receiver AVC performance is significantly enhanced.

Construction, Mechanical Specifications, and Pinout

The 12CR6 features an indirectly heated, coated unipotential cathode. The physical structure is enclosed in a T-5-1/2 glass bulb and utilizes a small-button miniature 7-pin base (JETEC No. E7-1). The tube is designed to operate reliably in any mounting position.

Mechanical Dimensions

Maximum Overall Length: 2-1/8 inches
Maximum Seated Length: 1-7/8 inches
Length from Base Seat to Bulb Top (excluding tip): 1-1/2 inches 3/32 inch
Maximum Diameter: 3/4 inch

Pin Connection Diagram (7EA Basing)

The 7EA basing arrangement provides the following connections, viewed from the bottom of the tube:

Pin Number	Electrode Connection
Pin 1	Cathode, Pentode Grid No. 3 (Suppressor Grid)
Pin 2	Diode Plate
Pin 3	Heater
Pin 4	Heater
Pin 5	Pentode Plate
Pin 6	Pentode Grid No. 2 (Screen Grid)
Pin 7	Pentode Grid No. 1 (Control Grid)

Heater Characteristics

The heater is designed for operation on either AC or DC power.

Nominal Heater Voltage: 12.6 V
Nominal Heater Current: 0.15 A
Calculated Heater Power: 1.89 W (calculated as 12.6 V * 0.15 A)

Pentode Unit Electrical Characteristics and Operating Points

The pentode section of the 12CR6 is characterized by its remote cut-off (super-control) characteristic, which allows it to handle a wide range of input signals without severe distortion when AVC bias is applied. Under typical Class A1 amplifier operating conditions, the pentode unit exhibits the following parameters:

Plate Voltage: 250 V
Grid No. 2 (Screen-Grid) Voltage: 100 V
Grid No. 1 (Control-Grid) Voltage: -2 V
Plate Current: 9.6 mA
Grid No. 2 Current: 2.6 mA
Transconductance: 2200 mhos
Plate Resistance (Approximate): 0.8 M̩
Grid No. 1 Voltage for transconductance of 10 mhos (Approximate): -32 V

The very low transconductance of 10 mhos at a grid bias of -32 V demonstrates the remote cut-off nature of the control grid, allowing the stage gain to be reduced smoothly over a wide range of negative bias voltages.

Maximum Ratings and Circuit Constraints

The maximum ratings for the 12CR6 are established under the Design-Center System. These limits must not be exceeded under the worst-case operating conditions to ensure device longevity and reliable performance.

Pentode Unit Ratings

Maximum Plate Voltage: 300 V
Maximum Grid No. 2 (Screen-Grid) Supply Voltage: 300 V
Maximum Grid No. 2 Voltage: 150 V (for grid No. 2 voltages up to 150 V, the maximum input is restricted; for voltages between 150 V and 300 V, reference must be made to specific input rating charts)
Maximum Positive DC Grid No. 1 Voltage: 0 V
Maximum Plate Dissipation: 2.5 W
Maximum Grid No. 2 Input: 0.3 W (for grid No. 2 voltages up to 150 V)
Maximum Grid No. 1 Circuit Resistance:
- For cathode-bias operation: 1.0 M̩
- For fixed-bias operation: 0.25 M̩

Diode Unit Ratings

Maximum Diode Plate Current: 1.0 mA

Heater-Cathode Ratings

Maximum Peak Heater-Cathode Voltage:
- Heater negative with respect to cathode: 100 V
- Heater positive with respect to cathode: 100 V

Diode Unit Characteristics

The diode unit of the 12CR6 is independent of the pentode unit except for the shared cathode connection. It is designed specifically for low-current detection duties, such as AM demodulation.

Minimum Diode Current: 2 mA (with 10 V DC applied directly to the diode plate)
Operation: The average plate characteristic of the diode unit shows a non-linear rectification curve. At low DC plate voltages, current starts near zero and rises gradually, reaching approximately 2 mA at 10 V DC, and continuing to rise to over 10 mA as the applied DC potential approaches 30 V. The maximum continuous diode plate current rating of 1.0 mA must be respected in practical detector circuit designs.

Characteristic Curves and Interpretation

The behavior of the 12CR6 is further illustrated by its average characteristic curves:

Plate Characteristics (Pentode Unit): At a constant screen-grid (Grid No. 2) potential of 100 V, the plate current curves show typical pentode behavior. Above a plate voltage of approximately 50 V, the plate current curves flatten out, indicating very high plate resistance (nominally 0.8 M̩). The spacing between the curves for equal steps of Grid No. 1 voltage (from 0 V down to -15 V and beyond) decreases progressively, which is the hallmark of a remote cut-off grid structure.
Transfer Characteristics: Plotting plate current and transconductance against Grid No. 1 voltage reveals a smooth, gradual decline in transconductance from its peak of 2200 mhos at -2 V bias down to a negligible 10 mhos at -32 V. This wide grid-bias range prevents cross-modulation and distortion when strong AVC signals are present.

Related Designations

The 12CR6 is closely related to the 6CR6 in its internal structure, application, and electrical characteristics, differing primarily in its heater rating. While the 12CR6 requires a 12.6 V, 0.15 A heater supply, the 6CR6 is designed for a 6.3 V heater supply. These two types are not directly interchangeable without modifying the heater supply circuit.

Technical Summary

The 12CR6 is a versatile 7-pin miniature glass tube combining a single AM detector diode and a remote cut-off pentode with a common unipotential cathode. Operating with a 12.6 V, 0.15 A heater, it is optimized for automobile and AC-operated radio receivers. The pentode section provides a transconductance of 2200 mhos and a high plate resistance of 0.8 M̩ under typical Class A1 conditions, with a remote cut-off characteristic extending to -32 V for effective AVC operation. The diode unit provides reliable detection with a maximum rated current of 1.0 mA.

Socket description

Miniature 7-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: -
Socket code: B7G
Base pins: 7
Nominal heater voltage: 12.6 V
Nominal heater current: 150 mA
Parallel heater voltage: -
Parallel heater current: -
Series capable: No

Terminal pinout

Electrical assignments shared by every tube using this base designation.

No verified pinout is recorded for this base designation.

Section ratings

2 physical sections, each with unique specifications.

Section 1

Diode

X-ray radiationInterelectrode capacitances

No fixed ratings are recorded for this section.

Promoted values are limited to values explicitly present in this supplied 12-V datasheet block; additional published values are retained in parameter rows.

Section 2

Pentode

X-ray radiationInterelectrode capacitances

Plate resistance: 800000 Ω
Transconductance: 0.0022 S
Max plate voltage: 300 V
Max screen voltage: 300 V
Max plate dissipation: 2.5 W
Max screen dissipation: 0.3 W

Promoted values are limited to values explicitly present in this supplied 12-V datasheet block; additional published values are retained in parameter rows.

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

1961 Tung Sol

Published operating points and test conditions from this source.

SECTION 1

Diode

Other

Heater voltage
12.6 V
Nominal
Heater current
150 mA
Nominal

Data set 02

1966 Tung Sol Electronic Tubes 2 of 4

Published operating points and test conditions from this source.

SECTION 1

Diode

Characteristic

Minimum diode current at 10 V applied
2 mA
DiodeSection

Other

Maximum heater-cathode voltage
100 V
WholeTube

SECTION 2

Pentode

Other

Plate voltage
250 V
ClassA1
Screen voltage
200 V
ClassA1
Grid 1 voltage
-2 V
ClassA1
Plate current
9.6 mA
ClassA1
Screen current
2.6 mA
ClassA1

Characteristic

Grid 1 voltage for 10 µS transconductance
-12 V
ClassA1

Data set 03

1971 RCA HB3 Binder 5 of 7

Published operating points and test conditions from this source.

SECTION 1

Diode

Characteristics

Voltage
12.6 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Current
150 mA
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Pin 2 -Diode
2
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Pin 3 -Heater
3
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Pin 4 -Heater
4
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
For grid-No.2 voltages between 150
150 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
and 300 volts
300 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Plate 4oltage — published value 1
4 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Plate 4oltage — published value 2
250 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Grid-No.-2 Voltage — published value 1
2 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Grid-No.-2 Voltage — published value 2
100 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Grid-No.l Voltage
-2 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Plate Resistance (Approx.)
0.8 Mohm
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Transconductance
2200
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Current
9.6 mA
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Current
2.6 mA
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
GRID—NQ2 VOLTS=100
100 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
GRID-N42 VOLTS=100 — published value 1
100 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
GRID-N42 VOLTS=100 — published value 2
2600 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
150 mA
Nominal heater rating

Other

PLATE VOLTAGE
300 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
GRID-No.2 (SCREEN-GRID) SUPPLY VOLTAGE
300 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Positive bias value
0 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
PLATE DISSLPATION
2.5 mA
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
For grid-No.2 voltages up to 150 volts — published value 1
150 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
For grid-No.2 voltages up to 150 volts — published value 2
0.3 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Heater negative with respect to cathode
100 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Heater positive with respect to cathode
100 V
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
cathode-bias operation
1 mA
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
fixed-bias operation — published value 1
0 mA
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
fixed-bias operation — published value 2
25 mA
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
CURRENT
1 mA
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

SECTION 2

Pentode

Characteristics

Pin 1 -Cathode, — published value 1
1
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Pin 1 -Cathode, — published value 2
5
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Grid No.3
6
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.
Plate
7
Published value from the filename-designated RCA datasheet block; multiple numbers on one row represent separate limits or heater arrangements.

Other

Maximum screen-grid input
0.3 W
PublishedOn12VSheet