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Voltage Radio Detector Converter ·Heptode

12SY7

Triode-heptode frequency converter for superheterodyne receivers. The triode supplies local oscillation while the heptode performs mixing, integrating oscillator and frequency-changing functions within one envelope for compact radio front ends.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
8RV
Socket code
IO
Base pins
8
Nominal heater
12.6 V / 150 mA

Description

12SY7 — Pentagrid Converter Vacuum Tube

The 12SY7 is a single-ended metal-shell pentagrid converter (also classified as a heptode pentagrid converter) designed primarily for superheterodyne receiver circuits. It is specifically engineered for operation in equipment powered by a 12-cell storage-battery supply, making it highly suitable for mobile, automotive, and specialized industrial applications where the supply voltage typically ranges from 24 to 28 volts. The 12SY7 features an indirectly heated, coated unipotential cathode and is electrically similar to the 6SA7, differing principally in its heater requirements.

Mechanical Specifications and Basing

The 12SY7 is constructed with a metal envelope (MT-8G bulb) and utilizes a small wafer octal 8-pin phenolic base. The tube is designed to operate reliably when mounted in any position.

Physical Dimensions

  • Maximum Overall Length: 2-5/8 inches
  • Maximum Seated Length: 2-1/16 inches
  • Maximum Diameter: 1-5/16 inches

Pin Connections (8R Basing Designation)

The 12SY7 uses the 8R basing arrangement, viewed from the bottom of the tube:

Pin NumberElectrode Connection
Pin 1Metal Shell, Grid No. 5 (Suppressor Grid)
Pin 2Heater
Pin 3Plate (Anode)
Pin 4Grids No. 2 & No. 4 (Screen Grid)
Pin 5Grid No. 1 (Oscillator Grid)
Pin 6Cathode
Pin 7Heater
Pin 8Grid No. 3 (Signal Grid / Control Grid)

Electrical Ratings and Capacitances

The maximum ratings are established under the design-center system. Operating the tube within these limits ensures optimal performance and longevity.

Maximum Ratings

  • Plate Voltage: 300 max. volts
  • Grids-No. 2 and No. 4 (Screen) Voltage: 100 max. volts
  • Grids-No. 2 and No. 4 Supply Voltage: 300 max. volts
  • Plate Dissipation: 1.0 max. watt
  • Grids-No. 2 & No. 4 Dissipation: 1.0 max. watt
  • Total Cathode Current: 14 max. mA
  • Grid-No. 3 (Control Grid) Voltage (Negative Bias): 50 max. volts
  • Grid-No. 3 (Control Grid) Voltage (Positive Bias): 0 max. volts
  • Minimum External Signal Grid Bias Voltage: 0 volts (with self-excited oscillator)
  • Peak Heater-Cathode Voltage (Heater Negative or Positive with respect to Cathode): 90 max. volts

Heater Characteristics

  • Heater Voltage (AC or DC): 12.6 volts
  • Heater Current: 0.15 amperes

Direct Interelectrode Capacitances

The capacitances below are measured with the metal shell connected to the cathode:

Electrode Pair / GroupCapacitance Value
Grid No. 3 to All Other Electrodes (RF Input)9.5 µµF
Plate to All Other Electrodes (Mixer Output)12.0 µµF
Grid No. 1 to All Other Electrodes (Oscillator Input)7.0 µµF
Grid No. 3 to Plate0.13 max. µµF
Grid No. 1 to Grid No. 30.15 max. µµF
Grid No. 1 to Plate0.06 max. µµF
Grid No. 1 to Shell, Grid No. 5, and All Except Cathode4.4 µµF
Grid No. 1 to Cathode2.6 µµF
Cathode to Shell, Grid No. 5, and All Except Cathode5.0 µµF

Typical Operating Conditions and Characteristics

The 12SY7 can be operated under separate excitation or self-excited oscillator configurations. The typical characteristics under separate excitation correspond closely to those obtained in a self-excited oscillator circuit operating with zero bias.

The tube is characterized across three distinct operating points, including a low-voltage condition optimized for 12-cell storage-battery systems (nominal 26.5 V to 28 V):

ParameterLow-Voltage PointMedium-Voltage PointHigh-Voltage Point
Plate Voltage26.5 V / 28 V100 V250 V
Screen Voltage (Grids No. 2 & 4)26.5 V / 28 V100 V100 V
Signal Grid Bias (Grid No. 3)-1 V-2 V-2 V
Anode-Grid Voltage0 V0 V0 V
Oscillator-Grid Resistor (Grid No. 1)20,000 Ω20,000 Ω20,000 Ω
Plate Current0.45 mA / 0.5 mA3.3 mA3.5 mA
Screen Current (Grids No. 2 & 4)1.7 mA / 1.8 mA8.5 mA8.5 mA
Oscillator-Grid Current (Grid No. 1)0.1 mA0.5 mA0.5 mA
Total Cathode Current2.25 mA / 2.4 mA12.3 mA12.5 mA
Plate Resistance (Approx.)—0.5 MΩ1.0 MΩ
Conversion Transconductance250 µmhos425 µmhos450 µmhos

Conversion Transconductance at Various Bias Levels

The conversion transconductance varies significantly with the negative bias applied to Grid No. 3 (Signal Grid):

  • At -6 V Bias: Conversion transconductance drops to approximately 8 µmhos at the low-voltage operating point, 310 µmhos at the 100 V point, and 320–325 µmhos at the 250 V point.
  • At -10 V Bias: Conversion transconductance is approximately 75 µmhos (100 V point) and 80 µmhos (250 V point).
  • At -35 V Bias (Cutoff): Conversion transconductance is reduced to approximately 2 µmhos for both the 100 V and 250 V operating points.

Non-Oscillating Transconductance Characteristics

When the tube is operated in a non-oscillating state with Grid No. 1 and Grids No. 2 & No. 4 connected directly to the plate, the transconductance between Grid No. 1 and the combined plate/screen structure is approximately 4500 µmhos. This measurement is taken under the following specific conditions:

  • Grids No. 1, No. 3, No. 5, and the metal shell are held at 0 volts.
  • Grids No. 2 & No. 4 and the plate are maintained at 100 volts.
  • Grid No. 3 is connected to ground. Under these test conditions, the plate current is 27 mA and the amplification factor is 13.

Operation Characteristics and Curves

The performance of the 12SY7 under low-voltage conditions (26.5 V plate and screen supply) is highly dependent on the bias of Grid No. 3 and the current flowing through Grid No. 1.

Conversion Transconductance vs. Grid No. 3 Voltage

At a plate and screen potential of 26.5 V and a Grid No. 1 current of 0.1 mA, the conversion transconductance peaks at approximately 270 to 280 µmhos when the Grid No. 3 bias is near -0.5 V. As the negative bias on Grid No. 3 increases, the conversion transconductance decreases smoothly, reaching near-zero levels (cutoff) at approximately -4 V.

Electrode Currents and Transconductance vs. Grid No. 1 Current

With a fixed Grid No. 3 bias of -1 V and a 26.5 V supply:

  • Cathode Current: Rises steadily from approximately 1.5 mA to 4.8 mA as Grid No. 1 current increases from 0 to 0.8 mA.
  • Screen Current (Grids No. 2 & 4): Increases in tandem with cathode current, rising from 1.2 mA to approximately 3.8 mA over the same range.
  • Plate Current: Remains low and relatively flat, fluctuating slightly between 0.3 mA and 0.5 mA.
  • Conversion Transconductance: Reaches its optimum value of approximately 260 µmhos at a Grid No. 1 current of 0.15 to 0.2 mA. Increasing the Grid No. 1 current further causes a gradual decline in conversion transconductance, falling to approximately 160 µmhos at 0.8 mA.

The characteristic curves of the 12SY7 are identical in form to those of the 6SA7, allowing the same graphical analysis techniques to be applied for circuit design.

Related Designations and Variations

The 12SY7 is closely related to several other vacuum tubes in the pentagrid converter family:

  • 12SY7-GT: A glass-envelope variant of the 12SY7. It features an 8ADV basing configuration and shares the same electrical characteristics and ratings as the metal-shell 12SY7.
  • 6SA7: The 6.3-volt equivalent of the 12SY7. Aside from the heater voltage (6.3 V vs. 12.6 V) and heater current (0.3 A vs. 0.15 A), the two tubes share identical electrical characteristics, and their performance curves are directly interchangeable.

Technical Summary

The 12SY7 is an octal-based, metal-shell pentagrid converter designed for frequency conversion and mixer service in superheterodyne receivers. Operating with a 12.6 V, 0.15 A heater, it is optimized for mobile and automotive systems running on 12-cell storage batteries. The tube features a unipotential cathode, a maximum plate voltage rating of 300 V, and a maximum screen voltage rating of 100 V.

At its typical high-voltage operating point (250 V plate, 100 V screen), the 12SY7 provides a conversion transconductance of 450 µmhos and a plate resistance of 1.0 MΩ. For low-voltage battery operation (26.5 V to 28 V), it delivers a conversion transconductance of 250 µmhos. The 12SY7 offers a robust, compact, and self-shielded solution for RF mixing and oscillation within a single envelope.

Socket description

International Octal

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
8RV
Socket code
IO
Base pins
8
Nominal heater voltage
12.6 V
Nominal heater current
150 mA
Parallel heater voltage
-
Parallel heater current
-
Series capable
No

8RV - Terminal pinout

Electrical assignments shared by every tube using this base designation.

No verified pinout is recorded for this base designation.

Section ratings

1 physical section, each with unique specifications.

Section 1

Heptode

X-ray radiationInterelectrode capacitances
Plate resistance
500000 Ω
Transconductance
0.00045 S
Max plate voltage
300 V
Max screen voltage
100 V
Max plate dissipation
1 W

Published promoted fields populated semantically; identical repeated sections compressed.

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

195X General Electric Essential Characteristics

Published operating points and test conditions from this source.

SECTION 1

Heptode

Other

  • Maximum plate voltage

    300 V

    Published handbook rating

  • Maximum screen voltage

    100 V

    Published handbook rating

  • Plate voltage

    250 V

    ClassA

  • Screen voltage

    100 V

    ClassA

  • Control-grid bias

    2 V

    ClassA

  • Plate current

    3.5 mA

    ClassA

  • Screen current

    8.5 mA

    ClassA

Characteristic

  • Plate resistance

    1000000 ohm

    Published handbook characteristic

  • Transconductance

    450 µS

    Published handbook characteristic

  • Heater voltage

    12.6 V

    Published heater rating

  • Heater current

    150 mA

    Published heater rating

Data set 02

1960 RCA Industrial and Communications Types

Published operating points and test conditions from this source.

SECTION 1

Heptode

Characteristic

  • HeaterOrFilamentVoltage

    12.6 V

  • HeaterOrFilamentCurrent

    150 mA

  • Conversion Transconductance

    450 uS

    PlateVoltage=250V

Data set 03

1961 Tung Sol

Published operating points and test conditions from this source.

SECTION 1

Heptode

Characteristic

  • Conversion Transconductance

    450 uS

    ZeroGridBias

Data set 04

1971 RCA HB3 Binder 3 of 7

Published operating points and test conditions from this source.

SECTION 1

Heptode

Characteristics

  • Voltage

    12.6 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Current

    0.15

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid No.3 to Al l Other Electrodes (RF Input)

    9.5

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Plate to All Other Electrodes (Mixer Output)

    12

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid No.1 to All Other Electrodes (Osc. Input)

    7

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid No.l to Cathode

    2.6

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Pin l~- Shel l, — published value 1

    0

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Pin l~- Shel l, — published value 2

    5

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid No.5

    6

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Pin 2 - Heater — published value 1

    2

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Pin 2 - Heater — published value 2

    7

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Pin 3 - Plate — published value 1

    3

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Pin 3 - Plate — published value 2

    8

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Pin 4 - Grids No.2 ~

    4

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Plate Voltage — published value 1

    26.5 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Plate Voltage — published value 2

    100 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Plate Voltage — published value 3

    250 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grids-No.2 & No.4 Voltage — published value 1

    26.5 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grids-No.2 & No.4 Voltage — published value 2

    100 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grids-No.2 & No.4 Voltage — published value 3

    100 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid-No.3 Voltage — published value 1

    -1 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid-No.3 Voltage — published value 2

    -2 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid-No.3 Voltage — published value 3

    -2 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid) Resistor — published value 1

    20000 ohm

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid) Resistor — published value 2

    20000 ohm

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid) Resistor — published value 3

    20000 ohm

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Plate Resistance (Approx.) — published value 1

    0.5 Mohm

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Plate Resistance (Approx.) — published value 2

    1 Mohm

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Conversion Transconductance — published value 1

    250

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Conversion Transconductance — published value 2

    425

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Conversion Transconductance — published value 3

    450

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Plate Current — published value 1

    0.45 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Plate Current — published value 2

    3.3 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Plate Current — published value 3

    3.5 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grids-No.2 & — published value 1

    1.7 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grids-No.2 & — published value 2

    8.5 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grids-No.2 & — published value 3

    8.5 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid-No.1 Current — published value 1

    0.1 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid-No.1 Current — published value 2

    0.5 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid-No.1 Current — published value 3

    0.5 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Total Cathode Current — published value 1

    2.25 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Total Cathode Current — published value 2

    12.3 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Total Cathode Current — published value 3

    12.5 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • at 0 volts; gritls No.2 and No.0 and plate at 100 volts. Under the — published value 1

    0 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • at 0 volts; gritls No.2 and No.0 and plate at 100 volts. Under the — published value 2

    100 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • same conditions, the plate current is 27 mill iamperes, and the

    27 A

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • With grid-N 0.3 Dias of -6 volts — published value 1

    0.3 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • With grid-N 0.3 Dias of -6 volts — published value 2

    -6 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • PLATE VOLTS=26.5

    26.5 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRIDS-N'28 N' 4 VOLTS =28.5 — published value 1

    28 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRIDS-N'28 N' 4 VOLTS =28.5 — published value 2

    4 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRIDS-N'28 N' 4 VOLTS =28.5 — published value 3

    28.5 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRID-N~ 7 MILLIAMPERES=O-t

    7 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRID- N' 7RESISTOR-OHMS=20000 — published value 1

    7 ohm

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRID- N' 7RESISTOR-OHMS=20000 — published value 2

    20000 ohm

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRID-N' 3 VOLTS

    3 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • PLATE VOLTS=26.5 — published value 1

    26.5 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • PLATE VOLTS=26.5 — published value 2

    9 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRIDS-N" 2b Ns4 VOLTS= 26.5 — published value 1

    2 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRIDS-N" 2b Ns4 VOLTS= 26.5 — published value 2

    26.5 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRIDS-N" 2b Ns4 VOLTS= 26.5 — published value 3

    9 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRID-N~ i RESISTOR -OHMS= 20000

    20000 ohm

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRID•N' 3VOLTS= - 1 — published value 1

    3 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRID•N' 3VOLTS= - 1 — published value 2

    1 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

Other

  • Grid No.3 to Plate — published value 1

    0 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid No.3 to Plate — published value 2

    13 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid No.1 to Grid No.3 — published value 1

    0 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid No.1 to Grid No.3 — published value 2

    15 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid No.l to Plate — published value 1

    0 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Grid No.l to Plate — published value 2

    6 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • PLATE VOLTAGE

    300 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRIDS-No.2 and No.4 (SCREEN) VOLTAGE

    100 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRIDS-No.2 and No.4 SUPPLY VCLTAGE

    300 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • PLATE DISSIPA710N

    1 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • GRIDS-No.2 & No.4 DISSIPATION

    1 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • TOTAL CATHODE CURRENT

    14 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Negative bias value

    50 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Positive bias value

    0 mA

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Heater negative with respect to cathode

    9 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.

  • Heater positive with respect to cathode

    90 V

    Published datasheet value; multiple numbers on one source row represent separate limits or operating conditions.