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Voltage Radio Detector Converter ·Heptode

12SY7GT

GT-envelope heptode oscillator-converter for superheterodyne receivers. Its multi-grid structure combines local oscillation and mixing, translating incoming radio-frequency signals to the intermediate frequency while providing useful isolation between input and oscillator circuits.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 1
Base: 8ADV
Socket code: IO
Base pins: 8
Nominal heater: 12.6 V / 150 mA

Description

12SY7GT — Heptode Pentagrid Converter

The 12SY7GT (also referenced as the 12SY7) is an indirectly heated heptode pentagrid converter vacuum tube designed for frequency converter service in superheterodyne radio receivers. It is engineered to operate either with separate excitation or in a self-excited oscillator circuit. Featuring a unipotential coated cathode and a 12.6 V heater, the tube is well-suited for series-string heater chains or applications utilizing a 12 V electrical supply.

Physical Specifications and Base Connections

The 12SY7GT is constructed in a T-9 glass bulb with an 8-pin small wafer octal base featuring a metal shell. The physical dimensions of the device are as follows:

Maximum Diameter: 1 5/16 inches
Maximum Overall Length: 3 5/16 inches
Maximum Seated Height: 2 3/4 inches
Mounting Position: Any

The octal base connections, viewed from the bottom of the tube, conform to the following pinout:

Pin	Connection
Pin 1	Base Shell
Pin 2	Heater
Pin 3	Plate
Pin 4	Screen (Grids G2 and G4)
Pin 5	Oscillator Grid (Grid G1)
Pin 6	Cathode, Grid G5, and Internal Shield (K, G5, SI)
Pin 7	Heater
Pin 8	Signal Grid (Grid G3)

Electrical Ratings and Capacitances

The maximum ratings for the 12SY7GT are established under the RMA Standard MB-210. These values represent the absolute limits for reliable operation:

Heater Voltage (AC or DC): 12.6 V
Heater Current: 0.15 A
Calculated Heater Power: 1.89 W
Maximum Plate Voltage: 300 V
Maximum Screen Voltage (Grids G2 & G4): 100 V
Maximum Screen Supply Voltage: 300 V
Maximum Plate Dissipation: 1.0 W
Maximum Screen Dissipation: 1.0 W
Maximum Total Cathode Current: 14 mA
Minimum External Signal Grid Bias Voltage (Grid G3): 0 V (with self-excited oscillator)

Interelectrode Capacitances

The capacitances of the 12SY7GT are measured with the base shell and a standard tube shield connected directly to the cathode:

Signal Grid to Mixer Plate (G3 to P): 0.2 µµF (maximum)
Signal Grid to Oscillator Grid (G3 to G1): 0.2 µµF (maximum)
Oscillator Grid to Mixer Plate (G1 to P): 0.2 µµF (maximum)
Cathode (K) to all other electrodes except G1: 30 µµF
Signal Input (G3 to all other electrodes): 11 µµF
Oscillator Input (G1 to all other electrodes): 8.0 µµF
Oscillator Grid (G1) to all other electrodes except K: 5 µµF
Mixer Output (P to all other electrodes): 12 µµF
Oscillator Grid to Cathode (G1 to K): 3.0 µµF

Typical Operating Conditions and Characteristics

In typical converter service with separate excitation, the 12SY7GT can be operated across a range of plate and screen voltages. The conversion transconductance characteristics correspond closely to those obtained with zero bias in a self-excited oscillator circuit.

The following table details the typical operating parameters at three distinct voltage levels:

Parameter	Low-Voltage Operation	Medium-Voltage Operation	High-Voltage Operation
Plate Voltage	28 V	100 V	250 V
Screen Voltage (G2 & G4)	28 V	100 V	100 V
Signal Grid Bias (G3)	-1 V	-2 V	-2 V
Anode-Grid Voltage (G5)	0 V	0 V	0 V
Plate Current	0.5 mA	3.3 mA	3.5 mA
Screen Current	1.8 mA	8.5 mA	8.5 mA
Oscillator-Grid Current (I_g1)	0.1 mA	0.5 mA	0.5 mA
Total Cathode Current	2.4 mA	12.3 mA	12.5 mA
Oscillator-Grid Resistor (R_g1)	20,000 Ω	20,000 Ω	20,000 Ω
Approximate Plate Resistance	—	0.5 MΩ	1.0 MΩ

Conversion Transconductance vs. Signal Grid Bias

The conversion transconductance ( $g_c$ ) varies significantly with the applied signal grid bias (Grid G3), providing the mechanism for automatic volume control (AVC) or manual gain control:

At Low-Voltage Operation (28 V Plate/Screen):
- $g_c$ at -1 V Bias: 250 µmhos
- $g_c$ at -6 V Bias: 8 µmhos
At Medium-Voltage Operation (100 V Plate/Screen):
- $g_c$ at -2 V Bias: 425 µmhos
- $g_c$ at -6 V Bias: 310 µmhos
- $g_c$ at -10 V Bias: 75 µmhos
- $g_c$ at -35 V Bias: 2 µmhos (approximate)
At High-Voltage Operation (250 V Plate / 100 V Screen):
- $g_c$ at -2 V Bias: 450 µmhos
- $g_c$ at -6 V Bias: 325 µmhos
- $g_c$ at -10 V Bias: 80 µmhos
- $g_c$ at -35 V Bias: 2 µmhos (approximate)

Special Test Configuration

A specific test configuration is defined to evaluate the basic triode-like characteristics of the oscillator section. In this test, the screen grids (G2 and G4) are connected directly to the plate, and a potential of 100 V is applied to this combined electrode. The signal grid (G3) is connected to ground, and the input signal is applied to the oscillator grid (G1) at 0 V bias. Under these conditions, the tube exhibits the following characteristics:

Transconductance: 4500 µmhos
Plate Current: 27 mA
Amplification Factor ( $\mu$ ): 13

Technical Summary

The 12SY7GT is a heptode pentagrid converter featuring a 12.6 V, 0.15 A heater and an 8-pin octal base with a metal shell. It is designed to perform frequency conversion in superheterodyne receivers, offering high plate resistance (up to 1.0 MΩ) and a conversion transconductance of up to 450 µmhos under typical high-voltage operating conditions. Its multi-grid structure allows for effective separation of the oscillator and mixer functions, while its remote-cutoff signal grid characteristic enables effective gain control over a wide range of input signal levels.

Socket description

International Octal

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: 8ADV
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

8ADV - 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: 0.00044 S
Max plate voltage: 200 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
28 V
ClassA
Screen voltage
28 V
ClassA
Control-grid bias
1 V
ClassA
Plate current
0.5 mA
ClassA
Screen current
1.8 mA
ClassA

Characteristic

Transconductance
250 µS
Published handbook characteristic
Heater voltage
12.6 V
Published heater rating
Heater current
150 mA
Published heater rating

Data set 02

1961 Tung Sol

Published operating points and test conditions from this source.

SECTION 1

Heptode

Characteristic

Conversion Transconductance
440 uS
ZeroGridBias