Data set 01
1939 Arcturus
Published operating points and test conditions from this source.
SECTION 1
Triode
Other
Plate voltage
250 V
Control-grid voltage
-3 V
Plate current
1.7 mA
Voltage - Triode (with diode, heptode or hexode) ·Diode-Diode-Triode
12Q7GT
GT-envelope double-diode high-mu triode for detector, AVC, and audio voltage-amplifier service. Two diode sections handle signal and control rectification while the triode provides substantial subsequent gain.
Directly heatedCold cathodeCommon cathodeDissimilar
- Sections
- 3
- Base
- 7V
- Socket code
- IO
- Base pins
- 8
- Nominal heater
- 12.6 V / 150 mA
Description
12Q7GT — Duplex-Diode High-Mu Triode
The 12Q7GT is an indirectly heated, multi-unit vacuum tube containing two diode plates and a single high-mu triode system sharing a common unipotential cathode. Designed primarily for series-string heater operation in AC/DC radio receivers, the tube functions as a combined diode detector, automatic volume control (AVC) rectifier, and low-frequency (L.F.) or high-gain resistance-coupled amplifier.
Construction, Heater, and Base Pinout
The 12Q7GT is constructed in a glass envelope (typically a T-9 bulb) with a small wafer 7-pin octal base featuring a metal shell. The internal structure utilizes a unipotential cathode that is common to both the triode and the two diode units.
The heater is designed for series-string operation, drawing a low current to minimize overall power consumption and eliminate the need for bulky series drop resistors or specialized line cords in AC/DC receiver designs.
| Heater Parameter | Value |
|---|---|
| Heater Voltage | 12.6 V (or 12.5 V in early registrations) |
| Heater Current | 0.15 A (150 mA) |
| Heater Supply | AC or DC |
Pin Connection Configuration
Viewed from the bottom of the base, the 12Q7GT utilizes the following pinout (basing arrangement 7V):
- Pin 1: No Connection (NC) — internally connected to the metal shell
- Pin 2: Heater (H)
- Pin 3: Triode Anode / Plate (A)
- Pin 4: Diode Plate 2 (D2)
- Pin 5: Diode Plate 1 (D1)
- Pin 6: No Pin (NP)
- Pin 7: Heater (H)
- Pin 8: Cathode (K)
- Top Cap: Triode Control Grid (G)
Physical Dimensions
- Maximum Diameter: 1 5/16 inches
- Maximum Seated Height: 2 3/8 inches
- Maximum Overall Height: 2 7/8 to 3 5/16 inches (including pins and top cap)
Electrical Characteristics and Class A Operation
The triode section of the 12Q7GT is characterized by a high amplification factor, making it highly effective for voltage amplification. The typical operating parameters vary depending on the applied plate voltage and grid bias:
| Parameter | Operating Point A | Operating Point B | Operating Point C |
|---|---|---|---|
| Plate Voltage | 100 V | 100 V | 250 V |
| Control Grid Voltage | 0 V | -1 V | -3 V |
| Plate Current | 2.3 mA | 0.8 mA | 1.0 to 1.1 mA |
| Plate Resistance | 43,000 Ω | 58,000 Ω | 58,000 Ω |
| Transconductance | 1,400 µmhos | 1,200 µmhos | 1,200 µmhos (1.2 mA/V) |
| Amplification Factor | 60 | 70 | 70 |
Maximum Ratings
- Maximum Plate Voltage: 300 Volts
- Minimum Diode Current: 0.8 mA per plate with 10 Volts DC applied
Resistance-Coupled Amplifier Service
In typical receiver applications, the triode section of the 12Q7GT is operated as a zero-bias, resistance-coupled Class A1 amplifier. Under these conditions, the tube delivers high voltage gain with minimal distortion.
| Circuit Parameter | 100 V Supply | 300 V Supply |
|---|---|---|
| Plate Supply Voltage | 100 V | 300 V |
| Plate Load Resistor | 0.25 MΩ | 0.25 MΩ |
| Grid Resistor | 10 MΩ | 10 MΩ |
| Coupling Condenser | 0.01 to 0.005 µf | 0.01 to 0.005 µf |
| Following Stage Grid Resistor | 0.5 to 1.0 MΩ | 0.5 to 1.0 MΩ |
| External Grid Circuit Impedance | 0 Ω | 0 Ω |
| Voltage Gain | 40 to 42 | 50 to 56 |
| Voltage Output (RMS) * | 11 to 13 V | 51 to 58 V |
Interelectrode Capacitances
The direct interelectrode capacitances of the 12Q7GT are documented both with and without an external shield. Standard registrations list the following typical values without an external shield:
- Grid to Plate: 1.6 to 1.7 µµf
- Input (Grid to Cathode + Heater): 1.7 to 2.2 µµf
- Output (Plate to Cathode + Heater): 3.5 to 5.0 µµf
To prevent unwanted coupling between the triode and diode sections, reregistration specifications establish the following maximum limits:
- Triode Grid to Diode Plate 2 (Max): 0.001 µµf
- Triode Grid to Diode Plate 1 (Max): 0.001 µµf
- Diode Plate 2 to Heater + Cathode + Pin 1: 1.7 µµf
- Diode Plate 1 to Heater + Cathode + Pin 1: 2.2 µµf
Relationship to Other Tubes
The electrical characteristics, ratings, and physical dimensions of the 12Q7GT are identical to those of the 6Q7GT, with the sole exception of the heater rating. The 6Q7GT operates on a 6.3 V, 0.3 A heater supply, whereas the 12Q7GT is optimized for 12.6 V, 0.15 A series-string operation. Consequently, technical references and characteristic curves published for the 6Q7GT are directly applicable to the triode and diode units of the 12Q7GT.
Technical Summary
The 12Q7GT is an octal-based, duplex-diode high-mu triode designed for detection, AVC, and audio-frequency voltage amplification in AC/DC series-heater receivers. Operating with a 12.6 V, 0.15 A heater, it features a common unipotential cathode and a 7-pin octal base with an internal connection between Pin 1 and its metal shell. The triode section provides an amplification factor of 70, a plate resistance of 58,000 Ω, and a transconductance of 1,200 µmhos under typical 250 V Class A operating conditions. When configured as a resistance-coupled amplifier, it achieves a voltage gain of up to 56, making it a highly efficient single-tube solution for the detector and preamplifier stages of superheterodyne receivers.
Socket description
International Octal
General specifications
Tube and section characteristics
Properties common to every published source and operating point.
Heater and base
- Base
- 7V
- 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
7V - 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
- 58000 Ω
- Transconductance
- 0.0012 S
- Amplification factor
- 70
- Max plate voltage
- 300 V
Published section data promoted where applicable; additional operating values retained as parameters.
Section 2
Diode
X-ray radiationInterelectrode capacitances
No fixed ratings are recorded for this section.
Published section data promoted where applicable; additional operating values retained as parameters.
Section 3
Diode
X-ray radiationInterelectrode capacitances
No fixed ratings are recorded for this section.
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 02
1948 Brimar Radio Valve Manual
Published operating points and test conditions from this source.
SECTION 1
Triode
Characteristics
Anode Voltage
250 V
Anode Current
1.1 mA
Grid Voltage
-3 V
Data set 03
195X General Electric Essential Characteristics
Published operating points and test conditions from this source.
SECTION 1
Triode
Capacitance
Input capacitance
2.2 pF
Section1
Output capacitance
5 pF
Section1
Grid-to-plate capacitance
1.6 pF
Section1
Other
Plate voltage
250 V
ClassA
Control-grid voltage
-3 V
ClassA
Plate current
1 mA
ClassA
Characteristic
Plate resistance
58000 Ω
Section1
Transconductance
1200 µS
Section1
Amplification factor
70
Section1
Data set 04
1961 Ferranti Technical Handbook
Published operating points and test conditions from this source.
SECTION 1
Triode
Application
Application
AF amplifier
SECTION 2
Diode
Application
Application
Detector / AVC