Voltage Pentode or Tetrode (under 100V) ·Heptode
Low-voltage heptode oscillator-converter for 12 V automobile radios. It combines mixer and local-oscillator functions while operating directly from the vehicle supply without conventional high-voltage B-plus.
The 12GA6 is a miniature heptode vacuum tube designed primarily to perform the combined functions of mixer and oscillator (pentagrid converter) in automobile radio receivers. It is specifically engineered to operate with its plate and screen voltages supplied directly from a 12-volt storage battery, eliminating the need for a high-voltage power supply.
The 12GA6 is constructed in a T-5 1/2 glass envelope with a miniature button 7-pin base (EIA 7CH / E7-1). It features a coated unipotential cathode and can be mounted in any position.
The heater is designed to operate from either an AC or DC supply, typically sourced from an automobile electrical system.
| Parameter | Value |
|---|---|
| Nominal Heater Voltage | 12.6 V |
| Nominal Heater Current | 0.15 A |
| Heater Voltage Range (Automobile Service) | 10.0 V to 15.9 V |
Under automobile service conditions, the heater voltage must not fall below 10.0 volts or exceed 15.9 volts. Operation near these extreme limits results in a sacrifice in performance at low voltages and a reduction in life expectancy at high voltages. Improved supply-voltage regulation significantly increases equipment reliability.
The 12GA6 uses a 7-pin miniature base with the following pin assignments (viewed from the bottom):
| Pin Number | Connection |
|---|---|
| Pin 1 | Grid Number 1 (Oscillator Grid) |
| Pin 2 | Cathode and Grid Number 5 (Suppressor Grid) |
| Pin 3 | Heater |
| Pin 4 | Heater |
| Pin 5 | Plate |
| Pin 6 | Grid Numbers 2 and 4 (Screen Grid) |
| Pin 7 | Grid Number 3 (Signal Grid) |
The ratings of the 12GA6 are established under the Design-Maximum System. These are limiting values of operating and environmental conditions that should not be exceeded under the worst probable conditions in a bogey tube.
| Rating | Value |
|---|---|
| Maximum Plate Voltage | 16 V |
| Maximum Screen Voltage (Grids #2 & #4) | 16 V |
| Maximum Positive DC Grid #3 Voltage | 0 V |
| Maximum Negative DC Grid #3 Voltage | 16 V |
| Maximum Heater-Cathode Voltage (Heater Positive) | 16 V |
| Maximum Heater-Cathode Voltage (Heater Negative) | 16 V |
| Maximum Grid #3 Circuit Resistance | 10 MΩ |
The 12GA6 is optimized for low-voltage operation, typically running directly from a nominal 12.6 V supply.
In typical converter service, the tube operates with the following parameters:
| Parameter | Value |
|---|---|
| Plate Voltage | 12.6 V |
| Screen Voltage | 12.6 V |
| Grid #3 Supply Voltage | 0 V |
| Grid #3 Resistor (Bypassed) | 2.2 MΩ |
| Grid #1 Voltage (RMS, approximate) | 1.6 V |
| Grid #1 Resistor | 33,000 Ω |
| Plate Resistance (approximate) | 1.0 MΩ |
| Conversion Transconductance | 140 µmhos |
| Plate Current | 0.30 mA |
| Screen Current | 0.80 mA |
| Grid #1 Current | 0.060 mA |
| Grid #3 Voltage for Gc = 5 µmhos (approximate) | -3 V |
| Grid #3 Voltage for Gc = 20 µmhos (approximate) | -2.5 V |
When evaluated for its oscillator section characteristics under non-oscillating conditions, with the screen (Grids #2 and #4) connected to the plate, the triode-connected characteristics are as follows:
| Parameter | Value |
|---|---|
| Plate Voltage | 12.6 V |
| Screen Voltage (Connected to Plate) | 12.6 V |
| Grid #3 Voltage | 0 V |
| Amplification Factor (between Grid #1 and Grids #2 & #4 connected to Plate) | 9.0 |
| Transconductance (between Grid #1 and Grids #2 & #4 connected to Plate) | 2400 µmhos |
| Cathode Current | 3.6 mA |
| Grid #1 Voltage for Plate Current (Ib) = 10 µA (approximate) | -3.3 V |
The direct interelectrode capacitances of the 12GA6 are specified both with and without an external shield. When a shield is used, it is an EIA 316 shield connected to Pin 2 (Cathode and Grid Number 5).
| Capacitance Parameter | With Shield | Without Shield | Unit |
|---|---|---|---|
| Grid #3 to All | 8.0 | 8.0 | µµF |
| Plate to All | 13 | 8.0 | µµF |
| Grid #1 to All | 5.0 | 5.0 | µµF |
| Cathode to All except Grid #1 | 20 | 15 | µµF |
| Grid #3 to Plate (Maximum) | 0.25 | 0.3 | µµF |
| Grid #1 to Grid #3 (Maximum) | 0.15 | 0.15 | µµF |
| Grid #1 to Plate (Maximum) | 0.05 | 0.1 | µµF |
| Grid #1 to Cathode | 2.5 | 2.5 | µµF |
The 12GA6 is a specialized miniature heptode designed for low-voltage pentagrid converter applications in automotive receivers. Operating directly from a 12-volt storage battery, it eliminates the need for high-voltage power generation. With a 12.6 V, 0.15 A heater, a maximum plate and screen rating of 16 V, and a conversion transconductance of 140 µmhos, the 12GA6 provides a compact, efficient solution for combined mixer and oscillator functions in mobile environments.
Miniature 7-contact
General specifications
Properties common to every published source and operating point.
Electrical assignments shared by every tube using this base designation.
| Terminal | Section | Connection | Evidence |
|---|---|---|---|
| PIN1G1 | A | G1 — Control Grid Chart transcription; independent manufacturer verification pending | Unverified EIA Base Connections, printed page 128, 7CH |
| PIN2G5 | A | G5 — Fifth GridGroup 7CH2 Chart transcription; independent manufacturer verification pending | Unverified EIA Base Connections, printed page 128, 7CH |
| PIN2K | A | K — CathodeGroup 7CH2 Chart transcription; independent manufacturer verification pending | Unverified EIA Base Connections, printed page 128, 7CH |
| PIN3H | — | H — Heater Chart transcription; independent manufacturer verification pending | Unverified EIA Base Connections, printed page 128, 7CH |
| PIN4H | — | H — Heater Chart transcription; independent manufacturer verification pending | Unverified EIA Base Connections, printed page 128, 7CH |
| PIN5P | A | P — Plate (Anode) Chart transcription; independent manufacturer verification pending | Unverified EIA Base Connections, printed page 128, 7CH |
| PIN6G2 | A | G2 — Screen GridGroup 7CH6 Chart transcription; independent manufacturer verification pending | Unverified EIA Base Connections, printed page 128, 7CH |
| PIN6G4 | A | G4 — Fourth GridGroup 7CH6 Chart transcription; independent manufacturer verification pending | Unverified EIA Base Connections, printed page 128, 7CH |
| PIN7G3 | A | G3 — Suppressor Grid Chart transcription; independent manufacturer verification pending | Unverified EIA Base Connections, printed page 128, 7CH |
1 physical section, each with unique specifications.
Section 1
Low-voltage heptode converter; promoted gm is conversion transconductance.
Source-dependent data
Each block preserves the test conditions and published values from one reference. Values from different sources are intentionally kept separate.
Data set 01
Published operating points and test conditions from this source.
Heater voltage
12.6 V
Heater current
150 mA
Conversion transconductance
140 uS
Converter
Oscillator transconductance
2400 uS
NotOscillating
Grid-to-plate capacitance
0.1 pF
Data set 02
Published operating points and test conditions from this source.
Plate voltage
12.6 V
Converter
Screen voltage
12.6 V
Converter
Grid #3 resistor
2.2 megohm
Converter
Grid #1 voltage RMS
7.6 V
Converter
Grid #1 resistor
33000 ohm
Converter
Plate current
0.3 mA
Converter
Screen current
0.8 mA
Converter
Oscillator cathode current
3.6 mA
Oscillator
Plate resistance
1000000 ohm
Converter
Conversion transconductance
740 uS
Converter
Oscillator amplification factor
9
Oscillator
Oscillator transconductance
2400 uS
Oscillator
Grid #3 to all capacitance
8 pF
Plate to all capacitance
8 pF
Grid #1 to all capacitance
5 pF
Grid #3-to-plate capacitance
0.3 pF