Voltage Radio Detector Converter ·Heptode
12A8G
Heptode converter for superheterodyne receivers, combining local-oscillator and mixer action in one multi-grid structure. Its series-heater characteristics make it well suited to AC/DC radio receiver designs.
- Sections
- 1
- Base
- 8-A
- Socket code
- IO
- Base pins
- 8
- Nominal heater
- 12.6 V / 150 mA
Description
12A8G — Heptode Frequency Converter
The 12A8G is an indirectly heated heptode frequency converter designed for superheterodyne radio receiver applications. It combines mixer and oscillator functions within a single glass envelope. The tube features a 12.6 V heater, an ST-12 glass bulb, a standard 8-pin octal base, and a miniature top cap.
Mechanical Construction and Basing
The 12A8G is constructed with an ST-12 (or ST-12C) glass envelope. It utilizes an 8-pin octal shell base (designated as 8-A) and a miniature top cap for the control grid connection.
The physical dimensions of the tube are:
- Maximum overall length: 4-15/32 inches
- Maximum seated height: 3-29/32 inches
- Maximum diameter: 1-9/16 inches
Pinout Configuration
The basing arrangement (8A, viewed from the bottom) provides the following connections:
- Pin 1: No Connection (or Shield/Ground connection in some configurations)
- Pin 2: Heater
- Pin 3: Plate
- Pin 4: Screen (Grids 3 and 5, designated as G3 + G5)
- Pin 5: Oscillator Grid (Grid 1, designated as G1)
- Pin 6: Anode-Grid (Grid 2, designated as G2)
- Pin 7: Heater
- Pin 8: Cathode (or Cathode and Grid 4, designated as K + G4)
- Top Cap: Control Grid (Grid 4, designated as G or G4)
Heater and Electrical Ratings
The 12A8G is designed for series or parallel heater operation, requiring a nominal heater voltage of 12.6 volts and drawing a current of 0.150 amperes (150 mA).
Maximum Ratings
The absolute maximum electrical limits for the 12A8G are:
- Plate Voltage: 250 max. volts
- Screen Voltage (Grids 3 and 5): 100 max. volts
- Anode-Grid Supply Voltage (Grid 2): 250 max. volts
Typical Operating Conditions and Characteristics
Under typical operating conditions as a frequency converter, the 12A8G operates with the following parameters:
- Control-Grid Voltage (Grid 4): -3 volts
- Anode-Grid Series Resistor: 20,000 ohms
- Oscillator Grid Resistor: 50,000 ohms
- Plate Current: 3.5 mA
- Screen Current: 2.7 mA
- Anode-Grid Current: 4 mA
- Oscillator-Grid Current (minimum recommended): 0.3 mA
- Conversion Conductance: 550 µmhos
- Plate Resistance: 0.36 MΩ (360,000 ohms)
- Grid Voltage for Conversion Cutoff: -35 volts (for a conversion conductance of 2 to 5 µmhos)
Interelectrode Capacitances
When measured with a form-fitting shield, the interelectrode capacitances of the 12A8G are:
| Capacitance Parameter | Value |
|---|---|
| Grid 4 to Plate | 0.26 µµF |
| Grid 4 to Grid 5 (or Grid 2) | 0.15 µµF |
| Grid 4 to Grid 1 | 0.15 to 0.16 µµF |
| Grid 1 to Grid 2 | 1.1 µµF |
| RF Input (Grid 4 to all other electrodes) | 9.5 µµF |
| Oscillator Output (Except Grid 1) | 4.5 µµF |
| Oscillator Input (Except Grid 2) | 6.0 µµF |
| Converter Output | 12.0 µµF |
Related Designations and Comparisons
The electrical characteristics and applications of the 12A8G are identical to those of the Sylvania type 6A8G, with the exception of its heater ratings and specific interelectrode capacitances. The 6A8G operates with a different heater supply, whereas the 12A8G is optimized for 12.6 V, 0.150 A operation.
Technical Summary
The 12A8G is an octal-based, indirectly heated heptode frequency converter featuring a 12.6 V / 0.150 A heater, an ST-12 glass envelope, and a top cap. It is designed to perform both oscillator and mixer functions in superheterodyne receivers. With a conversion conductance of 550 µmhos and a plate resistance of 0.36 MΩ under typical operating conditions, the 12A8G provides reliable frequency conversion.
Socket description
International Octal
General specifications
Tube and section characteristics
Properties common to every published source and operating point.
Heater and base
- Base
- 8-A
- 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
8-A - 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
- Plate resistance
- 600000 Ω
- Transconductance
- 0.0005 S
- Max plate voltage
- 250 V
- Max screen voltage
- 100 V
Promoted ratings/characteristics read from the approved National Union datasheet.
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.