Voltage Radio Detector Converter ·Heptode
Heptode frequency changer for superheterodyne radio receivers, combining oscillator and mixer action within one multi-grid valve. Manufacturer data specify its conversion characteristics and operating conditions for dedicated receiver frequency-changing service.
An indirectly heated heptode vacuum tube designed primarily for use as a frequency changer in radio receivers. It features an English base configuration and is characterized by its low-voltage, high-current heater compared to its close relatives in the same family.
The 15A2 belongs to a family of heptode frequency changers that also includes the 15D1 and 15D2. While these three tubes share identical internal electrode structures and electrical operating characteristics, they are distinguished by their heater ratings to accommodate different receiver power supply designs.
The 15A2 is designed for a 4.0 V heater supply, making it suitable for standard AC-operated receivers. In contrast, the 15D1 and 15D2 are designed for 13.0 V operation, with heater currents of 0.2 A and 0.15 A respectively, typically used in series-string or mobile applications.
The electrical characteristics of the 15A2 family are equivalent to the widely documented 6A8G (also referred to in some historical references as the 6ABG).
The 15A2 is constructed in a glass envelope with a maximum diameter of 1-9/16 inches and a maximum overall height of 3-7/8 inches. It utilizes a standard 7-pin English base along with a top cap connector for the control grid. This physical arrangement ensures isolation of the sensitive input grid from the other electrodes, minimizing unwanted coupling and frequency drift in frequency conversion stages.
The pin connections, viewed from the bottom of the English base, are assigned as follows:
| Pin / Terminal | Electrode Connection |
|---|---|
| Pin 1 | Oscillator Grid (G1) |
| Pin 2 | Oscillator Anode (G2) |
| Pin 3 | Screen Grid (G3, G5) |
| Pin 4 | Heater (H) |
| Pin 5 | Heater (H) |
| Pin 6 | Cathode (K) |
| Pin 7 | Anode (A) |
| Top Cap | Control Grid (G4) |
The 15A2 operates as a pentagrid converter (heptode), where the first two grids (G1 and G2) function as the grid and anode of an oscillator, while the fourth grid (G4) acts as the control grid for the incoming radio frequency (RF) signal. Grids 3 and 5 (G3, G5) are internally connected to act as a screen grid, shielding the control grid from the oscillator and anode sections.
When operated as a frequency changer, the typical electrical parameters for the 15A2 are defined at the following operating point:
These parameters demonstrate that the tube achieves a conversion conductance of 0.55 mA/V under standard operating conditions, providing efficient frequency translation with a high anode impedance of 360,000 ohms to maintain excellent selectivity in the subsequent intermediate frequency (IF) stages.
The 15A2 is an English-base heptode frequency changer featuring a 4.0 V, 0.65 A heater. It is electrically identical to the 13.0 V types 15D1 and 15D2, and shares its electrical characteristics and curves with the 6A8G (or 6ABG). With its specialized seven-electrode structure, including a top-cap control grid (G4), it provides stable oscillator and mixer performance in superheterodyne receivers, delivering a conversion conductance of 0.55 mA/V at an anode voltage of 250 V.
International Octal
General specifications
Properties common to every published source and operating point.
Electrical assignments shared by every tube using this base designation.
No verified pinout is recorded for this base designation.
1 physical section, each with unique specifications.
Section 1
Brimar 15A2 heptode frequency changer, English octal base; 4.0 V 0.65 A heater. Typical converter circuit: anode 250 V at 3.5 mA, screen grids G3/G5 100 V at 2.7 mA, oscillator anode G2 200 V at 4.0 mA, mixer control G4 -3 V, oscillator grid G1 resistor 50 kΩ, oscillator grid current 0.4 mA. Conversion conductance 0.55 mA/V is conversion gain characteristic, not intrinsic static transconductance; anode resistance ~360 kΩ already recorded. Brimar refers to 6A8G for further characteristics; operating voltages do not establish unrestricted maxima.
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.
Anode Voltage
250 V
Anode Current
3.5 mA
Screen Voltage
100 V
G3,G5
Screen Current
2.7 mA
Oscillator Anode Voltage
200 V
G2
Oscillator Anode Current
4 mA
Control Grid Voltage
-3 V
G4
Oscillator Grid Resistor
50000 ohm
G1
Oscillator Grid Current
0.4 mA
Conversion Conductance
550 uS