1A2P — Miniature Frequency-Conversion Heptode

The 1A2P (also designated as 1А2П) is a miniature, directly heated heptode designed primarily for frequency conversion applications in radio receivers. Featuring an oxide-coated filamentary cathode, this glass-envelope tube is engineered for low power consumption and reliable operation under varied environmental conditions.

Construction, Filament, and Base Pinout

The 1A2P is housed in a miniature glass envelope with a maximum mass of 10 grams. It features a maximum diameter of 19.2 mm, a body height of 40 ± 2.5 mm, and a maximum overall height of 57 mm including the pins. The tube utilizes a 7-pin miniature base (compatible with the RSH4 socket type) and can be operated in any mounting position.

The filament is directly heated and oxide-coated, designed for low-voltage battery operation. The filament ratings and connections are as follows:

The 7-pin base configuration provides the following connections:

• Pin 1: Cathode (negative filament terminal) and Grid 5
• Pin 2: Anode
• Pin 3: Grid 2 and Grid 4
• Pin 4: Grid 1
• Pin 5: Cathode (negative filament terminal) and Grid 5
• Pin 6: Grid 3
• Pin 7: Cathode (positive filament terminal)

In this heptode structure, Grid 5 is internally tied to the negative side of the filamentary cathode (Pins 1 and 5), while Grid 2 and Grid 4 are internally connected to each other and brought out to Pin 3.

Electrical Characteristics and Operating Points

The typical electrical parameters of the 1A2P are specified under the following test conditions: a filament voltage ($U_f$) of 1.2 V, an anode voltage ($U_a$) of 60 V, screen grid voltages ($U_{[g2](/tubes/G2),g4}$) of 45 V, a control grid voltage ($U_{g3}$) of 0 V, and an RMS oscillator grid voltage ($U_{g1\_rms}$) of 8 V. Under these conditions, the typical parameters are:

• Anode Current ($I_a$): 0.7 ± 0.3 mA
• Screen Grid Current ($I_{[g2](/tubes/G2)} + I_{g4}$): 1.1 ± 0.5 mA
• Grid 1 Current ($I_{g1}$): 115 µA (with a -35 µA tolerance, i.e., 80 to 115 µA)
• Grid 1 Leak Resistance: 51 kΩ
• Conversion Transconductance ($S_c$): 0.24 mA/V (with a -0.07 mA/V tolerance, i.e., 0.17 to 0.24 mA/V) at an alternating $U_{g3}$ of 0.7 $V_{rms}$
• Heterodyne Oscillator Transconductance ($S_{het}$): 0.82 mA/V (with a -0.17 mA/V tolerance, i.e., 0.65 to 0.82 mA/V) measured at an anode voltage of 45 V
• Inverse Grid 3 Current ($I_{g3\_inv}$): ≤ 0.3 µA at a grid bias of $U_{g3} = -1$ V
• End-of-Life Conversion Transconductance: ≥ 0.1 mA/V after 1500 operating hours

Maximum Ratings and Environmental Limits

To ensure reliable operation and prevent premature degradation, the operating conditions of the 1A2P must be kept within the following absolute limit values:

Service and Environmental Conditions

The tube is designed to withstand mechanical and environmental stress, making it suitable for portable or ruggedized equipment:

• Vibration Resistance: Capable of withstanding continuous vibration at 50 Hz with an acceleration of up to 2.5 g.
• Ambient Temperature Range: -45 °C to +70 °C.
• Relative Humidity: Up to 98% at temperatures up to 25 °C.

Interelectrode Capacitances

The interelectrode capacitances of the 1A2P heptode are characterized as follows:

• Input Capacitance: 5.1 pF
• Output Capacitance: 6.3 pF
• Transfer Capacitance: ≤ 0.6 pF
• Heterodyne Oscillator Input Capacitance: 0.95 pF
• Heterodyne Oscillator Output Capacitance: 7.3 pF
• Grid 1 to Grid 3 Capacitance: 0.14 pF
• Grid 1 Leak Capacitance: $4 \times 10^{-6}$ pF

Characteristic Curves and Behavior

The physical behavior of the 1A2P is characterized by several key non-linear relationships:

• Filament Voltage Effects: Both the filament current and the heterodyne oscillator transconductance rise non-linearly as the filament voltage ($U_f$) is increased from 0.2 V to 1.6 V.
• Anode Voltage Saturation: The anode current and the combined screen grid (Grid 2 and Grid 4) current exhibit saturation behavior as the anode voltage ($U_a$) increases beyond 20 V. This saturation is observed across various Grid 1 bias voltages.
• Heterodyne Oscillator Triode Behavior: When Grids 2 and 4 are connected directly to the anode to operate the structure as a triode oscillator, the heterodyne anode characteristics show typical triode-like behavior. Under these conditions, the anode current can reach up to 6 mA at a combined anode and screen voltage ($U_{a,[g2](/tubes/G2),g4}$) of 220 V with a Grid 1 bias ($U_{g1}$) of -4 V.

Technical Summary

The 1A2P is a miniature, directly heated heptode designed for frequency conversion in battery-powered and portable radio equipment. Operating with a nominal filament supply of 1.2 V at 30 mA, it provides a conversion transconductance of 0.24 mA/V and a heterodyne oscillator transconductance of 0.82 mA/V under typical operating conditions. With its robust mechanical ratings, including vibration resistance up to 2.5 g and a wide operating temperature range from -45 °C to +70 °C, the 1A2P offers reliable performance in a compact 10-gram glass envelope.