12BH7AEH — Miniature Twin Triode Vacuum Tube

The 12BH7AEH (also designated as 12BH7AEH gold) is a miniature twin triode vacuum tube featuring equipotential (indirectly heated) cathodes. It is designed specifically to amplify low-frequency voltage in radio engineering devices. The tube features two independent triode sections housed within a single miniature glass envelope, sharing a versatile heater arrangement that supports both series and parallel filament connections.

Physical Construction and Pin Configuration

The 12BH7AEH is constructed in a miniature glass envelope with a maximum overall height of 56.5 mm and a bulb diameter of 22.5 mm (with a tolerance of -2 mm, giving a range of 20.5 mm to 22.5 mm).

The tube utilizes a 9-pin base arrangement. The pins are spaced at 36° intervals (8 × 36° = 288° total angle), with a pin circle diameter of 12 mm. Each pin has a nominal diameter of 1 mm (with a tolerance of +0.03 mm to -0.07 mm).

The electrode-to-lead connections are assigned as follows:

The heater is tapped, allowing for either series or parallel connection using pins 4, 5, and 9.

Heater and Filament Ratings

The 12BH7AEH heater can be operated in either parallel or series configurations, depending on the supply voltage:

• Parallel Connection: Nominal filament voltage is 6.3 V (permissible range of 6.0 V to 6.6 V). Under this condition, the heater current is rated between 550 mA and 680 mA.
• Series Connection: Nominal filament voltage is 12.6 V (permissible range of 12.0 V to 13.2 V). Under this condition, the heater current is rated between 275 mA and 340 mA.

The cathode-to-heater insulation is rated to withstand a maximum voltage of ±200 V, with a minimum insulation resistance of 10 MΩ under these conditions.

Electrical Characteristics and Operating Parameters

The electrical parameters of each triode section are measured under specific nominal test conditions: a plate voltage of 250 V, a negative grid bias of -10.5 V, and a filament voltage of either 6.3 V or 12.6 V. Under these conditions, the tube exhibits the following characteristics:

• Plate Current ($I_p$): Nominal range of 9.0 mA to 16.0 mA.
• Plate Current Balance: The difference in plate current between the first and second triode sections is restricted to a maximum of ±30%.
• Slope of Characteristic (Transconductance, $g_m$): Rated between 2.4 mA/V and 4.0 mA/V (equivalent to 2,400 to 4,000 µmhos).
• Amplification Factor ($\mu$): Minimum of 14 (no maximum specified).
• Grid Reverse Current: Maximum of 0.2 µA when tested with a grid circuit resistance of 0.25 MΩ.
• Cutoff Characteristics: At a plate voltage of 250 V and an increased negative grid bias of -23.0 V, the plate current at the beginning of the characteristic is limited to a maximum of 80 µA.

Maximum Permissible Operating Conditions

To ensure reliable operation and prevent damage, circuit designs must respect the following absolute maximum ratings for each triode section:

The maximum plate dissipation of 3.5 W applies to each triode section individually. The grid circuit resistance limits differ significantly depending on the biasing method, with self-bias allowing up to 1.0 MΩ compared to the more stringent 0.25 MΩ limit for fixed-bias configurations.

Characteristic Curves and Behavior

The electrical behavior of the 12BH7AEH is illustrated by two primary sets of characteristic curves:

1. Plate Current vs. Grid Voltage ($I_p = f(E_g)$): These transfer curves, plotted at a filament voltage of 6.3 V, show the relationship between plate current and grid voltage for plate voltages of 200 V, 250 V, and 300 V. The curves demonstrate that at a plate voltage of 250 V, the plate current approaches zero (cutoff) near a grid voltage of -23 V, matching the tabulated cutoff specification of 80 µA maximum. As the grid voltage becomes less negative, the plate current rises steeply, illustrating the transconductance (slope) of the device.

2. Plate Current vs. Plate Voltage ($I_p = f(E_p)$): These plate curves, also plotted at a filament voltage of 6.3 V, display plate current (up to 80 mA) against plate voltage (up to 300 V) for discrete grid bias steps ranging from 0 V down to -18 V (specifically including curves for $E_g = 0\text{ V}, -4\text{ V}, -6\text{ V}, -8\text{ V}, -10.5\text{ V}, -12\text{ V}, -14\text{ V}, \text{ and } -18\text{ V}$). These curves show the triode's low plate resistance and its ability to handle relatively high peak currents under dynamic conditions, while remaining within the continuous average cathode current limit of 20 mA and plate dissipation limit of 3.5 W.

Technical Summary

The 12BH7AEH and 12BH7AEH gold are high-performance, miniature twin triodes designed for low-frequency voltage amplification in radio engineering applications. Featuring independent, equipotential cathodes and a flexible heater design (supporting 6.3 V / 550–680 mA parallel or 12.6 V / 275–340 mA series operation), the tube is well-suited for a variety of audio and instrumentation circuits. With a maximum plate voltage of 300 V, a maximum plate dissipation of 3.5 W per section, and a nominal transconductance of 2.4 to 4.0 mA/V, it provides robust voltage amplification with moderate power-handling capabilities in a compact 9-pin miniature package.