10D2 — Double Diode Vacuum Tube

The 10D2 is an indirectly heated double diode vacuum tube featuring separate cathodes, designed specifically for series heater operation. It is housed in a compact glass envelope with a miniature seven-pin base. The tube is engineered for applications requiring two independent diode sections, such as detection, low-current rectification, or full-wave rectification circuits.

Heater and Electrical Ratings

The 10D2 is designed with an indirectly heated cathode configuration optimized for series-string heater loops. The heater operates at a nominal voltage of 19 V and a constant current of 0.1 A.

The absolute maximum ratings for each diode section and the heater-to-cathode insulation must be strictly observed to ensure reliable operation:

Physical Characteristics and Pinout

The 10D2 utilizes a clear glass bulb and a standard B7G miniature seven-pin base. The physical dimensions and weight of the device are as follows:

• Maximum Overall Length: 54 mm
• Maximum Seated Height: 47.5 mm
• Maximum Diameter: 19 mm
• Approximate Net Weight: 1/4 oz
• Approximate Packed Weight: 1/2 oz
• Mounting Position: Unrestricted

The B7G base pin connections, viewed from the free end of the pins, are configured as follows:

The inclusion of an internal shield connected to pin 6 helps minimize capacitive coupling between the two independent diode sections.

Inter-electrode Capacitances

The inter-electrode capacitances of the 10D2 are specified under two distinct measurement conditions, both utilizing a closely fitting metal can connected to earth:

1. Balanced-out Condition (): Inter-electrode capacitance measured with the external socket/holder capacitance balanced out.
2. Total Condition (†): Total capacitance including a Benjamin B7G ceramic holder (Type 75/833) and a cylindrical screen (Type 75/832). This specific holder incorporates a radial shield positioned between pins 1 and 7.

The capacitance values for both conditions are detailed below:

Note: The balanced-out capacitance between Cathode 1 and Heater (ck'-h) exhibits a minor variation between 2.27 pF and 2.47 pF across different production documentation issues.

Operating Characteristics and Curves

The electrical behavior of the 10D2 is characterized by its anode current response to applied anode voltage and its performance in full-wave rectification circuits.

Anode Current vs. Anode Voltage (Ia / Va)

The relationship between the anode current (Ia) and anode voltage (Va) for a single diode section is documented across two operating ranges:

• Low-Voltage Range: At very low anode potentials, conduction begins near -0.6 V. The anode current rises to approximately 0.5 mA at 0 V bias, 2.2 mA at 1.0 V, and reaches about 5.2 mA at 1.8 V.
• High-Voltage Range: When higher anode voltages are applied, the current increases significantly, reaching approximately 6 mA at 2 V, 27 mA at 6 V, and 53 mA at 10 V.

Full-Wave Rectification Regulation

When operated as a full-wave rectifier, the typical regulation performance is defined under the following circuit conditions:

• Limiting Resistance (Rlim): 300 ̩ per anode
• Filter Capacitance (C): 8 ̹F
• Supply Frequency (f): 50 c/s

Under these conditions, the direct current (D.C.) output voltage varies with the load current for three standard transformer secondary voltages:

• 150-0-150 V RMS Supply: The D.C. output voltage is approximately 210 V at 0 mA load, dropping smoothly to about 185 V at a full load of 20 mA.
• 100-0-100 V RMS Supply: The D.C. output voltage starts at approximately 140 V at 0 mA load and decreases to about 115 V at 20 mA.
• 50-0-50 V RMS Supply: The D.C. output voltage begins at approximately 70 V at 0 mA load and drops to about 50 V at 20 mA.

Technical Summary

The 10D2 is a versatile, indirectly heated double diode featuring separate cathodes and an internal shield, designed for series-string heater operation at 19 V, 0.1 A. Housed in a clear glass B7G miniature envelope, it offers unrestricted mounting flexibility and a compact physical profile. With a maximum peak inverse voltage rating of 500 V and a peak anode current capability of 50 mA per section, the 10D2 is well-suited for low-current power supplies, full-wave rectification, and signal detection. Its low inter-electrode capacitances—particularly the extremely low anode-to-anode and cathode-to-cathode values—ensure excellent isolation between the two diode sections when operated with appropriate shielding.