12DV8 — Duplex-Diode Space-Charge-Grid Tetrode

The 12DV8 is a miniature duplex-diode, space-charge-grid tetrode designed for use in automobile receivers. It serves as a combined detector, automatic volume control (AVC) rectifier, and transistor driver. The tetrode section of the tube is specifically engineered to operate with its plate and space-charge-grid voltages supplied directly from a 12-volt storage battery, making it highly suitable for hybrid vacuum-tube/transistor automotive systems.

Physical Construction and Basing

The 12DV8 is constructed in a miniature T-6 1/2 glass envelope with an E9-1 small button 9-pin base. The tube features a coated unipotential cathode and can be mounted in any position.

Physical Dimensions

• Maximum Diameter: 7/8 inch
• Maximum Overall Length: 2 5/8 inches
• Maximum Seated Height: 2 3/8 inches

Terminal Connections

The 12DV8 uses the 9HR basing arrangement. The pin connections, viewed from the bottom of the base, are as follows:

The diodes share a cathode connection with an internal shield on Pin 8, which is separate from the tetrode cathode on Pin 2.

Heater Characteristics and Automotive Service

The heater of the 12DV8 is designed for operation from either an alternating current (AC) or direct current (DC) supply.

Automotive Voltage Variations

When operated in automotive service from a nominal 12-volt source, the heater voltage is subject to wide fluctuations. Under no circumstances should the heater voltage fall below 10.0 volts or exceed 15.9 volts. While these extreme variations can be tolerated for short periods, operating at or near these limits impacts the tube's performance and longevity:

• Low Heater Voltage: Results in a sacrifice in electrical performance.
• High Heater Voltage: Significantly reduces the life expectancy of the tube.

To maximize equipment reliability, improved supply-voltage regulation is highly recommended.

Maximum Ratings

The following limiting values are established under the Design-Maximum System. These ratings represent the limits at which satisfactory tube life can be expected under the worst probable operating conditions, including supply-voltage variations, component tolerances, and environmental changes.

Direct Interelectrode Capacitances

The direct interelectrode capacitances of the 12DV8 are measured without an external shield:

Typical Operating Conditions and Characteristics

The tetrode section of the 12DV8 is designed to operate at very low voltages, typically matching the 12.6 V heater supply.

Average Characteristics

At a standard operating point, the average characteristics of the tetrode and diode sections are:

• Plate Voltage: 12.6 V
• Space-Charge-Grid Voltage: 12.6 V
• Cathode Resistor: 18 Ω
• Control-Grid Resistor: 4.7 MΩ
• Amplification Factor (Control Grid to Plate): 7.6
• Plate Resistance (Approximate): 900 Ω
• Transconductance (Control Grid to Plate): 8,500 µmhos
• Plate Current: 9.0 mA
• Space-Charge-Grid Current: 53 mA
• Average Diode Current (Each Diode, with 10 V DC applied): 3.0 mA

Class A Amplifier Operation

When configured as a Class A amplifier, the 12DV8 operates under the following typical conditions:

The low plate resistance of 900 ohms and high transconductance of 8,500 µmhos allow the tetrode section to efficiently drive a subsequent transistor stage, delivering a power output of 5 milliwatts into a 1,250-ohm load with low distortion.