12BV11 — Twin Dual-Control Sharp-Cutoff Pentode

The 12BV11 is a multi-electrode vacuum tube of the compactron family, designed primarily for use as a color demodulator in color television receivers. It contains two independent, sharp-cutoff pentode units within a single T-9 glass envelope. A key feature of its design is that both Grid No. 1 (control grid) and Grid No. 3 (suppressor grid) of each pentode section are designed to operate as independent control electrodes, allowing for dual-signal control or demodulation functions within each unit.

The 12BV11 is identical to the 6BV11 except for its heater ratings, with the 12BV11 configured for parallel heater circuits and the 6BV11 configured for series heater circuits.

Physical Construction and Basing

The 12BV11 is constructed in a compactron T-9 glass bulb with a button 12-pin base (E12-70 designation). This physical configuration requires a standard duodecar 12-contact socket.

The physical dimensions of the tube are:

• Maximum Diameter: 1.188 inches
• Maximum Seated Height: 2.250 inches
• Maximum Overall Height: 2.625 inches

Pinout Configuration (12HB Basing)

The tube utilizes the 12HB basing arrangement. An internal shield is incorporated within the structure to minimize crosstalk and unwanted coupling between the two pentode sections. This internal shield is internally connected to the heater at Pin 12. To achieve the specified electrical characteristics and ensure stable operation, Pin 12 must be connected directly to circuit ground.

The pin connections, viewed from the bottom of the tube base, are assigned as follows:

Heater Characteristics

The heater of the 12BV11 is designed for parallel operation in equipment with a nominal 12.6 V supply. It features a controlled warm-up time to ensure reliable operation in series-parallel or coordinated heater strings.

For comparison, the otherwise identical 6BV11 utilizes a series heater arrangement operating at 6.3 V with a current draw of 0.9 A (900 mA).

Direct Interelectrode Capacitances

The direct interelectrode capacitances of the 12BV11 are measured without an external shield. The values for each of the two pentode sections are symmetrical and are specified as follows:

The low capacitance between Grid No. 1 and Grid No. 3 (0.08 pF) is critical for preventing signal leakage and maintaining isolation between the two independent control inputs of each pentode section.

Electrical Characteristics and Typical Operation

Under typical Class A1 amplifier operating conditions, each pentode section of the 12BV11 exhibits the following characteristics. In this operating state, Grid No. 3 is maintained at a DC potential of 0 volts.

The dual-control nature of the tube is reflected in the transconductance figures: Grid No. 1 provides a high transconductance of 3200 µmhos for sensitive control, while Grid No. 3 provides a lower transconductance of 390 µmhos, suitable for injection of a local oscillator or reference signal in demodulator circuits.

Maximum Ratings and Circuit Values

The maximum ratings are established under the Design-Maximum Rating System. These limits must not be exceeded under the worst-case operating conditions of supply voltage variation, component tolerances, and signal modulation.

Maximum Ratings (Each Section)

Note: For Grid No. 2 voltages between 150 V and 300 V, the maximum Grid No. 2 input is restricted and must be determined in accordance with standard screen-grid rating curves.

Maximum Circuit Values

To prevent thermal runaway and ensure bias stability, the resistance in the grid circuits must be kept within the following limits:

• Grid No. 3 Circuit Resistance (Each Unit): 0.68 MΩ maximum.
• Grid No. 1 Circuit Resistance (Each Unit):
  • For fixed-bias operation: 0.22 MΩ maximum.
  • For cathode-bias (self-bias) operation: 0.47 MΩ maximum.

Technical Summary

The 12BV11 is a specialized compactron twin dual-control sharp-cutoff pentode designed for color television demodulator applications. Operating with a 12.6 V, 0.45 A parallel heater, it houses two independent pentode units in a single T-9 envelope. Each unit features independent control capabilities on both Grid No. 1 and Grid No. 3, with Grid No. 1 offering a transconductance of 3200 µmhos and Grid No. 3 offering 390 µmhos under typical operating conditions. The integration of an internal shield connected to the heater at Pin 12 provides the necessary isolation between sections, provided Pin 12 is tied directly to ground. With a maximum plate voltage rating of 300 V and a plate dissipation limit of 1.7 W per section, the 12BV11 provides a compact and efficient solution for dual-control signal processing and demodulation.