12GN6 — Remote-Cutoff Pentode and Demodulator Diode

The 12GN6 is a multi-unit miniature vacuum tube containing a high-gain, remote-cutoff pentode and a single demodulator diode sharing a common cathode. It is designed primarily for service in television and radio receivers as a high-gain radio-frequency (R.F.) or intermediate-frequency (I.F.) amplifier and demodulator.

Construction, Heater, and Pinout

The 12GN6 is constructed in a T-5 1/2 glass bulb utilizing a miniature button 7-pin base (basing designation 7FW). The tube features a coated unipotential cathode that is shared between the pentode and diode sections. It is designed to operate in any mounting position.

The physical dimensions of the T-5 1/2 envelope are:

• Maximum overall length: 2-1/4 inches
• Maximum seated height: 2 inches
• Maximum diameter: 3/4 inch

Heater Specifications

The heater is designed for either AC or DC operation. The nominal heater characteristics are:

• Heater Voltage: 12.6 V
• Heater Current: 0.15 A
• Calculated Heater Power: 1.89 W (calculated as $12.6\text{ V} \times 0.15\text{ A}$)

Pin Connections

The bottom view of the 7-pin base provides the following electrode connections:

Direct Interelectrode Capacitances

The interelectrode capacitances of the 12GN6 are specified both with and without an external shield. When an external shield is employed, it is connected to Pin 2 (which ties to the cathode, suppressor grid, and internal shield).

Maximum Ratings

The maximum ratings for the 12GN6 are established under the Design Center System. These limits represent the maximum values that the manufacturer recommends should not be exceeded under any normal operating conditions:

Typical Operating Conditions and Class A1 Characteristics

The pentode section of the 12GN6 is typically operated as a Class A1 amplifier. The suppressor grid (Grid No. 3) must be connected directly to the cathode at the socket (Pin 2). The manufacturer specifies two typical operating points:

Remote-Cutoff and Diode Performance

The remote-cutoff characteristic of the pentode section is demonstrated by the grid bias required to reduce transconductance. At both the 100 V and 250 V plate operating points, applying an approximate negative bias of $-20\text{ V}$ to Grid No. 1 reduces the transconductance ($g_m$) from its nominal values (4,300 or 4,400 µmhos) down to a very low level of $40\text{ }\mu\text{mhos}$. This wide cutoff range allows effective automatic gain control (AGC) in R.F. and I.F. stages without causing severe cross-modulation or distortion on strong signals.

The demodulator diode shares the common cathode with the pentode. Under typical operating conditions, the diode section exhibits an average diode current of 1.5 mA when a direct-current potential of 10 V D.C. is applied. The maximum continuous diode current rating is restricted to 1.0 mA under normal operation, ensuring long-term stability and preventing excessive emission wear on the shared cathode structure.

Related Designations

The 12GN6 is closely related to the 6GN6. Except for their heater characteristics (voltage, current, and warm-up time), the two tubes are identical in construction, ratings, and electrical characteristics. The 6GN6 is designed for 6.3 V heater circuits, whereas the 12GN6 is designed for 12.6 V heater circuits, making them non-interchangeable without circuit modifications to the heater supply.

Technical Summary

The 12GN6 is a 7-pin miniature, indirectly heated vacuum tube combining a remote-cutoff pentode and a demodulator diode on a common cathode. Operating with a 12.6 V, 0.15 A heater, it provides high-gain R.F. and I.F. amplification alongside demodulation capabilities in a single compact envelope. With a maximum plate rating of 300 V and a plate dissipation limit of 3.0 W, the pentode section delivers a transconductance of 4,300 to 4,400 µmhos under typical Class A1 conditions, while its remote-cutoff design allows for smooth automatic gain control.