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Voltage Pentode - Sharp Cutoff (single) ·Pentode

12DK6

Sharp-cutoff miniature pentode designed as an IF amplifier in color and black-and-white television receivers. Its fixed-gain high-frequency characteristics suit television intermediate-frequency signal stages.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 1
Base: -
Socket code: B7G
Base pins: 7
Nominal heater: 12.6 V / 150 mA

Description

12DK6 — Sharp-Cutoff Pentode

The 12DK6 is a miniature, sharp-cutoff pentode designed primarily for use as an intermediate-frequency (IF) amplifier in both color and black-and-white television receivers. It belongs to a family of closely related tubes—including the 3DK6, 4DK6, and 6DK6—that share identical physical construction, electrode structures, and electrical characteristics, differing only in their heater ratings and specific heater-cathode voltage limits.

Physical Construction and Basing

The 12DK6 is constructed in a miniature T-5 1/2 glass envelope. It features a standard button 7-pin base (designated E7-1) and utilizes the 7CM basing arrangement. The physical dimensions of the tube are as follows:

Dimension	Value
Maximum Diameter	0.750 in.
Maximum Seated Height	1.875 in.
Maximum Overall Height	2.125 in.

The tube requires a standard miniature 7-contact socket. The internal electrode structure includes a suppressor grid (Grid No. 3) and an internal shield, which are designed to be connected directly to the cathode at the socket to ensure stable high-frequency operation.

Heater Specifications and Heater-Cathode Ratings

The 12DK6 is specifically designed for operation in circuits where a 12.6-volt heater supply is utilized, such as series-string heater chains. Its heater characteristics and heater-cathode voltage limits are distinct from other members of its tube family:

Parameter	12DK6	6DK6	4DK6	3DK6
Heater Voltage (AC/DC)	12.6 V	6.3 V	4.2 V	3.15 V
Heater Current	0.15 A (150 mA)	0.3 A (300 mA)	0.45 A (450 mA)	0.6 A (600 mA)
Average Warm-up Time	—	—	11 s	11 s

Heater-Cathode Voltage Limits

The insulation between the heater and the cathode is rated to withstand specific voltage potentials, which vary depending on the polarity and the nature of the voltage:

Heater Negative with Respect to Cathode:
- Peak Value: 200 V maximum.
- Total DC and Plate: 200 V maximum.
Heater Positive with Respect to Cathode:
- DC Component: 100 V maximum.
- Total DC and Peak: 200 V maximum.
- Average Value: 100 V maximum.

Electrical Characteristics and Class A1 Operation

Under typical Class A1 amplifier operating conditions, the 12DK6 exhibits high transconductance and a high plate resistance, making it highly effective for voltage amplification at intermediate frequencies. The typical operating parameters are defined as follows:

Parameter	Value
Plate Voltage	125 V
Grid No. 3 (Suppressor Grid) Voltage	Connected to cathode at socket
Grid No. 2 (Screen Grid) Voltage	125 V
Cathode-Bias Resistor	56 Ω
Plate Resistance (Approximate)	0.35 MΩ
Transconductance	9,800 µmhos
Plate Current	12.0 mA
Grid No. 2 Current	3.8 mA
Grid No. 1 Bias for Plate Current of 20 µA (Approximate)	−6.5 V

The low value of the cathode-bias resistor (56 ohms) combined with the relatively high plate current (12.0 mA) and screen current (3.8 mA) establishes a stable operating point that maximizes transconductance while maintaining the sharp-cutoff characteristic.

Maximum Ratings

The maximum ratings for the 12DK6 are established under the Design-Maximum Rating System. Operating the tube beyond these limits may compromise its performance and longevity.

Plate Voltage: 330 V maximum
Grid No. 3 (Suppressor Grid) Positive Voltage: 0 V maximum
Grid No. 2 (Screen Grid) Supply Voltage: 330 V maximum
Grid No. 2 Voltage: Subject to specific rating curves based on dissipation limits
Positive Grid No. 1 (Control Grid) Voltage: 0 V maximum
Plate Dissipation: 2.3 W maximum
Grid No. 2 Dissipation:
- For Grid No. 2 voltages up to 165 V: 0.55 W to 0.66 W maximum
- For Grid No. 2 voltages between 165 V and 330 V: Subject to specific rating curves

Direct Interelectrode Capacitances

Because the 12DK6 is designed for high-frequency IF amplifier service, minimizing feedback capacitance between the plate and the control grid is critical. The unshielded direct interelectrode capacitances are:

Grid No. 1 to Plate (Maximum): 0.025 pF
Input (Grid No. 1 to Cathode, Heater, Grid No. 2, Grid No. 3, and Internal Shield): 6.3 pF
Output (Plate to Cathode, Heater, Grid No. 2, Grid No. 3, and Internal Shield): 1.9 pF

These low capacitance values, particularly the extremely low grid-to-plate feedback capacitance of 0.025 pF maximum, allow for high-gain amplification stages without a high risk of regenerative feedback or oscillation.

Technical Summary

The 12DK6 is a miniature, sharp-cutoff pentode featuring a 7-pin button base and a T-5 1/2 envelope. It is designed for intermediate-frequency amplifier service in television receivers. Operating with a 12.6 V, 0.15 A heater, it is electrically identical to the 3DK6, 4DK6, and 6DK6 except for its heater ratings. Under typical Class A1 conditions with a plate and screen supply of 125 V, the tube provides a transconductance of 9,800 µmhos, a plate current of 12.0 mA, and an approximate plate resistance of 0.35 MΩ. Its design-maximum ratings include a maximum plate voltage of 330 V and a maximum plate dissipation of 2.3 W, making it a robust and high-performing choice for television IF stages.

Socket description

Miniature 7-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: -
Socket code: B7G
Base pins: 7
Nominal heater voltage: 12.6 V
Nominal heater current: 150 mA
Parallel heater voltage: -
Parallel heater current: -
Series capable: No

Terminal pinout

Electrical assignments shared by every tube using this base designation.

No verified pinout is recorded for this base designation.

Section ratings

1 physical section, each with unique specifications.

Section 1

Pentode

X-ray radiationInterelectrode capacitances

Plate resistance: 350000 Ω
Transconductance: 0.0098 S
Max plate voltage: 330 V
Max screen voltage: 330 V
Max plate dissipation: 2.3 W

Promoted from published maximum-ratings/characteristics tables; additional source values are retained in TUBE_SECTION_PARAMETER.

Source-dependent data

Operating conditions by source

Each block preserves the test conditions and published values from one reference. Values from different sources are intentionally kept separate.

Data set 01

1975 RCA RC30

Published operating points and test conditions from this source.

SECTION 1

Pentode

Other

Plate Current
15 mA
Published in approved 12DK6 target entry; Section1
Equivalent Noise Resistance
300 Ω
Published in approved 12DK6 target entry; Section1
Grid-Circuit Resistance
1 MΩ
Published in approved 12DK6 target entry; Section1
Heater to Cathode Circuit Resistance
0.02 MΩ
Published in approved 12DK6 target entry; Section1
Heater Voltage (ac/dc) 3.16 4.2 6.3
12.6 V
Published in approved 12DK6 target entry; Section1
Heater Current 0.6 0.45 0.3
150 mA
Published in approved 12DK6 target entry; Section1
Plate Voltage
330 V
Published in approved 12DK6 target entry; Section1
Grid-No.3 (Suppressor-Grid) Voltage, Positive value
0 V
Published in approved 12DK6 target entry; Section1
Grid-No.2 (Screen-Grid) Supply Voltage
330 V
Published in approved 12DK6 target entry; Section1
Grid-No.l (Control-Grid) Voltage, Positive-bias value
0 V
Published in approved 12DK6 target entry; Section1
Plate Dissipation
2.3 W
Published in approved 12DK6 target entry; Section1
For grid-No.2 voltages up to
165 V
Published in approved 12DK6 target entry; Section1
For grid-No.2 voltages up to 165 volts
0.55 W
Published in approved 12DK6 target entry; Section1
For grid-No.2 voltages between 165 and
330 V
Published in approved 12DK6 target entry; Section1

Capacitance

Internal Shield
6.3 pF
Published in approved 12DK6 target entry; Section1
Internal Shield
1.9 pF
Published in approved 12DK6 target entry; Section1

Characteristic

Grid-No.! Voltagre (Approx.) for plate current of 20 fiA
-6.5 V
Published in approved 12DK6 target entry; Section1