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Power - Beam Single (NOT sweep) (under 10W) ·BeamPower

12A6GT

Glass tubular beam-power output tube for Class-A audio-frequency amplification in radio and related receiving equipment, using a 12.6 V heater.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
-
Socket code
IO
Base pins
7
Nominal heater
12.6 V / 150 mA

Description

12A6GT — Beam Power Amplifier

The 12A6GT is an indirectly heated beam power amplifier designed for audio-frequency power amplification. It features a unipotential cathode and is housed in a glass envelope, offering efficient power output in Class A1 amplifier applications.

Physical Specifications and Basing

The 12A6GT is constructed with a T-9 glass bulb and an intermediate shell octal base. Although octal bases typically accommodate eight pins, this tube uses a 7-pin configuration where Pin 6 is omitted. The tube does not have a top cap.

The physical dimensions of the tube are:

  • Maximum Diameter: 1 5/16 inches
  • Maximum Overall Length: 3 1/4 inches
  • Maximum Seated Height: 2 11/16 inches

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

Pin NumberConnection
Pin 1No Connection
Pin 2Heater
Pin 3Plate
Pin 4Grid 2 (Screen Grid)
Pin 5Grid 1 (Control Grid)
Pin 6None (Omitted Pin)
Pin 7Heater
Pin 8Cathode & Deflector

The tube operates with its unipotential cathode and deflector connected together at Pin 8.

Heater and Interelectrode Capacitances

The 12A6GT features a heater designed for operation in circuits providing a nominal 12.6 V.

  • Heater Voltage: 12.6 V
  • Heater Current: 0.15 A
  • Calculated Heater Power: 1.89 W (calculated as 12.6 V × 0.15 A)

When measured with a standard RMA shield (type M8-308), the direct interelectrode capacitances of the tube are:

  • Control Grid to Cathode: 9.0 µµF
  • Plate to Cathode: 9.0 µµF
  • Grid to Plate: 0.6 µµF (Maximum)

Maximum Ratings

The maximum ratings for the 12A6GT are established in accordance with the RMA Standard M8-210. These ratings represent the limiting values of operating and environmental conditions for the tube:

Rating ParameterMaximum Value
Maximum Plate Voltage250 V
Maximum Screen (Grid 2) Voltage250 V
Maximum Plate Dissipation7.5 W
Maximum Screen (Grid 2) Dissipation1.5 W

Typical Operating Conditions and Characteristics

In typical Class A1 audio-frequency amplifier service, the 12A6GT operates with equal plate and screen voltages. The typical operating parameters are defined as follows:

  • Heater Voltage: 12.6 V
  • Heater Current: 0.15 A
  • Plate Voltage: 250 V
  • Screen Voltage: 250 V
  • Control Grid (Grid 1) Voltage: -12.5 V
  • Peak AF Signal Voltage: 12.5 V
  • Zero-Signal Plate Current: 30 mA
  • Maximum-Signal Plate Current: 32 mA
  • Zero-Signal Screen Current: 3.5 mA
  • Maximum-Signal Screen Current: 5.5 mA
  • Transconductance: 3000 µmhos
  • Load Resistance: 7500 Ω
  • Total Harmonic Distortion: 7%
  • Power Output: 3.0 W

The plate resistance and amplification factor are not specified for these typical operating conditions.

Grid Circuit Resistance Limits

To ensure stable operation and prevent thermal runaway or bias instability under maximum rated conditions, limits are placed on the direct current (DC) resistance in the control grid circuit:

  • Self-Bias Operation: The DC resistance in the grid circuit must not exceed 0.5 Megohm.
  • Fixed Bias Operation: The DC resistance in the grid circuit must not exceed 0.1 Megohm.

Socket description

International Octal

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
-
Socket code
IO
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

Beam Power

X-ray radiationInterelectrode capacitances
Transconductance
0.003 S
Max plate voltage
250 V
Max screen voltage
250 V
Max plate dissipation
7.5 W
Max screen dissipation
1.5 W

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

1961 Tung Sol

Published operating points and test conditions from this source.

SECTION 1

Beam Power

Capacitance

  • Control Grid to Cathode

    9 pF

  • Plate to Cathode

    9 pF

  • Grid to Plate

    0.6 pF

Other

  • Heater Or Filament Voltage

    12.6 V

  • Max Imum Plate Voltage

    250 V

  • Max Imum Screen Voltage

    2 V

  • Maximum Plate Dissipation

    7.5 W

  • Max Imum Screen Dissipation

    1.5 W

Characteristic

  • Plate Voltage

    250 V

  • Screen Voltage

    250 V

  • Control Gr1Id Voltage

    -12.5 V

  • Peak Af Signal Voltage

    12.5 V

  • Zero—Signal Plate Current

    30 mA

  • Zero—Signal Screen Current

    3.5 mA

  • Max Imum=—S| Gnal Plate Current

    3 mA

  • Transconductance

    3000 uS

  • Load Resistance

    7500 ohm

  • Power Output

    3 W