Skip to main content
Tube Tinker — Electron Tube Database
Alternatives & variationsDownload PDF datasheet

Voltage Pentode - Remote Cutoff (single) ·Pentode

1AB5

Remote-cutoff RF pentode using a 1.2 V, 0.13 A filament. Designed for variable-gain radio-frequency amplification, its remote-cutoff characteristic makes it particularly suitable for controlled RF/IF stages in low-voltage equipment.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
8BR
Socket code
-
Base pins
8
Nominal heater
1.2 V / 130 mA

Description

1AB5 — Remote-Cutoff RF Pentode

The 1AB5 is a filamentary, remote-cutoff RF pentode designed primarily for use as a mixer or radio-frequency (RF) amplifier. It is particularly suited for applications requiring higher transconductance than the 1LN5. Featuring a coated filament designed for low-power DC operation, the 1AB5 is constructed in a compact glass envelope and is documented with both five-pin and eight-pin lock-in base configurations.

Mechanical Construction, Base, and Pinout

The 1AB5 is constructed with a T-9 glass bulb and can be operated in any mounting position. Its physical dimensions include a maximum overall length of 2-9/32 inches, a maximum seated height of 1-3/4 inches, and a maximum diameter of 1-3/16 inches.

The tube is documented with two distinct base and pinout configurations:

5BP Base Connection

In this configuration, the tube utilizes a 5-pin arrangement designated as 5BP:

  • Pin 1: Filament Negative (F-)
  • Pin 2: Plate (P)
  • Pin 3: Grid #2 (G2 / Screen Grid)
  • Pin 4: Grid #1 (G1 / Control Grid)
  • Pin 5: Filament Positive (F+)

5BF Lock-In Base Connection

Alternatively, the tube is available in an 8-pin lock-in construction designated as 5BF:

  • Pin 1: Filament Positive (F+)
  • Pin 2: Plate (P)
  • Pin 3: Grid #2 (G2 / Screen Grid)
  • Pin 4: No Connection (NC)
  • Pin 5: No Connection (NC)
  • Pin 6: Grid #1 (G1 / Control Grid)
  • Pin 7: Filament Negative (F-)
  • Pin 8: Filament Negative (F-)

Filament and Interelectrode Capacitances

The 1AB5 features a coated filament designed for battery-operated or low-power portable equipment.

Filament ParameterValue
Filament Voltage (DC)1.2 V
Filament Current0.130 A (130 mA)

Direct interelectrode capacitances are measured with an RMA Shield #308 connected to the negative filament terminal:

  • Grid to Plate (G1 to P): 0.25 pF (maximum)
  • Input (G1 to F + G2 + G3): 2.8 pF
  • Output (P to F + G2 + G3): 4.2 pF

Maximum Ratings

The maximum ratings for the 1AB5 are established under the RMA Standard MB-210 system:

Rating ParameterAbsolute Maximum
Plate Voltage150 V
Grid #2 (Screen) Voltage150 V
Positive DC Grid #1 Voltage0 V
Plate Dissipation1.0 W
Grid #2 Dissipation0.3 W

Typical Operating Conditions and Characteristics

The 1AB5 can be operated under Class A (or Class A1) amplifier conditions. Two typical operating points are documented, representing operation at 90 V and 150 V:

Parameter90 V Operating Point150 V Operating Point
Filament Voltage (DC)1.2 V1.2 V
Filament Current130 mA130 mA
Plate Voltage90 V150 V
Grid #2 (Screen) Voltage90 V150 V
Grid #1 (Control Grid) Voltage0 V-1.5 V
Grid #1 Resistor (Self Bias)1.0 MΩ170 Ω
Plate Current3.5 mA6.8 mA
Grid #2 Current0.8 mA2.0 mA
Plate Resistance (Approx.)275,000 Ω125,000 Ω
Transconductance1100 µmhos1350 µmhos

Remote-Cutoff Characteristics

As a remote-cutoff pentode, the transconductance of the 1AB5 decreases gradually as negative grid bias is increased. The control grid voltage required to reduce transconductance to specific levels is documented as follows:

  • At 90 V operation:
    • Grid #1 voltage for a transconductance of 725 µmhos: -3 V (approximate)
    • Grid #1 voltage for a transconductance of 10 µmhos: -14 V (approximate)
  • At 150 V operation:
    • Grid #1 voltage for a transconductance of 725 µmhos: -6 V (approximate)
    • Grid #1 voltage for a transconductance of 10 µmhos: -23 V (approximate)

Analysis of Characteristic Curves

The behavior of the 1AB5 across varying electrode potentials is illustrated by its characteristic curves:

  • Plate Characteristics (Ec2 = 150 V): The plate current curves flatten significantly once the plate voltage rises above approximately 50 V, demonstrating the high plate resistance characteristic of a pentode. Grid #1 current is plotted for a positive bias of +2 V. The screen grid current is high at low plate voltages but drops to a stable, lower level once the plate voltage exceeds 50 V.
  • Plate Characteristics (Ec2 = 90 V): These curves exhibit a similar profile to the 150 V curves, with both plate and screen currents scaled down proportionally.
  • Transfer Characteristics: The curves plotting plate current, screen current, transconductance, and plate resistance against Grid #1 voltage show that transconductance peaks near 0 V bias, reaching up to 2000 µmhos. Conversely, the plate resistance drops sharply as the control grid bias approaches 0 V.

Technical Summary

The 1AB5 is a filamentary remote-cutoff RF pentode designed for mixer and RF amplifier applications. Operating with a 1.2 V, 130 mA DC filament, it provides a higher transconductance than the 1LN5. The tube is housed in a T-9 glass envelope with either a 5-pin (5BP) or an 8-pin lock-in (5BF) base. Under typical Class A1 conditions at 150 V, it delivers a transconductance of 1350 µmhos and a plate resistance of 125,000 Ω, with remote-cutoff characteristics extending down to -23 V for a transconductance of 10 µmhos.

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
8BR
Socket code
-
Base pins
8
Nominal heater voltage
1.2 V
Nominal heater current
130 mA
Parallel heater voltage
-
Parallel heater current
-
Series capable
No

8BR - 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
125000 Ω
Transconductance
0.00135 S
Max plate voltage
150 V
Max screen voltage
150 V
Max plate dissipation
1 W
Max screen dissipation
0.3 W

Remote-cutoff RF pentode.

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

195X General Electric Essential Characteristics

Published operating points and test conditions from this source.

SECTION 1

Pentode

Capacitance

  • Input capacitance

    2.8 pF

  • Output capacitance

    4.2 pF

  • Grid-to-plate capacitance

    0.25 pF

Other

  • Plate voltage

    150 V

    ClassA

  • Screen voltage

    150 V

    ClassA

  • Grid voltage

    -1.5 V

    ClassA

  • Plate current

    6.8 mA

    ClassA

  • Screen current

    2 mA

    ClassA

  • Plate voltage

    90 V

    ClassA

  • Screen voltage

    90 V

    ClassA

  • Grid resistor

    1 Mohm

    ClassA

  • Plate current

    3.5 mA

    ClassA

  • Screen current

    0.8 mA

    ClassA

  • Plate resistance

    275000 ohm

    ClassA

  • Transconductance

    1100 uS

    ClassA

Data set 02

1961 Tung Sol

Published operating points and test conditions from this source.

SECTION 1

Pentode

Other

  • Plate voltage

    150 V

    ClassA

  • Grid 2 voltage

    150 V

    ClassA

Capacitance

  • Grid to plate

    0.025 pF