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Voltage Pentode - High Frequency (single) ·Pentode

1B4

Directly heated high-frequency amplifier pentode, explicitly co-designated 1B4/951 in RCA documentation. It is intended for RF signal amplification and uses a filamentary cathode suited to low-voltage supply operation.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
-
Socket code
-
Base pins
5
Nominal heater
2 V / 60 mA

Description

1B4 — Filament-Type R-F Amplifier Pentode

The 1B4 is a filament-type pentode vacuum tube designed primarily for radio-frequency (R-F) amplification and detection in battery-operated receivers. It shares similar application characteristics with the older type 32 pentode but is housed in a more compact glass envelope.

Mechanical Specifications and Pin Connections

The 1B4 is constructed using an ST-12 glass bulb, featuring a small metal top cap and a small 4-pin base. Its physical dimensions are specified as follows:

  • Maximum Diameter: 1-3/16 inches
  • Overall Height: 4-9/32 to 4-17/32 inches
  • Seated Height: 3-11/16 to 3-31/32 inches

Pinout Configuration

The electrical connections are distributed between the base pins and an unnumbered terminal, alongside the top cap:

  • Pin 1: Plate (P)
  • Pin 2: Grid No. 1 / Control Grid (G1)
  • Pin 3: Grid No. 2 / Screen Grid (G2)
  • Pin 4: Grid No. 3 / Suppressor Grid (G3) & Filament negative (F-)
  • Unnumbered Pin: Filament positive (F+)
  • Top Cap: Small metal cap

Filament Ratings

The 1B4 is designed for low-power battery-operated equipment, utilizing a directly heated filament with the following electrical ratings:

  • Filament Voltage (D.C.): 2.0 Volts
  • Filament Current: 0.060 Ampere
  • Calculated Filament Power: 0.12 Watts (calculated from 2.0 V * 0.060 A)

Electrical Characteristics and Typical Operation

The 1B4 can be operated under different voltage conditions. The table below outlines the typical operating parameters for two distinct configurations, including the maximum rated limits for plate and screen voltages.

ParameterTypical Operation (90 V)Maximum Operation (180 V)
Plate Voltage90 V180 V (Max)
Screen Voltage (Grid No. 2)67.5 V (Max)67.5 V (Max)
Grid Voltage (Grid No. 1)-3 V-3 V
Plate Current1.6 mA1.7 mA
Screen Current0.7 mA0.6 mA
Plate Resistance1.0 Megohm1.5 Megohms
Amplification Factor5501000
Transconductance600 µmhos650 µmhos
Grid Voltage for Plate Cut-off (Approx.)-8 V-8 V

Interelectrode Capacitances

When measured in conjunction with an external shield-can, the interelectrode capacitances of the 1B4 are:

  • Grid-to-Plate Capacitance: 0.007 pF (max)
  • Input Capacitance: 5 pF
  • Output Capacitance: 11 pF

Application and Installation Guidelines

The primary application of the 1B4 is as an R-F amplifier or detector in battery-powered radio receivers.

  • Installation: For installation practices and mounting considerations, reference is made to the guidelines established for the type 34 tube.
  • Application: For detailed circuit application methods, reference is made to the type 32 tube, which shares a similar operational profile but differs in bulb size.

Characteristic Curves and Behavior

The average plate characteristics of the 1B4 are plotted at a constant filament voltage of 2.0 Volts D.C. and a screen grid voltage of 67.5 Volts. The control-grid voltage curves span from 0 to -7 Volts.

The curves reveal the following qualitative behaviors:

  • Low-Voltage Region: Below 50 plate volts, the plate current exhibits a sharp, rapid rise.
  • Pentode Region: Above 50 plate volts and extending up to 400 plate volts, the tube displays flat, classic pentode plate current characteristics, indicating high plate resistance.
  • Saturation: At a control-grid bias of 0 V, the plate current saturates near 4 mA.

Technical Summary

The 1B4 is a compact, filament-type pentode designed for efficient R-F amplification and detection in battery-operated receivers. Operating with a 2.0 V, 0.060 A filament, it provides high plate resistance (up to 1.5 Megohms) and an amplification factor of up to 1000 under maximum operating conditions (180 V plate, 67.5 V screen). Housed in an ST-12 envelope with a small 4-pin base and a top cap, its physical design is smaller than the functionally similar type 32, making it suitable for space-constrained battery receiver designs.

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
-
Socket code
-
Base pins
5
Nominal heater voltage
2 V
Nominal heater current
60 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
1500000 Ω
Transconductance
0.00065 S
Amplification factor
975
Max plate voltage
180 V
Max screen voltage
67.5 V
Max cathode current
3 mA

Published maximum ratings and electrical characteristics promoted from the approved source.

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

1937 Raytheon Radio Receiving Tubes

Published operating points and test conditions from this source.

SECTION 1

Pentode

Other

  • Plate voltage

    90 V

    ClassA

  • Screen voltage

    67.5 V

    ClassA

  • Grid bias

    -3 V

    ClassA

  • Plate current

    1.6 mA

    PlateVoltage=90V

  • Screen current

    0.7 mA

    PlateVoltage=90V

  • Plate voltage

    180 V

    ClassA

  • Plate current

    1.7 mA

    PlateVoltage=180V

  • Screen current

    0.6 mA

    PlateVoltage=180V

Characteristic

  • Plate resistance

    1 MOhm

    PlateVoltage=90V

  • Transconductance

    600 uS

    PlateVoltage=90V

  • Plate resistance

    1.8 MOhm

    PlateVoltage=180V

  • Transconductance

    650 uS

    PlateVoltage=180V

  • Grid bias for plate-current cutoff

    -8 V

Capacitance

  • Grid-to-plate capacitance

    - to 0.007 pF

    WithTubeShield; Maximum

  • Input capacitance

    5 pF

  • Output capacitance

    11 pF

Data set 02

1940 RCA

Published operating points and test conditions from this source.

SECTION 1

Pentode

Other

  • HeaterVoltageNominal

    2 V

    Nominal

  • HeaterCurrentNominal

    60 mA

    Nominal

  • Maximum Plate Voltage

    180 V

  • Maximum Screen Voltage

    67.5 V

  • Maximum Cathode Current

    3 mA

Characteristic

  • Transconductance

    650 µS

    Typical

  • Plate Resistance

    1500000 ohm

    Typical