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Voltage Triode Pentode ·Pentode-Triode

25B8GT

Combined triode and RF pentode for receiving and signal-amplifier service.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
2
Base
8T
Socket code
IO
Base pins
8
Nominal heater
25 V / 150 mA

Description

Combined triode and RF pentode.

Socket description

International Octal

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
8T
Socket code
IO
Base pins
8
Nominal heater voltage
25 V
Nominal heater current
150 mA
Parallel heater voltage
-
Parallel heater current
-
Series capable
No

8T - Terminal pinout

Electrical assignments shared by every tube using this base designation.

No verified pinout is recorded for this base designation.

Section ratings

2 physical sections, each with unique specifications.

Section 1

Triode

X-ray radiationInterelectrode capacitances
Plate resistance
75000 Ω
Transconductance
0.0015 S
Amplification factor
112.5
Max plate voltage
100 V

Source-defined physical/function section.

Section 2

Pentode

X-ray radiationInterelectrode capacitances
Plate resistance
185000 Ω
Transconductance
0.002 S
Amplification factor
370
Max plate voltage
100 V
Max screen voltage
100 V

Source-defined physical/function section.

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 Ken Rad

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

  • Plate Voltage

    100 V

    Plate Voltage 100 Volts

  • Grid Voltage

    -1 V

    Grid Voltage -1 Volt

  • Plate Current

    60 mA

    Plate Current .60 Milliampere

  • Mutual Conductance

    1500 µS

    Mutual Conductance 1,500 Micromhos

  • Plate Resistance

    75 Mohm

    Plate Resistance .075 Megohm

  • Amplification Factor

    112.5 ratio

    Amplification Factor ) 112.5

  • Grid Voltage

    -2.5 V

    Approximate Grid Voltage For Plate Current Cut-Off -2.5 Volts

SECTION 2

Pentode

Other

  • Plate Voltage

    100 V

    Plate Voltage 100 Volts

  • Screen Voltage

    100 V

    Screen Voltage 100 Volts

  • Grid Voltage

    -3 V

    Grid Voltage -3 Volts

  • Plate Current

    7.6 mA

    Plate Current 7.6 Milliamperes

  • Screen Current

    2 mA

    Screen Current 2.0 Milliamperes

  • Mutual Conductance

    2000 µS

    Mutual Conductance 2,000 Micromhos

  • Amplification Factor

    370 ratio

    Amplification Factor 370

  • Plate Resistance

    185 Mohm

    Plate Resistance .185 Megohm

  • Grid Voltage

    -41 V

    Control Grid Voltage For Sm = 2 Micromhos -41 Volts

Data set 02

1948 Brimar Radio Valve Manual

Published operating points and test conditions from this source.

SECTION 1

Triode

Characteristic

  • HeaterOrFilamentVoltage

    25 V

  • HeaterOrFilamentCurrent

    150 mA

Data set 03

195X General Electric Essential Characteristics

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

  • Plate voltage

    100 V

    ClassA

  • Grid voltage

    -1 V

    ClassA

  • Plate current

    0.6 mA

    ClassA

Characteristic

  • Amplification factor

    112

    ClassA

SECTION 2

Pentode

Other

  • Plate voltage

    100 V

    ClassA

  • Screen-grid voltage

    100 V

    ClassA

  • Grid voltage

    -3 V

    ClassA

  • Plate current

    7.6 mA

    ClassA

  • Screen-grid current

    2 mA

    ClassA

Data set 04

1961 Tung Sol

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

  • Heater voltage

    25 V

    Nominal

  • Heater current

    150 mA

    Nominal

  • Plate voltage

    100 V

    ClassA

  • Grid voltage

    -1 V

    ClassA

Characteristic

  • Plate current

    0.6 mA

    ClassA

  • Plate resistance

    75000 ohm

    ClassA

  • Transconductance

    1500 uS

    ClassA

  • Amplification factor

    112.5

    ClassA

  • Grid voltage for plate-current cutoff

    -2.5 V

    ClassA

Capacitance

  • Control grid to cathode

    5 pF

    Direct interelectrode capacitance

  • Plate to cathode

    4.6 pF

    Direct interelectrode capacitance

  • Control grid to plate

    2.2 pF

    Direct interelectrode capacitance

SECTION 2

Pentode

Other

  • Heater voltage

    25 V

    Nominal

  • Heater current

    150 mA

    Nominal

  • Plate voltage

    100 V

    ClassA

  • Screen voltage

    100 V

    ClassA

  • Control-grid voltage

    -3 V

    ClassA

Characteristic

  • Plate current

    7.6 mA

    ClassA

  • Screen current

    2 mA

    ClassA

  • Plate resistance

    185000 ohm

    ClassA

  • Transconductance

    2000 uS

    ClassA

  • Amplification factor

    370

    ClassA

  • Control-grid voltage for transconductance 2 uS

    -41 V

    ClassA

Capacitance

  • Control grid to cathode

    5.5 pF

    Direct interelectrode capacitance

  • Plate to cathode

    10 pF

    Direct interelectrode capacitance

  • Control grid to plate

    0.02 pF

    Direct interelectrode capacitance

  • Pentode control grid to triode grid

    0.02 pF

    Cross-section capacitance

  • Pentode control grid to triode plate

    0.009 pF

    Cross-section capacitance

  • Pentode plate to triode grid

    0.075 pF

    Cross-section capacitance