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

Specialized - Thyratron ·Triode

NL740

Quick-heating industrial gas-and-mercury thyratron for heavy ignitor firing, motor-speed control, and regulated rectifier equipment.

Directly heatedCold cathodeCommon cathodeDissimilarSpecialized
Sections
1
Base
DOWN
Socket code
SJ4
Base pins
-
Nominal heater
2.5 V / 16 A

Description

NATIONAL POWER TUBE NL-740 is a quick heating Industrial thyratron designed especially for heavy duty ignitor firing applications and for use in motor speed control and regulated rectifier equipments. It is gas and mercury filled for quick starting and constancy of characteristics within wide temperature limits. NL-741 has the same general characteristics, within its narrower temperature limits, but is filled with mercury only to permit use of the tube at higher voltages. Both types are available with bracket type bases for panel mounting under

Socket description

Super-jumbo 4-contact bayonet

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
DOWN
Socket code
SJ4
Base pins
-
Nominal heater voltage
2.5 V
Nominal heater current
16 A
Parallel heater voltage
-
Parallel heater current
-
Series capable
No

DOWN - 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

Triode

X-ray radiationInterelectrode capacitances
Max plate voltage
1500 V
Max cathode current
4 A
Rectifier peak inverse voltage
1500 V
Rectifier nominal output current
4 A
Rectifier peak forward current
50 A
Rectifier warm-up time
30 s

Published ratings and characteristics promoted where canonical fields apply.

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

1956 National Electronics Industrial Tubes

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

  • 4 Amperes do

    50 Amperes Peak A

    Source technical-information table; wording preserved from datasheet.

  • NL-740

    NL-741

    Source technical-information table; wording preserved from datasheet.

  • do Amperes output (maximum)

    4.0 | 2.5 | 4.0 | 2.5 | 2.5 A

    Source technical-information table; wording preserved from datasheet.

  • Instantaneous Amperes output (maximum)

    30 | 50 | 30 | 50 | 15 A

    Source technical-information table; wording preserved from datasheet.

  • anode current (seconds)

    _ | 5 | 5 | 5 | 5 | 5 A

    Source technical-information table; wording preserved from datasheet.

  • Maximum peak inverse volts

    1500 | 1500 | 1500 | 1500 | 5000 V

    Source technical-information table; wording preserved from datasheet.

  • Maximum peak forward volts

    _ | 1500 | 1500 | 1500 | 1500 | 2500 V

    Source technical-information table; wording preserved from datasheet.

  • Condensed mercury temperature limits (°C)

    —40 to #80 | —40 to+80 | +40 to +90 +40 to +90 +40 to +65 C

    Source technical-information table; wording preserved from datasheet.

  • Filament volts

    2.5 V

    Source technical-information table; wording preserved from datasheet.

  • Filament amperes

    16t 2 A

    Source technical-information table; wording preserved from datasheet.

  • Heating time (seconds)

    30 s

    Source technical-information table; wording preserved from datasheet.

  • before conduction (volts)

    500 V

    Source technical-information table; wording preserved from datasheet.

  • during conduction (volts)

    10 V

    Source technical-information table; wording preserved from datasheet.

  • Maximum critical grid current (microamps)

    10 A

    Source technical-information table; wording preserved from datasheet.

  • Maximum ac short circuit current (amperes)

    400 A

    Source technical-information table; wording preserved from datasheet.

  • above ambient (°C)

    25

    Source technical-information table; wording preserved from datasheet.

  • Net weight (ounces)

    __ | 7 oz

    Source technical-information table; wording preserved from datasheet.

  • Approx. shipping weight (Ibs.)

    _ | 4 lb

    Source technical-information table; wording preserved from datasheet.

  • 566 DIA

    .566" CIA.

    Source technical-information table; wording preserved from datasheet.

  • CI-5

    CI -5

    Source technical-information table; wording preserved from datasheet.

  • NL-741

    NL-741P

    Source technical-information table; wording preserved from datasheet.

  • MAX+

    1000

    Source technical-information table; wording preserved from datasheet.

  • GRID

    FLEX18 LE

    Source technical-information table; wording preserved from datasheet.

  • RETURNS TO FILAMENT CENTER TAP

    Litho II^.r6

    Source technical-information table; wording preserved from datasheet.

Characteristic

  • Typical arc drop at 12 amperes peak (volts)

    12 V

    Source technical-information table; wording preserved from datasheet.

  • Ionization time (approx., microseconds)

    10 us

    Source technical-information table; wording preserved from datasheet.

  • Deionization time (approx., microseconds)

    1000 us

    Source technical-information table; wording preserved from datasheet.

  • Anode to grid capacitance (uuf)

    3 pF

    Source technical-information table; wording preserved from datasheet.

Data set 02

1957 National Electronics

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

  • Maximum peak forward voltage

    1500 V

  • Maximum peak output current

    50 A

  • Maximum dc output current

    4 A