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Rectifier - Half Wave ·Rectifier

142

Machlett ML-142 high-vacuum rectifier for compact high-voltage industrial equipment, combining rugged thoriated-tungsten construction with up to approximately 100 kV inverse-voltage capability.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
-
Socket code
-
Base pins
-
Nominal heater
3.8 V / 6.6 A

Description

142 — High-Voltage Rectifier Tube

The 142 (also designated as the ML-142) is a high-vacuum rectifier tube designed for high-voltage applications with moderate power requirements. It is characterized by its compact physical size, low internal voltage drop, and high peak inverse voltage capability. The tube is designed to operate in either oil or air insulating mediums, making it highly adaptable for various high-voltage power supply configurations.

Construction and Mechanical Design

The 142 incorporates specialized construction features designed to ensure mechanical ruggedness, long operating life, and stable electrical performance under high electrostatic stress.

  • Cathode: The tube features a low-wattage, thoriated-tungsten, catenary-type filament. This design allows for close anode-to-cathode spacing without the risk of filament distortion caused by electrostatic forces.
  • Anode: A cylindrical molybdenum anode is utilized, providing a high rate of heat dissipation and an adequate safety factor to protect against accidental overload conditions.
  • Cooling and Mounting: The tube is cooled via radiation. It can be mounted in any optional position.
  • Insulating Medium: The tube can be operated in either oil or air. The choice of insulating medium directly affects the maximum voltage ratings.
  • Physical Dimensions and Weight:
    • Net Weight: 7 ounces.
    • Overall Length: 8-1/16 inches ± 1/16 inch.
    • Maximum Diameter: 2-1/4 inches at the base collar, with a body diameter of 2 inches.
    • Anode Terminal (Top Cap) Diameter: 0.566 inch ± 0.007 inch.

Filament and Electrical Characteristics

The thoriated-tungsten filament requires precise voltage control to maximize the service life of the tube. The electrical characteristics of the filament and basic operating parameters are as follows:

ParameterValue
Filament Voltage3.8 V
Filament Current (approximate, at 3.8 V)6.6 A
Calculated Filament Power25.08 W
Minimum Filament Heating Time2 seconds
Maximum Tube Voltage Drop (at 0.30 A)360 V

The applied filament voltage must be maintained within ±5% of the rated 3.8 V. For maximum tube life, it is recommended to maintain the filament voltage as close as possible to the rated value under all operating conditions. The minimum filament heating time of 2 seconds must be observed before anode voltage is applied.

Maximum Ratings and Circuit Applications

The maximum ratings of the 142 depend heavily on the insulating medium used (oil or air) and the specific circuit configuration.

Absolute Maximum Ratings

  • Peak Inverse Anode Voltage (Oil Insulation): 100,000 V (100 PKV)
  • Peak Inverse Anode Voltage (Air Insulation): 50,000 V (50 PKV)
  • Peak Anode Current: 0.300 A (300 mA)
  • Anode Dissipation: 25 W

Average D-C Load Current Ratings

The average direct-current load ratings vary depending on whether the circuit is unfiltered (sine-wave input and resistance load without inductive or capacitive effects) or filtered (sine-wave voltage input and inductive choke input filter):

Circuit ConfigurationUnfiltered Load CurrentFiltered Load Current
Single-phase, two-tube, half-wave0.075 A—
Single-phase, four-tube, full-wave0.150 A0.200 A
Three-phase, double-Y parallel0.450 A0.450 A
Three-phase, full-wave0.225 A0.225 A

Performance Curves and Tube Voltage Drop

The relationship between peak anode current and peak anode voltage is defined by the tube's characteristic curve at the nominal filament voltage of 3.8 V.

At lower anode voltages, the current rises steadily:

  • At a peak anode voltage of approximately 200 V, the peak anode current is about 100 mA.
  • At approximately 300 V, the current reaches 200 mA.
  • At approximately 400 V, the current reaches the rated maximum peak anode current of 300 mA.

Beyond 400 V, the curve begins to bend as it approaches saturation:

  • At 600 V, the peak anode current is approximately 450 mA.
  • At 1000 V, the peak anode current reaches approximately 500 mA.
  • At 1400 V, the peak anode current levels off near 520 mA.

The maximum specified tube voltage drop is 360 V when conducting a current of 0.30 A, which is consistent with the typical performance curve.

Safety and Operational Requirements

Due to the high operating voltages of the 142, operation of this tube may produce x-rays. Adequate rayproof shielding must be provided in the equipment design to protect personnel from radiation exposure. Additionally, proper high-voltage insulation (either oil immersion or sufficient air clearance) must be maintained to prevent external flashover, especially when operating near the maximum peak inverse voltage limits of 100 PKV in oil or 50 PKV in air.

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
-
Socket code
-
Base pins
-
Nominal heater voltage
3.8 V
Nominal heater current
6.6 A
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

Rectifier

X-ray radiationInterelectrode capacitances
Max plate dissipation
25 W
Rectifier peak inverse voltage
100000 V
Rectifier peak forward current
300 mA
Rectifier forward voltage drop
360 V
Rectifier warm-up time
2 s

Promoted fields populated from explicitly published ratings/characteristics; service-specific data retained as parameters.

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

1971 Machlette Laboratories

Published operating points and test conditions from this source.

SECTION 1

Rectifier

Other

  • The ML

    142

    The ML-142 is a high-vacuum rectifier tube having a high-voltage applications. These features insure ruggedness,

  • maximum inverse voltage rating of

    100 mA

    maximum inverse voltage rating of 100 PKV using oil long life, low internal voltage drop and moderate average-

  • insulation or

    50 mA

    insulation or 50 PKV using air insulation and a maximum load-current capacity. The cathode is a low-wattage, thori-

  • peak anode current rating of

    300 mA

    peak anode current rating of 300 MA. It is especially suit- ated-tungsten, catenary-type filament, allowing close

  • Filament Voltage

    3.8

    Filament Voltage ... ... . ... ... 3.8 Vols*

  • Filament Current at [1]

    3.8 V

    Filament Current at 3.8 Volts, approximate 6.6 Amps

  • Filament Current at [2]

    6.6 V

    Filament Current at 3.8 Volts, approximate 6.6 Amps

  • Filament Heating Time, minimum

    2 s

    Filament Heating Time, minimum ... 2 Secs

  • * Applied filament voltage must be held within =

    5 mA

    * Applied filament voltage must be held within = 5% of rated voltage. For maximum life, ilament voltage should be main-

  • Peak Anode Current .......................... e,

    0.3

    Peak Anode Current .......................... e, 0.300 Amp

  • Anode Dissipation U UOURTRN

    25

    Anode Dissipation U UOURTRN 25 Warts

  • PEAK ANODE CURRENT —~ MILLIAMPERES

    1 A

    PEAK ANODE CURRENT —~ MILLIAMPERES 1