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

Rectifier - Half Wave ·Rectifier

148

Machlett high-vacuum rectifier for very-high-voltage supplies, voltage multipliers, and capacitor-energy-storage circuits, providing approximately 150 kV inverse-voltage capability with oil insulation.

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

Description

148 - High-Vacuum Rectifier Tube

The ML-148 is a high-vacuum rectifier tube designed specifically for high-power-level applications. It is characterized by its high peak power capability, making it highly suitable for use in voltage multiplier circuits, energy storage capacitor circuits, and other demanding power applications. The tube is engineered to provide ruggedness, a long operational life, low internal voltage drop, and a high average load current capacity.

Construction and Mechanical Specifications

The ML-148 incorporates specialized design features to ensure reliable operation under high electrostatic and thermal 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 offering an adequate safety factor against accidental thermal overload.
  • Cooling and Insulation: The tube is cooled via radiation. It is designed to operate in either air or oil insulating mediums, which directly affects its maximum voltage ratings.

The physical dimensions and mechanical properties of the ML-148 include:

  • Mounting Position: Optional (can be mounted in any orientation).
  • Net Weight: 16 ounces.
  • Overall Length: 10-1/2 inches (with a tolerance of +/- 1/16 inch).
  • Bulb Diameter: The center section of the tube has a diameter of 2-1/2 inches.
  • End Caps: The end caps have a diameter of 2-1/4 inches. The longer end cap measures 3-1/8 inches in length with a terminal pin that is 1 inch in diameter and 11/16 inch long. The shorter end cap measures 2 inches in length with a terminal pin that is 1/2 inch in diameter and 1/2 inch long.

Electrical Characteristics and Filament Ratings

The electrical parameters of the filament must be precisely maintained to ensure the longevity of the thoriated-tungsten cathode.

  • Filament Voltage: 5.7 Volts. The applied filament voltage must be held within +/- 5% of this rated value under all operating conditions to maximize the tube's life.
  • Filament Current: Approximately 6.6 Amperes at the rated voltage of 5.7 Volts.
  • Filament Heating Time: A minimum of 2 seconds must be allowed for the filament to heat before anode voltage is applied.
  • Tube Voltage Drop: The maximum tube voltage drop is 800 Volts when the anode current is at 1.0 Ampere.

Filament Power Calculation

  • Input Voltage: 5.7 V
  • Input Current: 6.6 A
  • Calculation: 5.7 V * 6.6 A = 37.62 Watts of nominal filament power.

Maximum Ratings and Circuit Applications

The maximum ratings of the ML-148 depend heavily on the insulating medium used and the specific circuit configuration.

Voltage and Current Limits

  • Peak Inverse Anode Voltage (Oil Insulation): 150,000 Volts (150 PKV)
  • Peak Inverse Anode Voltage (Air Insulation): 80,000 Volts (80 PKV)
  • Peak Anode Current: 1.0 Ampere
  • Anode Dissipation: 60 Watts

Average D-C Load Current Ratings

The allowable average direct-current load depends on the rectifier circuit configuration and whether the circuit is filtered or unfiltered:

Circuit ApplicationUnfiltered Load CurrentFiltered Load Current
Single-phase, two-tube, half-wave0.150 Amp—
Single-phase, four-tube, full-wave0.300 Amp0.320 Amp
Three-phase, double-Y parallel0.900 Amp0.900 Amp
Three-phase, full-wave0.450 Amp0.450 Amp

Note on operating conditions: Unfiltered load current ratings are based on a sine-wave input and a resistive load without any inductive or capacitive effects. Filtered load current ratings are based on a sine-wave voltage input and an inductive choke input filter.

Anode Current Characteristics

The relationship between the peak anode current and the peak anode voltage (at the nominal filament voltage of 5.7 V) demonstrates the tube's conduction characteristics:

  • At low anode voltages, such as 200 V, the peak anode current is minimal, remaining under 100 mA.
  • As the anode voltage increases, the current rises in a non-linear fashion. It reaches approximately 500 mA at a peak anode voltage of 600 V.
  • At approximately 850 V, the current reaches the rated peak anode current of 1.0 Ampere (1000 mA).
  • The curve continues upward, showing that the tube can conduct up to approximately 1.6 Amperes (1600 mA) when the peak anode voltage reaches 1200 V, though operational designs must respect the 1.0 Ampere maximum peak anode current rating.

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
5.7 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
60 W
Rectifier peak inverse voltage
150000 V
Rectifier peak forward current
1 A
Rectifier forward voltage drop
500 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

    148

    The ML-148 is a high-vacuum rectifier tube having a high-power-level applications. These features insure rug-

  • maximum inverse voltage rating of

    150 mA

    maximum inverse voltage rating of 150 PKV using oil gedness, long life, low internal voltage drop and high aver-

  • insulation or

    80 mA

    insulation or 80 PKV using air insulation and a maximum age-load-current capacity. The cathode is a low-wattage,

  • peak anode current rating of

    1

    peak anode current rating of 1.0 ampere. It is especially thoriated-tungsten, catenary-type filament, allowing close

  • Filament Voltage

    5.7 V

    Filament Voltage ... ...................................................... 5.7 Volts*

  • Filament Current at [1]

    5.7 V

    Filament Current at 5.7 Volts, approximate 6.6 Amps

  • Filament Current at [2]

    6.6 V

    Filament Current at 5.7 Volts, approximate 6.6 Amps

  • Filament Heating Time, minimum

    2 s

    Filament Heating Time, minimum ... ... ... ... . 2 Secs

  • * Applied filament voltage must be held within =

    59 mA

    * Applied filament voltage must be held within = 59 of rated voltage. For maximum life, ilament voltage should be main-

  • Peak Anode Current . I

    1

    Peak Anode Current . I 1.0 Amp

  • Anode Dissipation

    60

    Anode Dissipation .. .. ........ 60 Warts

  • Published value

    1

    1+Unfltered Load Current Ratings are basedon sine-wave inputandresistanceload wnthout inductive or capacitive effects.

  • Published value

    1

    1Filtered Load Current Ratings are based on sine-wave voltageinpur and inductive chokeinput filter.