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

Rectifier - Full Wave ·Rectifier-Rectifier

12DF5

Twin-diode full-wave rectifier with separate cathodes and a center-tapped heater, suitable for capacitor-input and choke-input filter supplies. The separate cathodes provide flexible power-supply circuit arrangements.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
2
Base
9B5
Socket code
B9A
Base pins
9
Nominal heater
12.6 V / 450 mA

Description

12DF5 — Double Diode Miniature Full-Wave Rectifier

The 12DF5 is a miniature double diode full-wave rectifier designed for power supply applications requiring relatively high output current capabilities. It features a center-tapped heater, separate cathode connections, and a compact 9-pin miniature construction.

Construction, Physical Dimensions, and Pinout

The 12DF5 is constructed in a T-6 1/2 glass bulb with a miniature button 9-pin base (9BS). The tube is designed to be mounted in any position.

Physical Dimensions

  • Maximum overall length: 2 3/8 inches
  • Maximum seated height: 2 1/8 inches
  • Maximum diameter: 7/8 inches

Heater and Cathode Design

The tube features a coated unipotential cathode and a center-tapped heater. This center-tapped configuration allows the heater to be operated in either a series or parallel arrangement:

  • Series connection: 12.6 V at 0.45 A
  • Parallel connection: 6.3 V at 0.9 A

The heater can be supplied with either AC or DC.

Pin Connections

The 9BS base provides separate connections for each cathode and plate, allowing independent operation of the two diode sections. The pinout configuration, viewed from the bottom of the tube, is as follows:

PinConnection
1Cathode (Diode 1) [1K]
2No Connection [NC]
3Plate (Diode 2) [2P]
4Heater [H]
5Heater [H]
6Plate (Diode 1) [1P]
7No Connection [NC]
8Cathode (Diode 2) [2K]
9Heater Tap [HT]

Maximum Ratings

The 12DF5 is rated for rectifier service under the following absolute limits:

ParameterRating
Maximum peak inverse plate voltage1275 V
Maximum AC plate supply voltage (each plate, RMS)450 V
Maximum steady-state peak plate current (each plate)350 mA
Maximum transient peak plate current (each plate)2.0 A
Maximum AC heater-cathode voltage (RMS)225 V
Maximum DC heater-cathode voltage (heater negative with respect to cathode)450 V
Maximum DC output currentSubject to operating curves

Typical Operating Conditions and Characteristics

Under typical operating conditions, the 12DF5 exhibits an average tube voltage drop of 40 V when each plate is conducting 100 mA.

The tube can be operated in full-wave rectifier circuits using either capacitor-input or choke-input filters. Typical operating parameters for both configurations are detailed below:

ParameterCapacitor InputChoke Input
Heater Voltage (Series / Parallel)12.6 V / 6.3 V12.6 V / 6.3 V
Heater Current (Series / Parallel)0.45 A / 0.9 A0.45 A / 0.9 A
AC Plate Supply Voltage per Plate (RMS, no load)325 V450 V
Filter Input Condenser40 µF—
Filter Input Choke—10 H
Effective Plate Supply Resistance per Plate82 Ω—
DC Output Current at Filter100 mA100 mA
DC Output Voltage at Filter330 V360 V

Rectifier Performance and Design Considerations

The operational limits of the 12DF5 are highly dependent on the choice of filter input and the operating plate supply voltage.

DC Output Current Limits

The maximum permissible DC output current varies with the applied AC plate supply voltage. For choke-input filters, the maximum DC output current remains constant at approximately 63 mA per plate for supply voltages up to 320 V RMS, after which it decreases to 50 mA per plate at 450 V RMS. For capacitor-input filters, the maximum DC output current is also 63 mA per plate at low voltages but begins to decrease earlier, falling to approximately 45 mA per plate at 350 V RMS and further to 31 mA per plate at 450 V RMS.

Rectification Efficiency

In capacitor-input configurations, the area of permissible operation is bounded by a steady-state peak plate current limit of 350 mA per plate. The relationship between rectification efficiency (defined as the ratio of DC output voltage at the filter input to the peak AC input voltage per plate without load) and the DC output current per plate defines the safe operating region.

Transient Protection and Plate Supply Resistance

To prevent damage from transient peak currents during startup or switching, a minimum effective plate supply resistance must be present in each plate circuit when using a capacitor-input filter. This resistance limits the transient peak plate current to a maximum of 2.0 A. The minimum required resistance increases with the AC plate supply voltage:

  • At 200 V RMS plate supply, the required minimum resistance is 0 Ω.
  • At 300 V RMS plate supply, the minimum resistance is approximately 75 Ω.
  • At 400 V RMS plate supply, the minimum resistance is approximately 140 Ω.
  • At 450 V RMS plate supply, the minimum resistance is approximately 170 Ω.

Technical Summary

The 12DF5 is a versatile, 9-pin miniature double diode full-wave rectifier featuring separate cathode connections and a center-tapped heater for 6.3 V or 12.6 V operation. With a peak inverse voltage rating of 1275 V and a steady-state peak plate current rating of 350 mA per plate, it is well-suited for compact power supply designs. When operating in typical full-wave rectifier circuits, it delivers a DC output of 100 mA at 330 V (capacitor input) or 360 V (choke input). Designers must ensure that the minimum effective plate supply resistance is maintained in capacitor-input circuits to limit transient currents to the rated 2.0 A maximum.

Socket description

Small-button Noval 9-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
9B5
Socket code
B9A
Base pins
9
Nominal heater voltage
12.6 V
Nominal heater current
450 mA
Parallel heater voltage
6.3 V
Parallel heater current
900 mA
Series capable
Yes

9B5 - 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

Rectifier

X-ray radiationInterelectrode capacitances
Rectifier peak inverse voltage
1275 V
Rectifier nominal output current
100 mA
Rectifier peak forward current
350 mA
Rectifier forward voltage drop
40 V
Rectifier max heater-cathode voltage
450 V

Representative row for identical repeated diode/triode sections.

Section 2

Rectifier

X-ray radiationInterelectrode capacitances
Rectifier peak inverse voltage
1275 V
Rectifier nominal output current
100 mA
Rectifier peak forward current
350 mA
Rectifier forward voltage drop
40 V
Rectifier max heater-cathode voltage
450 V

Physical rectifier section 2; electrical properties populated from the same published ratings applicable to the identical rectifier path.

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

1961 Tung Sol

Published operating points and test conditions from this source.

SECTION 1

Rectifier

Other

  • AC Plate Supply Voltage Per Plate

    450 V

  • SteadyStatePeakPlateCurrentPerPlate

    350 mA

  • TransientPeakPlateCurrentPerPlate

    2 A

  • HeaterCathodeVoltageRMSMaximum

    225 V

SECTION 2

Rectifier

Other

  • AC Plate Supply Voltage Per Plate

    450 V

  • AC Plate Supply Voltage Per Plate

    450 V

  • SteadyStatePeakPlateCurrentPerPlate

    350 mA

  • SteadyStatePeakPlateCurrentPerPlate

    350 mA

  • TransientPeakPlateCurrentPerPlate

    2 A

  • TransientPeakPlateCurrentPerPlate

    2 A

  • HeaterCathodeVoltageRMSMaximum

    225 V

  • HeaterCathodeVoltageRMSMaximum

    225 V

Data set 02

1966 Tung Sol Electronic Tubes 2 of 4

Published operating points and test conditions from this source.

SECTION 1

Rectifier

Other

  • Maximum AC plate supply voltage each plate RMS

    450 V

    FullWaveRectifier

  • Maximum transient peak plate current each plate

    2 A

    FullWaveRectifier

  • Maximum AC heater-cathode voltage RMS

    225 V

    FullWaveRectifier

  • Typical AC plate supply voltage

    325 V

    CapacitorInputFilter

  • Filter input capacitor

    40 uF

    CapacitorInputFilter

  • DC output current at filter

    100 mA

    CapacitorInputFilter

  • DC output voltage at filter

    330 V

    CapacitorInputFilter

  • Typical AC plate supply voltage

    450 V

    ChokeInputFilter

  • Filter input choke

    10 H

    ChokeInputFilter

  • DC output current at filter

    100 mA

    ChokeInputFilter

  • DC output voltage at filter

    360 V

    ChokeInputFilter

SECTION 2

Rectifier

Other

  • Maximum AC plate supply voltage each plate RMS

    450 V

    FullWaveRectifier

  • Maximum AC plate supply voltage each plate RMS

    450 V

    FullWaveRectifier

  • Maximum transient peak plate current each plate

    2 A

    FullWaveRectifier

  • Maximum transient peak plate current each plate

    2 A

    FullWaveRectifier

  • Maximum AC heater-cathode voltage RMS

    225 V

    FullWaveRectifier

  • Typical AC plate supply voltage

    325 V

    CapacitorInputFilter

  • Filter input capacitor

    40 uF

    CapacitorInputFilter

  • DC output current at filter

    100 mA

    CapacitorInputFilter

  • DC output voltage at filter

    330 V

    CapacitorInputFilter

  • Typical AC plate supply voltage

    450 V

    ChokeInputFilter

  • Filter input choke

    10 H

    ChokeInputFilter

  • DC output current at filter

    100 mA

    ChokeInputFilter

  • DC output voltage at filter

    360 V

    ChokeInputFilter