LL2742 250mA Lundahl Drossel Choke 17H 250mA / 4H 500mA
€132.80
Delivery time: ca. 1 - 5 days
Series gives 17 H/250 mA; parallel gives 4 H/500 mA supply operation
Saturation values of 350/700 mA are not continuous current ratings
80 O per coil, 1.35 kg, 95 × 75 × 50 mm and 4 kV isolation overall
Lundahl LL2742/250mA – high-current C-core choke for powerful valve supplies
The Lundahl LL2742/250mA is a dual-coil high-current B+ choke for substantial valve-amplifier power supplies. It provides 17 H at 250 mA recommended DC with both windings in series.
Connecting the windings in phase and in parallel provides 4 H at 500 mA recommended DC. Compared with lower-current LL2742 versions, this model prioritises substantially greater current capability.
Suitable applications
- High-current LC and CLC supplies for valve power amplifiers
- B+ supplies for large stereo and parallel push-pull amplifiers
- 17 H series operation at up to 250 mA recommended DC
- 4 H parallel operation at up to 500 mA recommended DC
- Choke-input supplies after calculation of minimum load and critical inductance
- Split common-mode filtering following the Lundahl connection diagram
Technical data
- Product type
- Dual-coil high-current B+ filter choke
- Model version
- LL2742/250mA
- Inductance with coils in series
- 17 H
- Recommended DC current in series
- 250 mA
- Saturation current in series
- Approx. 350 mA; not a recommended continuous current
- Inductance with coils in parallel
- 4 H
- Recommended DC current in parallel
- 500 mA
- Saturation current in parallel
- Approx. 700 mA; not a recommended continuous current
- DC resistance per winding
- Approx. 80 Ω
- Total resistance in series
- Approximately 160 Ω
- Equivalent resistance in parallel
- Approximately 40 Ω with equal current sharing
- Maximum dissipation for this version
- Approx. 10 W under the documented rated conditions
- Maximum ripple voltage in series
- Approx. 640 V RMS at 100 Hz and recommended DC current
- Maximum ripple voltage in parallel
- Approx. 320 V RMS at 100 Hz and recommended DC current
- Winding-to-winding dielectric test
- 4 kV AC
- Winding-to-core dielectric test
- 2 kV AC
- Core
- Lundahl audio C-core
- Dimensions
- Approx. 95 × 75 × 50 mm
- Mounting pattern
- Approx. 35 × 75 mm with four M4 mounting points
- Weight
- Approx. 1.35 kg
Winding connections
- First winding
- Pins 1 to 3, with the winding start at pin 1
- Second winding
- Pins 6 to 4, with the winding start at pin 6
- 17 H series connection
- Join pin 3 to pin 6 and use pins 1 and 4 as the terminals
- 4 H parallel connection
- Join pins 1 and 6 together and join pins 3 and 4 together with the correct phase
- Split common-mode filtering
- Implement only as shown in the complete manufacturer diagram and as part of a correctly designed supply
Voltage drop and thermal loading
At 250 mA, the approximately 160 Ω series connection produces a calculated drop of about 40 V and copper loss of 10 W. At 500 mA, the approximately 40 Ω parallel connection produces about 20 V and the same 10 W loss.
The substantial voltage drop must be included in the B+ design. Provide adequate ventilation and do not enclose the choke without checking its operating temperature.
At a substantially lower operating current, a lower-current LL2742 version can provide greater inductance and stronger filtering.
Choke-input and safety notes
Choke-input operation requires calculation of rectifier type, critical inductance, continuous minimum load and possible no-load voltage.
Lethal voltage and substantial stored energy may be present at the choke. Installation, wiring and safe discharge require suitable expertise.
Questions about selection and use
Is the Lundahl LL2742/250mA suitable for a high-current CLC supply operating at up to 250 mA?
Yes, the Lundahl LL2742/250mA is suitable in its 17 H series connection for a correctly designed LC or CLC supply operating at up to 250 mA recommended DC. Its calculated voltage drop of approximately 40 V at rated current must be considered.
Can the LL2742/250mA be connected in parallel as a 4 H, 500 mA choke?
Yes, the LL2742/250mA can operate with its windings connected in phase and in parallel as a 4 H choke for up to 500 mA recommended DC. Both windings and their wiring must share and carry the current safely.
Is the LL2742/250mA suitable for a high-power choke-input supply?
Yes, the LL2742/250mA can be used in a correctly calculated choke-input supply. Critical inductance, minimum load, rectifier current, dissipation and no-load voltage must suit the selected series or parallel connection.
Note: All brand names mentioned, such as Marshall, Fender, etc., are registered trademarks of their respective owners and are used here for descriptive and compatibility purposes only.
Lundahl Transformers AB
SE-76150 Norrtälje
Email: order@lundahltransformers.com
The EU Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (2011/65/EU = "RoHS 2") aims to exclude certain hazardous substances from electrical and electronic equipment or to restrict the use of certain substances in electrical and electronic equipment. These include substances such as lead, mercury, cadmium, and chromium, as well as certain brominated flame retardants and plasticizers. These substances may only be used in electrical and electronic equipment up to a maximum concentration limit, unless exemptions in the annexes to the directive permit their use under certain conditions. This can reduce and eliminate harmful substances and improve the recycling of waste electrical and electronic equipment. To find out whether the component you purchased from us is permitted in your device, please refer to the current directive or the current law applicable to your country. If you are a manufacturer, please feel free to contact us to find out whether the component you require can be tested and approved according to the current directives. We would be happy to assist you.
Fact sheet on EU Directive 2011/65/EURestriction of the use of hazardous substances in electrical and electronic equipment (PDF, not accessible, 2 MB)
Source: IHK Mittelfranken
Tariff Number: 85043180000
Country of Origin: DE
Weight: 1,35 kg