LL1682 50mA Lundahl Übertrager 5,5k 5Ohm / 9k 8Ohm SE 8W OPT
Fixed 5.5 kO to 5 O ratio suits EL84, 6V6 and triode stages in SET
Using 4 or 8 O reflects about 4.4 or 8.8 kO to the transformer primary
35 H, 200 V RMS at 30 Hz, 1.35 kg, C-core and 4 kV isolation overall
Lundahl LL1682/50mA – compact SE output transformer with 5.5 kΩ to 5 Ω
The Lundahl LL1682/50mA is a single-ended output transformer for valve stages operating at approximately 50 mA of quiescent plate current. Its fixed ratio reflects a 5 Ω speaker load as approximately 5.5 kΩ at the primary.
Changing the loudspeaker impedance changes the reflected primary load proportionally. The same transformer can therefore provide approximately 4.4 kΩ with 4 Ω or 8.8 kΩ with 8 Ω, provided that the resulting load suits the output-valve operating point.
Suitable applications
- Single-ended stages requiring a primary load around 4.5 to 5.5 kΩ
- Correctly designed EL84, 6V6GT, EL90 or EL95 output stages
- Triode-connected EL34, KT88 or related power valves at moderate current
- Directly or indirectly heated triode stages with a suitable load line
- Mono and stereo SET projects using one transformer per channel
- 4, 5 or 8 Ω speakers where the resulting primary load is deliberately required
Technical data
- Product type
- Single-ended valve output transformer
- Model version
- LL1682/50mA
- Official nominal match
- Approx. 5.5 kΩ plate load with a 5 Ω loudspeaker
- Reflected load with 4 Ω
- Calculated at approximately 4.4 kΩ; rounded by BTB to 4.5 kΩ
- Reflected load with 8 Ω
- Calculated at approximately 8.8 kΩ; rounded by BTB to 9 kΩ
- Turns ratio
- 16+16:1+1 or (5+11)+(5+11):1+1
- Magnetic SE operating point
- 50 mA according to the model version
- Primary inductance
- Approx. 35 H
- Maximum primary signal voltage
- Approx. 200 V RMS at 30 Hz
- Magnetic power limit
- Approx. 8 W at 30 Hz into 5 Ω; not a universal amplifier-output rating
- DC resistance of each primary winding
- Approx. 105 Ω
- Total primary resistance in series
- Approximately 210 Ω
- Secondary DC resistance
- Approx. 0.4 Ω in the documented parallel connection
- Thermal winding-current limit
- 160 mA through either primary winding; not a recommended SE bias current
- Winding-to-winding dielectric test
- 4 kV AC
- Winding-to-core dielectric test
- 2 kV AC
- Core
- Lundahl audio C-core
- Winding construction
- Four-section dual-coil construction with insulation foil between copper layers
- Dimensions
- Approx. 95 × 75 × 50 mm
- Mounting pattern
- Approx. 35 × 75 mm with four M4 mounting points
- Weight
- Approx. 1.35 kg
- Country of origin
- Sweden
Load matching without switchable secondary taps
- 5 Ω loudspeaker
- Provides the official nominal primary load of approximately 5.5 kΩ
- 4 Ω loudspeaker
- Reduces the reflected primary load to approximately 4.4 kΩ
- 8 Ω loudspeaker
- Raises the reflected primary load to approximately 8.8 kΩ
- Important selection rule
- Determine the required plate load from the valve, plate voltage, quiescent current and load line before selecting the loudspeaker impedance
Comparison of LL1682 versions
- LL1682/50mA
- 35 H of primary inductance and a 50 mA magnetic SE operating point
- LL1682/100mA
- 17 H of primary inductance for a greater magnetic quiescent current
- LL1682/PP
- Approximately 100 H, a 40 W magnetic limit at 30 Hz and documented 33% ultralinear connections
- Single-ended ultralinear operation
- Not documented in the standard SE drawing; the labelled UL connections belong to the push-pull arrangement
Selection and safety notes
The 8 W figure is a magnetic transformer limit at 30 Hz. Actual amplifier output depends on the output valve, plate voltage, quiescent current, operating mode and permitted plate dissipation.
An 8 Ω speaker is not automatically the correct choice merely because it can be connected. The resulting approximately 8.8 kΩ load must deliberately suit the output-valve load line.
Lethal plate voltage can be present on the open transformer. Install the LL1682 in a closed, touch-safe enclosure on a chassis capable of supporting its weight.
Questions about selection and use
Which SE output transformer suits an EL84 or 6V6GT stage operating around 50 mA with a 5 kΩ plate load?
Lundahl LL1682/50mA is a suitable starting point for a correctly designed EL84 or 6V6GT single-ended stage. A 5 Ω load provides approximately 5.5 kΩ; the valve voltage, quiescent current and dissipation must suit the load line.
Which Lundahl output transformer provides approximately 5.5 kΩ with a 5 Ω loudspeaker?
Lundahl LL1682/50mA provides this official nominal match. The 50 mA version offers 35 H of primary inductance and an 8 W magnetic limit at 30 Hz.
Can the LL1682/50mA operate with an 8 Ω loudspeaker?
Yes, the LL1682/50mA can operate with an 8 Ω loudspeaker, but it then reflects approximately 8.8 kΩ rather than 5.5 kΩ to the primary. This greater load must suit the output-valve operating point.
Is the LL1682/50mA suitable for a stereo SET amplifier?
Yes, the LL1682/50mA is suitable for a stereo SET amplifier using one transformer per channel. Both channels should use the same valves, loudspeaker load, wiring and core orientation.
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
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Source: IHK Mittelfranken
Tariff Number: 85043129
Country of Origin: SE