LL9202 50mA SE AÜ Übertrager Ra 6,5k 11k output transformer

Lundahl LL9202/50mA – high-impedance SE output transformer with 6.5, 11 or 23 kΩ

The Lundahl LL9202/50mA is a large single-ended output transformer for high-voltage valve stages. Its divided windings provide primary loads of approximately 6.5, 11 or 23 kΩ together with several 4, 8 and 16 Ω loudspeaker connections.

The 50 mA version uses a 225 µm air gap and provides approximately 100 H of primary inductance. It is designed for lower magnetic quiescent current and greater primary inductance than the 85 mA version.

Suitable applications

• 211 single-ended output stages with a correctly calculated load line
• Other high-voltage triodes operating near a 50 mA magnetic quiescent current
• Primary loads of 6.5, 11 or 23 kΩ
• 4, 8 and 16 Ω loudspeakers using the documented secondary arrangements
• Mono and stereo high-voltage amplifiers using one transformer per channel
• Circuits where greater primary inductance takes priority over additional DC-current capability

Technical data

Product type

Single-ended valve output transformer for high primary impedances

Model version

LL9202/50mA

Magnetic SE operating point

50 mA at approximately 0.9 T

Air gap

Approx. 225 µm

Primary inductance

Approx. 100 H

Primary impedances

Approx. 6.5, 11 or 23 kΩ including transformer copper resistance

Secondary impedances

4, 8 or 16 Ω, depending on the primary load and secondary arrangement

Turns ratio

4 × 26.5:8 × 1

Primary DC resistance

Approx. 600 Ω with all sections in series, comprising four sections of approximately 150 Ω

Secondary DC resistance

Approx. 0.4 Ω average per secondary section

Primary leakage inductance

Approx. 20 mH

Thermal primary-current limit

110 mA according to the documented 7 W winding-loss criterion; not a recommended SE bias current

Maximum primary signal voltage

Approx. 525 V RMS at 30 Hz in single-ended operation

Magnetic power limit at 23 kΩ

Approx. 13 W at 30 Hz

Magnetic power limit at 11 kΩ

Approx. 25 W at 30 Hz

Magnetic power limit at 6.5 kΩ

Approx. 50 W at 30 Hz

Winding loss

Approximately 0.2, 0.5 or 0.8 dB depending on the primary load

Numerical frequency response

Not stated separately for the LL9202/50mA in the current series data sheet

Primary-to-secondary dielectric test

3 kV AC

Winding-to-core dielectric test

1.5 kV AC

Core

Lundahl audio C-core

Winding construction

Harmonically sectioned primary and secondary windings with low leakage inductance and capacitance

Construction

Open-frame transformer for installation inside a closed amplifier enclosure

Dimensions

Approx. 118 × 85 × 78 mm

Mounting pattern

Approx. 53 × 90 mm with four M4 mounting points

Weight

Approx. 2.5 kg

Primary loads and loudspeaker connections

23 kΩ plate load

8 Ω using secondary Alternative B or 16 Ω using Alternative C; no documented standard 4 Ω connection

11 kΩ plate load

4 Ω using Alternative B, 8 Ω using Alternative C or 16 Ω using Alternative D

6.5 kΩ plate load

4 Ω using Alternative C, 8 Ω using Alternative D or 16 Ω using Alternative E

Connection view

Follow the Lundahl underside-view drawing exactly for every primary and secondary link

Choosing the primary load

6.5 kΩ

Tends towards greater plate current and potentially more output; verify valve dissipation carefully

11 kΩ

Intermediate load for several high-voltage triodes and more conservative operating points

23 kΩ

High primary load with lower signal current and particularly large required voltage swing

Comparison with the 85 mA version

The LL9202/50mA provides 100 H, more primary inductance than the 57 H of the LL9202/85mA. At an operating point near 50 mA, this can provide greater small-signal low-frequency reserve.

The 85 mA version instead uses a larger air gap and is intended for greater magnetic DC loading. The actual quiescent current should therefore remain reasonably close to the selected version.

Voltage drop and safety

At 50 mA, approximately 600 Ω of primary DC resistance produces a calculated drop of about 30 V and copper loss of approximately 1.5 W. Include this voltage drop in the valve operating point.

The 30 Hz power figures are magnetic transformer limits rather than guaranteed amplifier output. The output valve, power supply, driver and permitted plate dissipation limit the complete amplifier.

Immediately lethal high voltage can be present on the open transformer. Install it in a closed, touch-safe and mechanically secure enclosure.

Questions about selection and use

Which SE output transformer suits a 211 stage operating near 50 mA with an 11 or 23 kΩ plate load?

Lundahl LL9202/50mA is designed for a 50 mA magnetic operating point and provides 11 and 23 kΩ plate loads. The plate voltage, dissipation, valve resistance and required signal swing must suit the actual load line.

Which Lundahl SE output transformer provides 6.5, 11 and 23 kΩ in one model?

Lundahl LL9202/50mA provides these three primary loads together with documented 4, 8 or 16 Ω secondary arrangements. Not every primary load supports all three speaker impedances.

Can the LL9202/50mA operate below 50 mA of quiescent current?

Yes, the LL9202/50mA can operate at a lower current when the primary load, voltage swing and valve operating point remain suitable. The 50 mA figure remains the documented magnetic design point.

Can the LL9202/50mA be matched to 4, 8 and 16 Ω loudspeakers?

Yes, the LL9202/50mA provides suitable connections depending on the primary load. The 11 and 6.5 kΩ loads support 4, 8 and 16 Ω, while the 23 kΩ load supports 8 and 16 Ω.