LL9202 85mA Lundahl SE OPT AÜ Ra 6,5k 11k output transformer

Lundahl LL9202/85mA – high-current SE output transformer for 845 and high-voltage triodes

The Lundahl LL9202/85mA is a large single-ended output transformer for high-voltage valve stages operating at increased plate current. Its winding arrangements provide primary loads of approximately 6.5, 11 or 23 kΩ.

The 85 mA version uses a 400 µm air gap and provides approximately 57 H of primary inductance. The larger gap supports greater magnetic DC loading than the 50 mA version but reduces primary inductance.

Suitable applications

• 845 single-ended output stages operating at approximately 85 mA with a suitable load line
• 211 and other high-voltage triodes at a compatible operating point
• 805 and related Class A2 stages with a separately designed power driver
• 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

Technical data

Product type

Single-ended high-voltage valve output transformer

Model version

LL9202/85mA

Magnetic SE operating point

85 mA at approximately 0.9 T

Air gap

Approx. 400 µm

Primary inductance

Approx. 57 H

Primary impedances

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

Secondary impedances

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

Turns ratio

4 × 26.5:8 × 1

Primary DC resistance

Approx. 600 Ω with all primary sections in series

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 7 W winding-loss criterion; not a recommended 110 mA SE operating point

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 LL9202/85mA 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

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

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

View

The manufacturer drawing uses the underside view

Selection for 845, 211 and 805 stages

An 845 can use a primary load around 6.5 or 11 kΩ, depending on plate voltage, quiescent current and intended output. A lower load tends towards greater current and valve stress, while a higher load requires greater voltage swing.

A 211 frequently uses a higher primary load and can require 11 or 23 kΩ at some operating points. Select the final value from the load line rather than the valve designation alone.

An 805 or another output valve operating with positive grid current requires real driver power. The LL9202 does not replace calculation of grid current, driver output and bias requirements.

Comparison with the 50 mA version

The LL9202/85mA supports greater magnetic DC loading through its larger air gap. Its primary inductance is 57 H rather than the 100 H of the 50 mA version.

Where the actual quiescent current remains closer to 50 mA, the 50 mA version can offer greater low-frequency reserve. At an operating point near 85 mA, the larger-gap version is the more appropriate magnetic design.

Voltage drop and safety

At 85 mA, approximately 600 Ω of primary resistance produces a calculated drop of about 51 V and copper loss of approximately 4.3 W. Include this in the supply voltage, plate dissipation and cooling design.

845, 211 and 805 stages use immediately lethal high voltage. Install the open output transformer inside a closed enclosure with adequate creepage and clearance distances.

Questions about selection and use

Which SE output transformer suits an 845 stage operating near 85 mA with a 6.5 or 11 kΩ plate load?

Lundahl LL9202/85mA is designed for an 85 mA magnetic operating point and provides 6.5 and 11 kΩ plate loads. The plate voltage, dissipation, quiescent current and required signal swing determine the appropriate connection.

Which high-voltage output transformer provides 23 kΩ in addition to 6.5 and 11 kΩ?

Lundahl LL9202/85mA provides all three primary loads within the same winding family. The 23 kΩ connection is documented for 8 or 16 Ω loudspeakers.

Can the LL9202/85mA operate at approximately 60 to 70 mA?

Yes, the LL9202/85mA can operate at a lower quiescent current when the load line and signal swing remain suitable. Where the operating point is closer to 50 mA, the 50 mA version with 100 H can provide greater bass reserve.

Can the LL9202/85mA match 11 kΩ to an 8 Ω loudspeaker?

Yes, documented secondary Alternative C provides approximately 11 kΩ with an 8 Ω loudspeaker. Follow the Lundahl connection drawing exactly for every winding link.