LL9202 PP Lundahl Übertrager Ra 6,5k 11k output transformer

Lundahl LL9202/PP – high-voltage push-pull output transformer with 6.5, 11 or 23 kΩ

The Lundahl LL9202/PP is a large push-pull output transformer for valve amplifiers using high plate voltage and high primary impedance. Depending on the secondary arrangement, it provides approximately 6.5, 11 or 23 kΩ plate-to-plate.

The push-pull version provides approximately 570 H of primary inductance and uses a 25 µm balancing air gap. This small gap increases tolerance of minor quiescent-current imbalance but does not replace valve matching.

Suitable applications

• Push-pull output stages using 211, 845 or related high-voltage triodes
• Balanced 300B or other triode stages requiring a suitable plate-to-plate load
• High-impedance pentode or beam-tetrode output stages
• Plate-to-plate loads of 6.5, 11 or 23 kΩ
• 4, 8 and 16 Ω loudspeakers using the documented secondary arrangements
• Class A and Class AB1 stages with controlled quiescent-current balance

Technical data

Product type

High-voltage push-pull valve output transformer

Model version

LL9202/PP

Primary impedances

Approx. 6.5, 11 or 23 kΩ plate-to-plate 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

Push-pull balancing air gap

Approx. 25 µm

Primary inductance

Approx. 570 H

Primary DC resistance

Approx. 600 Ω with all primary sections in series

DC resistance per primary section

Approx. 150 Ω

Secondary DC resistance

Approx. 0.4 Ω average per secondary section

Primary leakage inductance

Approx. 20 mH

Thermal primary-current figure

110 mA according to the 7 W winding-loss criterion; not a permitted DC imbalance

Permitted DC imbalance

No universal numerical value is stated by the manufacturer

Maximum primary signal voltage

Approx. 1,180 V RMS at 30 Hz in push-pull operation

Magnetic power limit at 23 kΩ

Approx. 62 W at 30 Hz

Magnetic power limit at 11 kΩ

Approx. 125 W at 30 Hz

Magnetic power limit at 6.5 kΩ

Approx. 250 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/PP 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-to-plate

8 Ω using secondary Alternative B or 16 Ω using Alternative C

11 kΩ plate-to-plate

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

6.5 kΩ plate-to-plate

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

Ultralinear or CFB taps

Not documented as special features of the standard LL9202/PP

Selection by valves and operating class

The appropriate primary load follows from the valve type, number of output valves, plate and where applicable screen voltage, quiescent current, operating class and intended output.

A 23 kΩ plate-to-plate load requires particularly large voltage swing and suits only correspondingly high-impedance stages. A 6.5 kΩ load tends towards greater current and output but places greater stress on the valves.

In Class A, each output valve ideally sees approximately one-half of the complete plate-to-plate load. At the Class B limit, each valve sees approximately one-quarter during its conducting half-cycle.

Quiescent-current balance

The 25 µm gap is intended to tolerate a small DC imbalance. The quiescent currents of both output valves or valve groups should still match as closely as practical.

The 110 mA thermal figure is not a permitted maximum differential current. Parallel push-pull stages require individual current monitoring, suitable grid stoppers and controlled bias for every valve.

Power and safety notes

The 30 Hz power figures are magnetic transformer limits. Actual amplifier output is limited by the valves, power supply, driver stage, operating class, feedback, cooling and permitted dissipation.

The 1,180 V RMS primary signal capability and typical supply voltages of the intended amplifiers are immediately lethal. Install the transformer in a closed enclosure with adequate electrical clearances.

Questions about selection and use

Which push-pull output transformer suits a high-voltage valve stage requiring 11 or 23 kΩ plate-to-plate?

Lundahl LL9202/PP provides 11 and 23 kΩ plate-to-plate loads for correctly designed high-voltage push-pull stages. The valve, plate voltage, quiescent current, driver voltage and intended output determine the appropriate load.

Which Lundahl push-pull transformer provides 6.5, 11 and 23 kΩ together with up to 1,180 V RMS signal capability?

Lundahl LL9202/PP provides these three primary loads, approximately 570 H of primary inductance and a documented primary signal limit of 1,180 V RMS at 30 Hz.

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

Yes, the LL9202/PP provides suitable secondary arrangements 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.

Is the 25 µm air gap intended to tolerate a small quiescent-current imbalance?

Yes, the 25 µm balancing gap increases tolerance of minor DC imbalance. As Lundahl does not state a universal maximum differential current, valve matching and bias verification remain necessary.