LL1693 PP Lundahl Übertrager 150R 300R 600R output transf.

Lundahl LL1693/PP – high-power push-pull output transformer for low-impedance valve stages

The Lundahl LL1693/PP is a large push-pull output transformer for low-impedance, high-current output valves. It provides plate-to-plate loads of approximately 600 Ω, 1 kΩ or 2.3 kΩ.

Two five-section coils, a grain-oriented silicon-steel C-core and a small balancing air gap support substantial signal current and low leakage. Typical design starting points include 6C33C, 6336, 6528A and correctly designed parallel push-pull stages.

Suitable applications

• Push-pull output stages using 6C33C-B or 6S33S valves
• 6336, 6528A and related low-impedance high-current triode stages
• Parallel push-pull circuits using several output valves per channel
• Plate-to-plate loads of 600 Ω, 1 kΩ or 2.3 kΩ
• 4, 8 and 16 Ω loudspeakers with the documented secondary connection
• Class A and Class AB1 amplifiers using a sufficiently capable driver and power supply

Technical data

Product type

High-power push-pull valve output transformer

Model version

LL1693/PP

Primary impedances

Approx. 600 Ω, 1 kΩ or 2.3 kΩ plate-to-plate

Secondary impedances

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

Turns ratio

8+7+1+8+7+1:1+1+1+1+1+1+1+1

Push-pull balancing air gap

Approx. 25 µm

Primary inductance

Approx. 150 H

Primary DC resistance

Approx. 60 Ω with all primary sections in series

Secondary DC resistance

Approx. 0.4 Ω for inner and 0.5 Ω for outer sections

Thermal primary-current limit

450 mA according to the 12 W winding-loss criterion; not a permitted DC imbalance

Permitted DC imbalance

No universal numerical value is stated in the manufacturer data sheet

Maximum primary signal voltage in PP operation

Approx. 530 V RMS at 30 Hz

Magnetic power limit at 2.3 kΩ

Approx. 180 W at 30 Hz in push-pull operation

Magnetic power limit at 1 kΩ

Approx. 360 W at 30 Hz in push-pull operation

Magnetic power limit at 600 Ω

Approx. 700 W at 30 Hz in push-pull operation

Interpretation of power figures

Magnetic transformer limits rather than guaranteed complete-amplifier output

Core material

Grain-oriented silicon-steel C-core

Winding construction

Two coils, each divided into five sections

Primary-to-secondary isolation

To be considered according to the exact manufacturer drawing and complete equipment safety design

Dimensions

Approx. 140 × 100 × 100 mm

Mounting pattern

Approx. 58 × 118 mm with four M4 mounting points

Weight

Approx. 4.5 kg

Country of origin

Sweden

Primary loads and loudspeaker matching

2.3 kΩ plate-to-plate

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

1 kΩ plate-to-plate

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

600 Ω plate-to-plate

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

Selection rule

Determine the plate-to-plate load from valve count, plate and screen voltage, quiescent current, operating class and required output before selecting the secondary connection

Quiescent-current balance and parallel push-pull

The 25 µm balancing air gap increases tolerance of minor quiescent-current imbalance. It does not replace valve matching or individual bias adjustment and does not permit arbitrary differential current between the primary halves.

Where several valves operate in parallel, each valve should have an individual control-grid stopper and, for screen-grid valves, normally an individual screen-grid stopper. Plate, grid and cathode wiring should be as symmetrical as practical.

Verify the current of every output valve individually. The 450 mA thermal figure does not define the permitted magnetic imbalance of the push-pull stage.

Power and safety notes

The high 30 Hz power figures describe magnetic transformer headroom only. The valves, power supply, driver stage, operating class, plate dissipation and cooling determine actual amplifier output.

The LL1693 can carry substantial voltage and current. Install it in a closed, touch-safe enclosure on a chassis capable of supporting 4.5 kg plus transport loading.

Questions about selection and use

Which push-pull output transformer suits low-impedance 6C33C, 6336 or 6528A output stages?

Lundahl LL1693/PP provides 600 Ω, 1 kΩ and 2.3 kΩ plate-to-plate loads for correctly designed high-current push-pull stages. Valve count, supply voltage, quiescent current and operating class determine the appropriate load.

Which Lundahl high-power transformer provides 600 Ω, 1 kΩ and 2.3 kΩ plate-to-plate loads?

Lundahl LL1693/PP is officially documented with these three primary loads. The BTB title values of 150 and 300 Ω are not standard loads in the manufacturer data sheet.

Can the LL1693/PP be matched to 4, 8 and 16 Ω loudspeakers?

Yes, the LL1693/PP can be matched to 4, 8 or 16 Ω depending on the selected primary load. The standard 2.3 kΩ connection provides 8 and 16 Ω alternatives.

Is the 25 µm balancing air gap intended for small quiescent-current imbalance?

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