LL1683 Lundahl Netztrafo 120VA 2x250V 80mA 48V 6,6V 5,2V

Lundahl LL1683 – 120 VA C-core mains transformer with flexible heater and high-voltage windings

The Lundahl LL1683 is a C-core mains transformer for valve amplifiers with two separate 250 V/80 mA high-voltage windings. They can feed a centre-tapped valve rectifier or be connected in phase and in parallel for bridge rectification.

Additional windings provide 48 V, two separate 6.6 V/3 A heater supplies and two separate 5.2 V/3 A rectifier-heater supplies. All listed secondary voltages are no-load values and fall under load according to mains voltage, winding resistance and current.

Suitable applications

• Valve-amplifier power supplies using 250-0-250 V full-wave rectification
• Bridge rectification from two parallel 250 V windings
• Preamplifiers and power amplifiers requiring several isolated heater circuits
• 5 V rectifier valves using suitably loaded 5.2 V windings
• 6.3 V valve heaters supplied from the 6.6 V no-load windings
• Bias, relay, regulator or auxiliary circuits using the 48 V winding

Technical data

Product type

C-core mains transformer for valve amplifiers

Model

LL1683

Estimated total rating

Approx. 120 VA; use this as the complete power budget for all windings

Primary connection for 230 V

Two 115 V primary windings connected in phase and in series

Primary connection for 115 V

Two 115 V primary windings connected in phase and in parallel

Primary DC resistance in series

Approx. 7.5 Ω

Primary DC resistance in parallel

Approx. 1.9 Ω

High-voltage secondary Sec 1

250 V AC no-load, 80 mA maximum recommended RMS current and approximately 100 Ω resistance

High-voltage secondary Sec 2

250 V AC no-load, 80 mA maximum recommended RMS current and approximately 100 Ω resistance

Auxiliary winding

48 V AC at 0.1 A with approximately 40 Ω resistance

Heater winding 1

6.6 V AC no-load at 3 A with approximately 0.2 Ω resistance

Heater winding 2

6.6 V AC no-load at 3 A with approximately 0.2 Ω resistance

Rectifier-heater winding 1

5.2 V AC no-load at 3 A with approximately 0.2 Ω resistance

Rectifier-heater winding 2

5.2 V AC no-load at 3 A with approximately 0.2 Ω resistance

Calculated sum of individual winding ratings

Approx. 115.6 VA; additional thermal and mains-voltage margin remains necessary

Rectifier guidance with capacitor input

Manufacturer guidance: approximately 63% of the applicable AC RMS current as DC output

Rectifier guidance with choke input

Manufacturer guidance: approximately 95% of the applicable AC RMS current as DC output

Core

Lundahl C-core with a small balancing gap to compensate for mains DC imbalance

Magnetic stray field

Particularly low when heater windings on both coils are loaded as equally as practical

Dimensions

Approx. 98 × 78 × 65 mm

Mounting pattern

Approx. 35 × 75 mm with four M4 mounting points

Weight

Approx. 1.4 kg

Country of origin

Sweden

Primary and high-voltage connections

230 V primary connection

Join pin 4 to pin 10 and apply mains between pins 2 and 12

115 V primary connection

Join pins 2 and 12 together and join pins 4 and 10 together with the correct phase

250-0-250 V full-wave connection

Use pins 15 and 17 as the outer ends and joined pins 22 and 24 as the centre tap

250 V bridge connection

Connect the two high-voltage windings in phase and in parallel; the manufacturer drawing joins pins 15 and 24 and joins pins 22 and 17

Important connection principle

Implement the complete rectifier and choke topology exactly in accordance with the Lundahl drawing

Power budgeting and heater voltages

Do not add winding ratings beyond the 120 VA total. Fully loading both 6.6 V and both 5.2 V windings uses approximately 70.8 VA, leaving correspondingly less capacity for the high-voltage and auxiliary windings.

The 6.6 and 5.2 V figures are no-load voltages. Measure actual heater voltage with the valves connected and at the real mains voltage. Excessive heater voltage reduces valve service life.

Capacitor-input supplies produce substantial charging-current peaks. Rectifiers, fuses, first filter capacitance and inrush limiting must suit the complete circuit.

Safety and installation notes

Mains voltage and the high-voltage secondary are immediately lethal. Provide suitable primary fusing, double-pole isolation, protective earth, strain relief and complete touch protection.

Mount the mains transformer with suitable distance and core orientation relative to sensitive input transformers, phono stages and output transformers.

Questions about selection and use

Is the Lundahl LL1683 suitable for a valve supply using 250-0-250 V and a tube rectifier?

Yes, the Lundahl LL1683 has two separate 250 V/80 mA windings that can form a centre-tapped 250-0-250 V secondary. The rectifier current, filtering and complete 120 VA power budget must suit the circuit.

Can the LL1683 operate with a bridge rectifier?

Yes, the LL1683 can feed a bridge rectifier with its two 250 V windings connected in phase and in parallel. Winding phase, rectifier current, inrush current and total power loading must be considered.

Is the LL1683 suitable for separate valve-heater circuits and a 48 V auxiliary supply?

Yes, the LL1683 provides two separate 6.6 V/3 A windings, two separate 5.2 V/3 A windings and a 48 V/0.1 A auxiliary winding. Verify the actual voltages under the connected load.