Lundahl
power transformers




All Lundahl C-core mains transformers use a very small air-gap is used to compensate for any DC unbalance in the mains outlet.

Secondary voltages listed are no-load voltages. Voltage drop because of load is to be calculated from transformer copper resistance and load current. Electrical size is estimated to 250VA, which can be increased with good cooling. For optimal use, about 75% of power should be taken from secondary 1.

Primaries should be connected in series for 210 - 250 V, in parallel for 105 - 125V. Table entries are calculated for primary voltage 230 V.


Power transformers
               
Type Sec. 1 Sec. 2 Sec. 3 Sec. 4 Sec. 5 Sec 6. Sec. 7
Weight (Kg)
               
LL1648 350V / 0.63A 5.9V / 3.1A 5.9 / 3.1A 6.6V / 3.1A 6.6V / 3.1A    
2.5
LL1649 230V / 1.0A 6.6V / 3.1A 6.6V / 3.1A 6.6V / 3.1A 6.6V / 3.1A    
2.5
LL1650 350V / 0.63A 6.6V / 3.1A 6.6V / 3.1A 6.6V / 3.1A 6.6V / 3.1A    
2.5
LL1651 500V / 0.43A 6.6V / 3.1A 6.6V / 3.1A 6.6V / 3.1A 6.6V / 3.1A    
2.5
LL1669A 340V / 0.55A 6.3V / 3.1A 6.3V / 3.1A 6.3V / 3.1A 6.3V / 3.1A 110V / 40mA  
2.5
               
LL1683 250V / 80mA 250V / 80mA 48V / 0,1A 6.6V / 3A 6.6V / 3A 5.2V / 3A 5.2V / 3A
1.4
               

Filament transformers
               
Type Sec. 1 Sec. 2 Sec. 3 Sec. 4 Sec. 5 Sec 6. Sec. 7
Weight (Kg)
               
LL2738 110V / 0.1A 8 X filament winding. Each winding 6.6V / 3A. (will drop to 6.3V at 3A current)
2.5


Mains Isolation transformers
These mains transformers are for isolation and DC current elimination. The core is assembled with a carefully selected, very small air-gap to compensate for any mains DC-unbalance. Power rating can be increased with good cooling.
               
Type Estimated power         .  
Weight (Kg)
               
LL1655 300VA            
2.5
LL1658 100VA            
1.4
LL1662 300VA Mains isolation transformer with step-up / step-down options
2.5
               

 



Tube Amplifier Hybrid Power Supply


 The schematics below are based on the Hybrid Graetz Bridge concept after a Fulvio Chiappetta paper, published by the Italian Magazine ‘Costruire HiFi’ a reference for the DIYers. He tested and comparated this topology versus a pure tube vacuum state power supply design with a 300B output tube amplifier and there was no difference both while listening and measuring the output noise spectrum.