How are Lundahl output transformers wired?

With most Lundahl output transformers, there is no way around the data sheets, as most types offer several connection options and therefore a larger number of transformation ratios. This allows the windings to be used as effectively as possible and improves coupling. The data sheets can be found from the manufacturer or in the BTB Elektronik online shop under Downloads for the respective product. Please note that both sides, meaning the primary side and the secondary side, must always be wired. In many cases, bridges also have to be soldered according to the diagrams.

The star in the circle in the data sheet always marks the beginning of the winding and is therefore important for polarity, meaning the phase position. V+ is the transformer input on the primary side, coming from the power supply. Tube Anode is the anode connection. The secondary connection is usually optimized for a specific load impedance.

For example, if you look at the data sheet for the Lundahl LL1620, LL1623, LL1627 or LL902, you will find a three-column table. Depending on the desired primary impedance (Ra or Raa), the secondary side is then wired accordingly, for example B/C/D for 4 Ω / 8 Ω / 16 Ω or C/D/E for 4 Ω / 8 Ω / 16 Ω.

Example 1:

Single-ended operation with Ra = 3 kΩ and Rl = 8 Ω, selected transformer LL1623 (90 mA), then the following applies:

“Primary Connections”: right column, lower diagram
“Secondary Connections”, meaning secondary: middle row, left diagram (C)

Example 2:

Push-pull operation with Raa = 3.3 kΩ and Rl = 8 Ω, selected transformer LL1620 (PP), then the following applies:

“Primary Connections”: diagram at the top far left
“Secondary Connections”, meaning secondary: middle row, right diagram (D)

Tip: If oscillation or whistling occurs in push-pull circuits, it may be necessary to swap the two anode connections and, if necessary, G2 as well.