18W push pull output transformer

2021 UPDATE: This TX is used in Amp Maker kits and has also been a popular choice for other amp builders. It’s no longer available to buy from Amp Maker, but you can order it directly from the TX maker, Primary Windings Ltd

The latest version of this transformer is a direct clone of the transformer originally made by Danbury (who has since retired). That transformer came from my search for an output transformer for my PP-18 amp kit (a stripped-down version of the classic Marshall 18W amp of the ’60s). There were some British OTs available off-the-shelf (supposedly made for Marshall in recent years), but they seem designed down to a size – as if to fit into a 1U rack mount box – and they didn’t sound very good when the amp was pushed.

There were also several higher-cost US-made OTs for the 18Wer, including the Heyboer, which I liked (except for the cost of shipping and importing). We started by taking that Heyboer apart and making several variations on the theme. After a tone test, I settled on the best-sounding version (which happens to have grain-oriented laminations). It’s designed for use in a typical 2 x EL84 valve power amp, but would work fine in any push-pull output stage of 15-20W that requires an 8k ohms primary impedance. It has 8 and 16 ohm speaker taps. It’s clamp-mounting, with flying leads for connections.

Dimensions & info

Wound by a British company that also makes some of Amp Maker’s other transformers, this output transformer is 78mm wide, 64mm deep and 64mm tall. Fixing centres for the U-clamp mounting feet are 96mm apart. A great-sounding output transformer for classic 18W-based amplifiers Wire colour coding shown (right).