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
There’s currently a lot of interest in creating small amplifiers – just 1-2W output. These typically use dual triodes as the output valve: 12AU7, 12BH7, ECC99, etc. This output transformer is designed for just these projects. Just like its bigger brothers, it’s made in England.
Of course, the current and flux requirements are much lower and so the transformer can be tiny, too. Together with the 240V/6.3V toroidal transformer, it’s perfect for creating a super-compact amplifier. It has clamp-type mounting and comes with a push-fit insulation sleeves to make sure the high-voltage primary solder lugs are touch-proof.
Dimensions & info
This output transformer is just 46mm wide, 40mm deep and 36mm tall. Fixing centres for the U-clamp mounting feet are 56mm apart. Typical bandwidth is 85Hz – 6kHz. Its output impedance is 22,500 ohms and it has both 8 or 16 ohms outputs for speakers. Note the solder lug positions shown in the diagram on the right: the speaker outputs are uppermost and the primary winding is on the bottom set of lugs.
If your amp build is such that there’s a risk of someone inadvertently touching the secondary solder lugs, you must use the slide-on insulating sleeve. Of course, the transformer is so small that you can mount it inside most chassis, and if you do that, you don’t need to use the sleeve. This 4W output transformer is tiny – I’ve included a £1 and 1euro coin for scale in the photo. This makes it easy to build into your chassis, if necessary.