LT44 / P631M transformer

The Eagle P631M transformer (formerly called the LT44) is a 20k:1k CT transformer that is commonly used for audio applications, particularly as an inter-stage push-pull driver. The LT44 first appeared in electronics catalogs in the mid-1960s and was commonly sold at electronic hobbyist shops in the UK. For our purposes, it’s best known as the transformer used in the Lovetone Ring Stinger ring modulator, which uses two of them.

At some point the LT44 came to be sold in two versions, one with blue tape around the windings and one with yellow tape. The blue version had a 20k primary while the yellow version was 10k. The secondary was the same for both. The P631M is the blue version. (The yellow version does not appear to be actively manufactured anymore.) The ones used in the original Ring Stinger were stamped “LT44” on the frame. Current production does not have any part number or marking anywhere, but we’ve tested them in our circuit and found them to sound identical when compared to an original Ring Stinger.

The primary and secondary are not marked, but the primary is the side with only two pins while the secondary has three. Note that the 1k secondary specification is measured from the outsides of the windings, not from the center tap. In other words, it’s a single 1k secondary that can be center-tapped, not two 1k secondaries.

These are imported from Eagle in the United Kingdom and are sold in full retail packaging with bag & header.