For inexpensive general purpose single ended use, Hammond 125SE series is hard to beat. 125CSE is rated 8W and 60mA. Primary is configurable from 2.5K to 10K ohms, secondary from 4 to 32 ohms. This is THE transformer for smaller guitar amps, and is also an excellent choice for entry-level SE audio amp designs. Weighs 1.5lb

Designed for push-pull tube output circuits.

30W, Primary 5K with center tap. Max 128mA DC per tube. Secondary 4-8-16 ohms, and 70V load.

Shielded, 4 slot, above chassis Type "X" mounting. 30 Hz to 30 Khz at full rated power. 40% screen taps for Ultra-Linear operation. 4.5lb

For connection, see manufacturer's page.

UBT-3 is an output transformer with 3K primary and 16/8/4 ohms secondary. It is designed to be used in a single ended output configuration in HiFi Audio application. Similar to Hammond 1627SE but with lower rating (15W) and with half the weight. And we like the sound of this transformer a little better.