T-669.0 (770) class diesel locomotives, built by ČKD are six-axle, with two bogies.

The wheel pairs are set in radius arms and have a simple coil spring suspension.

The locomotive is a hood unit type with an internal, eccentrically positioned operator's cab.

Located underneath the front hood is the traction assembly – a K 6 S 310 DR diesel engine and a TD 802 traction generator – and auxiliary machinery powered by the diesel engine via a hydrodynamic transmission.

After modifications of the seating of the hood on the frame, the T 669.1 (771) and the wide-gauge version T 669.5 (770.8) were created at SMZ Dubnica.