T 435.0 (720) and T 458.1 (721) class locomotives with electrical power transfer were popular during their use, and suitable for shunting work. T 444.0 and T 444.1 (735 and 736) with hydraulic power transfer were also used for medium shunting services, but the output of all these locomotives and their mass were not sufficient for heavy shunting at rail yards, and for shunting services in freight transport. This is why after the lack of success of two-generator locomotives, the Ministry of Transport commenced the development of a motor locomotive with 1350 k (880 kW) output in a six-axle version with axle weight rating up to 18 tons. Soviet Railways were also interested in the same locomotive, which is why in 1963 three prototypes were manufactured at CKD Praha – one for normal track gauge, and two for 1520 gauge tracks with central couplings. After prototype testing, the locomotive was purchased for Czechoslovak Railways in 1966. The locomotives had excellent properties, and demand from the former USSR was so high that they fully taxed the capacity of CKD Praha for this class, which led to the handover of series manufacture for CSR to Dubnice nad Vahom, from where they were also supplied between 1967 to 1969.
T 699.0 (770) class locomotives are six-axle, with two bogies. The wheel pairs are set in radius arms and have a simple coil spring suspension. The body is mounted on the frame with eight anchors. 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. Chillers and ventilators are located here as well. TE 006 traction motors are axle-mounted on the wheel sets. Located underneath the rear hood are batteries and a supply of sand. 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. This class of locomotive, manufactured for Czechoslovak State Railways, Soviet Railways, and railways in Poland, Albania, India, Iraq and Syria numbers over 8000 units, making it the largest series of locomotives ever manufactured in the Czechoslovak Republic.
The basic colour of the prototypes for Czechoslovak Railways was light green, which was on the hood and operator's cab. Running around the entire locomotive at window height is a wide, cream-coloured band, widened to a point on the front surfaces of the hoods. Above and below it are narrower bands of the same colour, only in the part running over on the side hood surfaces. The cab roof was also cream-coloured. The locomotive's frame is red (dark vermilion). The undercarriage equipment below the frame, steps, bumpers and couplers are black. The front guards are checked, white and red.
|Original ÈSD series designation||T669.0|
|Current series designation||770|
SMZ Dubnica nad Váhom
|Number produced for ÈSD||111|
|Number in ÈD fleet||74|
|Drive wheel diameter||1050 mm|
|Bumper-to-bumper length||17220 mm|
|Continuous output||880 kW|
|Maximum speed||90 km/h|
|Service weight||112 t|
|Number of traction assemblies||1|