Between 1961 and 1965, Bulgaria faced a problem with the unsifficiency of traction rolling stock for meeting the increased traffic rates. In 1963, test trips with a 600 HP engine of the Austrian railways were carried out on the line between Septemvri and Yakoruda. The purpose was to find out which was the best type of new rolling stock for 760 mm gauge. This power proved unsufficient and it was decided that engines with 1100 HP will be bought instead. These were the most powerful locomotives for 760 mm gauge in the world by that time. Their designed speed was 70 km/h. In 1965-1966, the German company „Henschel“ — Kassel delivered 10 diesel-hydraulic narrow gauge locomotives of the series 75.00. They were manufactured in 1965 specially for the line Septemvri-Dobrinishte. After the delivery, they overtook the complete passenger and freight service on the stretches Septemvri-Dobrinishte and Pazardzhik-Varvara, replacing the diesel railcars series 81 and 82 on long distance passenger trains and the steam engines of the series 600.76 on freight trains. Fast passenger trains appeared for the first time in the timetable of 1966. They did not stop at stops and some of the smaller stations, thus reducing travel duration by one hour in comparisson to steam engines. The locomotives in operation of this series nowadays are 75 004.2, 75 005.9 and 75 008.3, temporarily isolated are 75 002.6 and 75 009.1, 75 006.7 is undergoing a general overhaul, and 75 010.9 is being stored at the Septemvri railyard for spare parts.
Produced under license of Maybach-Mercedes
A delivery of additional narrow-gauge diesel locomotives for the line Septemvri-Dobrinishte was considered in 1973. Due to the double price „Henschel“ — Kassel required and the order to limit commercial contacts with „capitalistic countries“ for political reasons, the delivery of the new diesel locomotives had to be made from Romania. The machines were manufactured at the „23 avgust“ factory in Bucarest. They were produced under license of Maybach-Mercedes. A contract for the delivery of 15 diesel-hydraulic locomotives with the traction formula B’-B’ was made. On the 7th of November 1976 a prototype locomotive was delivered to BDZ for making several test trips. It was then sent back to Romania for further improvements. The delivery of the first five engines of the new series 76 for the line Septemvri – Dobrinishte was made in 1977-1978. It was ensured that the two series had as many similarities as possible in design and performance. The new series perform significantly worse in comparison with the German 75 in terms of capacity, maintainability, failure of individual aggregates and production quality. After the closure of the line Cherven bryag – Oryahovo in December 2002, thelocomotives were transfered to the line Septemvri – Dobrinishte. Part of them still remain out of service and in 2009 BDZ sells four more locomotives of the series 76 to Argentina (76 005, 76 006, 76 011, 76 012). At the moment only one engine of this series is being stored for spare parts in the yard of the locomotive depot in Septemvri – Number 76
In 1988, 10 units were delivered
10 diesel-hydraulic locomotives from the Romanian factory „23 august“ in Bucarest werde delivered in 1988. They were built after the technical requirements of the Bulgarian State Railways and were given the new series 77, wich was to mark the numerous improvements in comparison to 76. With their delivery, the complete service across Bulgaria’s narrow-gauge lines was secured for the years to come. All machines were enrolled in the locomotive depot in Septemvri and were heavily used during their warranty period. Due to the decrease in passenger and above all freight traffic after 1990, many of the locomotives came out of service. In 1996, BDZ sold five of them (77 001.6, 77 003.2, 77 004.0, 77 007.3 и 77 010.7) to the company „Yacimientos Carboníferos Río Turbio“, which operates the coal mines in Rio Turbio, Argentina. There they served the 200 kilometres long 750 mm-gauged track from the mines to the Rio Galegos port. To this day, in regular service on the line Septemvri – Dobrinishte are 77 002.4 and 77 009.9, while 77 005.7 and 77 008.1 are in temporary isolation at Septemvri engine depot.
Видео от атракционно пътуване с локомотив 609.76 през октомври 2015 г. Автор: Николай Вичев