From 1901 to 1916, there was no separate workshop in Sofia, and the tram maintenance, repair and service included only replacement of ready-made spare parts, which was accomplished in the depot. The only depot at that time called Maria Luisa had the following machines: type lathe, hydraulic press, band saw, wood cutting circular saw, planer, shaper, three small drills, and a small wood-turning lathe.

The increased need for better technical support and repair of the rolling stock called for the organization of a separate workshop.

From 1927 the trams are under the control of Sofia Municipality, and a Main Technical Workshop was established and equipped on the territory of Maria Luisa Depot. It was expanded for that purpose, and special departments of the workshop were organized: tool, locksmith, lathe, fitting, smithing, winding, spaying and painting, sheet metal work, harness making, foundry, shooting departments, etc.

In 1927, the enterprise for repair, refurbishment and reorganization of power cars and trailing units was established.

From 1927 to 1931, discarded trailing units were refurbished in the tram workshop, and 20 of them were reconstructed from winter into summer ones. The braking mechanisms were repaired in the same period, and all trams were put into working order.

In 1931, the first in the country electric arc furnace for steel melting was delivered and installed in the foundry of the technical workshop.
At the end of the same year the tram company possessed a solid (for that time) workshop, serving as a base for future tram repair and production.

Eng. Kardalev, the first manager of the technical workshop, contributed a lot to this great technical progress of the company, and especially of the technical workshop. According to his proposal and under his supervision the first 12 winter and summer trailers (№ 501-512) were built from discarded car chassis, and in the period from 1934 to 1935, 12 entirely new trailers (№ 301-312) provided with a hand brake were manufactured in the workshop for the first time.

The Bulgarian tram construction in the Main Technical Workshop began in 1936 with the construction of the first Bulgarian two-axle trams, with inventory numbers from 41 to 46. They were produced from existing tram chassis, and their motors and controllers were delivered by Breda-Ansaldo Mareilli.

20 trailers (№351 - №370) with hand and electric brake, rivet chassis and wooden bodywork were built from 1937 to 1938.

In 1939 – 1940, 7 new power cars with separate bogies (welded construction) were built with imported controllers and motors. These were with hand and electric brake.

From 1941 to 1943, 12 trailers with hand and air-operated brake, and 2 power cars (№32 и №33) were produced. The electric motor housings of these trams were casted and processed in the workshop.
The construction of a new depot became a necessity with the increase of the rolling stock. Krasno Selo Depot was the second tram depot in Sofia. The modern for its time bright and spacious building with fanlight was built in 1934.

The tram workshop in Maria Luisa Depot was quite damaged by the bombings in 1943-1944, and the machines were evacuated to Vladaya and to Krasno Selo Depot.

After the war, the evacuated to Vladaya machines were moved and mounted in Krasno Selo Depot, and it became the Main Technical Workshop, providing repair and refurbishment of the badly damaged by the bombings power cars and trailers.

After extension and reorganization, the newly equipped Main Technical Workshop of Tram and Lighting Department started producing power cars and trailers once again in 1947. In the meantime, the workshop was equipped with new machines (lathes, shaping machines, horizontal shapers, milling machines, air hammer, etc.)

Based on the design of Eng. Y. Yordanov, in 1951, began the production of power cars of the Republika type, with hand and air-operated brake systems (direct brake control), while the electromotors, controllers, motor-compressor unit and main switch were made in Bulgaria.

The first Bulgarian trolleybus ТБ-51 (on the Russian model МТБ-82) was built the same year.

At the end of 1951, the technical workshop became a separate factory called September 6th for construction and repair of tram power cars, trailers and trolleybuses, as well as for production of city bus bodyworks.

In 1959 the new production of trams and trolleybuses was separated from September 6th factory and transferred to Public Passenger Transport Company, and the Main Technical Workshop for Tram Repair and Production was formed again.

In the period 1959 – 1963, 15 power cars of new generation, called Komsomoletz, and 16 four-axle trailers for these cars were produced. These power cars were 14 m long, equipped with four traction motors for a drive output of 50kW. The higher installed power allowed the power cars to climb steep gradients, and move at speed of 60 – 65 km/h.

For the first time in this series, power cars with rubber cushions between the road wheel tires and hubs were put into operation in Bulgaria. This led to less wear of the rail system and tires, and less noise by motion. Special rubber cushions were put also under the bogie springs for the same purpose.

The first articulated six-axle tram Kosmonavt was produced in 1961. Its bodywork was formed by linking two sections, which increased the tram size significantly, and made it very comfortable for the passengers. 63 trams of this series were constructed.

In order to increase the exploitation and technical qualities of the articulated trams, a prototype with an inventory number 963, new bogies and Kosmonavt bodywork was produced in 1964. The mass production of trams, model called Sofia, № 801, 20 m long started on this basis.

Later on the double-articulated tram Sofia-70 was produced with this construction used as a base. It differed from №801 by its considerable length - 26 430 mm, and a new construction – passenger seats.
In 1964, the company was transformed into Branch 4 – Production and Repair of Trams and Trolleybuses of the Public Passenger Transport Company.
In 1969, a new hydraulic press for wheelsets, which replaced the existed water press, was installed and put into operation.

At the beginning of 1976, the company was renamed to Sofia Tram Factory.

In the eighties, a number of specialized machines and equipment aiming better work quality and organization were imported and installed – Rafamet wheelset lathe– 1984, Hiteka impregnation system, digitally controlled machine tools. After the production of Sofia – 100 and Bulgaria 1300 trams, which do not differ from Sofia trams except for the body, Sofia Tram Factory started the production of new types of trams.

The first Bulgarian tram with cardan shaft drive - type Т6М-700 (Inv. №701) was produced in 1986. In the following year, a tram for track of 1435 mm (type Т6МД-1000) was produced on the basis of this construction.
At the beginning of the nineties, the production of Bulgarian trams was suspended. The last Bulgarian tram was manufactured in May 1991 in TRAMCAR Company – the new name of the factory since 1990.
1 trolleybus (ТК-130) with electronic control of contactors was produced in 1994, and was put in regular operation in 1997.

The main tendency in TRAMCAR activity between 1997 and 2001 was the modernization of the tram rolling stock applied to existing trams of Т6М 700М series. The main characteristics of modernization were, as follows:

- Reliability increase and operational expenditures decrease
- New reductor
- New axle box suspension
- Better connection body - bogie and new central spring suspension
- Bodywork arch reinforcement of new and old bodies
- Traffic safety increase
- Brakes at low rpm
- Static transformer installation
- Additional sandboxes in front of the 7th wheelset
- Vigilance system
- Switch-off device for the additional consumers by activation of automatic switches
- Better travelling comfort
- New design and impressive coloring
- New modern interior
- Anti-slippery sheet
- New comfortable ergonomic seats
- Colored trailer windows
- Tubular structure with plastic covering
- Lighting and heating with considerably better characteristics and reliability
- Illuminated front, back and side registration plates
- Better comfort for the driver
- New functional tram driver seat
- New control panel
- Cabin heating and ventilation through windshield outlets

Except for the above mentioned main characteristics of modernization, the trams of series Т6М - 700М were also extended (from two-section to three-section units) by mounting of a new middle module. Thus the tram carrying capacity was increased.

In order to preserve unique old trams and trailers, TRAMCAR JSC restored a MAN - Siemens – 1935 tram in 1999, and constructed a DTO - KARDALEV 1928 trailer on an authentic running gear in 2000, according to preserved documents.

In May 2000, a tram for two-way motion was manufactured in TRAMCAR. It is used by track repair works for servicing passengers on one track (in two directions).
In 2002, one of the trams for 1435 mm gauge was upgraded from Т-81 to Т-86 bogie with electrical equipment developed by ALSTOM, Czech Republic.

The reorganization of Cobra high-floor bus into a trolleybus started in 2002.

In 2005, two Cobra buses with partially low floors were reconstructed into trolleybuses in the Tramcar Company using electrical equipment imported from Romania.
The last modernized tram of 900Н series was put into operation in 2007.

In 2006, the Tramcar Company entered into a contract with the Czech company INEKON as a subcontractor for modernization of 18 trams of Т6М-700 series – the first one was put into operation at the beginning of 2008.

At the end of 2008, Tramcar signed a contract for major repairs and partially modernization of 9 trams, Т6М-700.

Except for the above specified new products of Tramcar, repairs of all types of trams, Icarus trolleybuses, bogies, wheelsets, and motors were conducted, and 74 electronic tram stop signs, ticket kiosks and three funeral trains with trailers were also constructed.

In November 2008, TRAMCAR JSC joined Sofia Public Electrical Transport Company JSC, and was reorganized into a Tramcar Department retaining its scope of activities.