I have only discovered relatively recently that Bulgaria has a significant semiconductor industry, dating from 1964, which made both germanium and silicon devices and employed more than 29,500 people. There is some information on the Web but it does not include the earliest period and gives the impression that only silicon types were made from the 1970s onwards. That is incorrect. I am grateful to Konstantin Konstantinov, who spent his whole working life in this industry, for most of the information below.

The manufacturing facility was called the 'Semiconductor Instrumentation Plant (SIP)' located in Botevgrad. It was built over 19 months by the company 'Zavodski stroegi' from Vratsa region. The first workers in the main facility started on 23.12.1963, the majority of them undergoing a 30 day training course at the CSF plant in Grenoble, France, the plant having obtained a licence from COSEM to make SFD and SFT series devices. In September 1964, the point diode production line was launched. On November 13, 1964 the first sale of diodes and transistors was made. Rather belatedly, on April 28, 1965, Todor Zhivkov officially cut the tape of the Semiconductor Plant.

The plant was expanded in 1965 - 1973 into four main production lines: germanium, planar-epitaxial, silo-silicon and MOS integrated circuits. Each of the productions is divided into four workshops: 'Transistors', 'Semi-finished products', 'Glassmetal' and 'Diodes', because of technological specialization and to streamline production process organization. It has produced devices for the GDR, the USSR, Poland, Czechoslovakia, Romania, North Korea and some Western European countries. On 11 January 1982 the first sod was cut for the extension of the Integrated Circuit Plant. In 1986 this grew into the 'Microelectronics' plant which still exists.

I have little data (original or copies) for Bulgarian germanium semiconductor devices. However, searching for it led me to an interesting document: 'Translations on Eastern Europe Scientific Affairs No 569', (largish pdf!) dated 12 January 1978. This contains the article 'SEMICONDUCTOR DESIGNATION SYSTEMS DESCRIBED' which does indeed describe the part numbering systems used for Eastern European semiconductors, one standard for Bulgaria, several for the Soviet Union, and one for Czechoslovakia, plus the JEDEC, Pro-Electron, Japanese and British CV schemes.

The Bulgarian scheme is apparently documented in Bulgarian State Standard 9840-72, but I have not been able to locate a copy of this on the Web. The translation describes it briefly, and it is relatively simple (and very similar to one of the USSR schemes):

If you can tell me more about early Bulgarian transistors and diodes, please

SFT124 transistor

The first germanium devices produced in the SIP follow the French naming convention SFD for diodes and SFT for transistors, but with the difference from the originals that there is no period after SF (SF.T in CSF/COSEM types). My image shows an SFT124 without the period, a germanium PNP medium power audio frequency amplifier. My page on French transistors shows a similar SF.T125 with the period.

GT1321 transistor

This is a Bulgarian germanium transistor, type GT1-321 (the hyphen is optional, the GT is Cyrillic). It is a germanium PNP type.

GT4131 transistor

This is a GT4-131, which I am informed is equivalent to the COSEM type SF.T131, a germanium PNP medium power audio frequency amplifier. I do not know why such equivalent devices were made. If you know about it, please

GT7312 transistor

I have one Bulgarian germanium power transistor, this GT7-312. The 1978 translation described above gives the GT7-312 (blue dot) as an example of a 'germanium transistor, power, low-frequency, gain 54-80 units'. My GT7-312 has a yellow dot (rather dark in the image). I have come across a Romanian electronics forum article that lists the different gain ranges per colour:

There is obviously a lot of overlap in these bands, which is puzzling.

wanted transistor

I am interested in finding other Bulgarian germanium transistors and diodes. If you can help me, or tell me more about early Bulgarian transistors and diodes, please