RFT Minirex 75

---

The electron tube factory in Mühlhausen (VEB Röhrenwerk Mühlhausen) in addition to produce vacuum tubes, started manufacturing semiconductor diodes in 1971, and planned to apply microelectronics in products. Around 1972 made possible to assemble pocket calculators with some american parts, so the first series, Minirex 73 was launched in 1973. In addition to AMI-made calculator chip, it contains a lot of domestic integrated circuits and passive elements too. The next model, the Minirex 74 used algebraic logic, which was supported by the AMI chip, so this version missed the constant switch. In this model appeared first the GDR-made U821 series IC, which was a functional copy of the AMI circuit. Interestingly, the Minirex 75 introduced in 1975 used original Texas Instruments TMS0105 circuit instead of GDR-made U820, and therefore it used arithmetic logic again, but it has a new decimal switch. After the huge and heavy Minirex-series, partially with soviet parts a really pocket-sized calculator-series was launched in 1975, with starting mass production of Konkret 100 and 200 models first.