Tube equipped receivers from Siemens
Since the late 19th century, the German company Siemens has been active in all areas of electricity and telecommunications. The company was founded in 1847 as Telegraphen-Bau-Anstalt Siemens & Halske and was already active in the early days of radio technology in the construction of transmitters, receivers and also in tube production. Radio production came to a standstill with the destruction of the Siemens factories in Berlin and Arnstadt due to World War II.
After the end of the Second World War, Siemens resumed its own receiver production and supplied mainly the navy with powerful receivers. The E 309a was followed by the E 310a in 1961, the bulky receiver with the large arc-shaped dial, the different ranges were coloured and activated with correspondingly coloured keys, got it's name as rainbow receiver and performed well especially in the VLF ranges; the 1 kHz dial accuracy was achieved by means of a calibrator and a fine tuning interpolation dial covering 100 kHz. In parallel, the E 311 was sold after the year 1959. The triple conversion superhet with its mechanical-digital display - with the interpolation oscillator „frequency magnifier“, a 100 Hz dial accuracy could be achieved. The receiver was fully capable of SSB reception and had only about half the weight of the flagship EK07 produced at the same time by the competitor Rohde & Schwarz.
Later receivers were sold in a joined operation with Rohde & Schwarz, such as the E401 / 403 with the digital frequency display using Nixie tubes; the maritime radio receiver E410 in solid state technology was available with BCD switch - frequency setting and with mechanical digital frequency display.