The instrument
The D 19 launched in 1953 is the first with 200 ohms. Many variants were made, reflected in the letters after the model number. The D19C used a three‑pin locking DIN connector. The D19E used an XLR with a five‑pin connector, who presented all three options 60Ω, 200Ω and 50kΩ ‘Hi’.. There was also a D19B; it’s not clear what the B referred to, but some D19Bs were designated BK Hi. The K indicates that they had a captive cable and the Hi that they had a high‑impedance output for connecting to tape recorders. Some D19s with the suffix S had a large on/off switch. (soundonsound)
Details
"The frequency range of the D 19 should extend from 30 ... 16'000 Hz; its smooth frequency response must deviate no more than +- 3.5 db from the flat ideal curve. The distortion at 1000 Hz and 180° angle of incidence of sound should be better than 18 db. A continuous bass attenuator should cover a range from 0 to -10 db at 50Hz and be easily controlled by an adjusting ring located on the neck of the microphone." (Manual AKG D 19)