Nuvistor tubes were invented by RCA in the 1950s to solve the many shortcomings of conventional tubes. Unlike them, Nuvistor tubes offer very high reliability, low microphony, low noise, consistency from batch to batch, small size, relatively low power consumption and great technical performance. The tube is made entirely out of metal and ceramic. Making nuvistors requires special equipment.
The results of huge life-tests indicate that the lot failure rate per 1.000 hours for the 7586 (type used in MF) is only 0,475% at a confidence level of 95% to 10.000 hours.
One famous application was in the Ampex MR-70, a costly studio tape recorder whose entire electronics section was based on nuvistors. Another limited application of this very small tube was in studio-grade microphones from that era, the AKG/Norelco C12a, which employed the 7586, being a good example.
It was also later found in the famed Neumann U 47 studio microphone. This microphone was highly regarded by artists all over the world, and was used by many top recording artists such as Frank Sinatra, The Beatles, and many more.