National WM-702

The thumb wheel is marked with numbers 1 to 10. In the frequency chart above, the green line is the output with the filter wheel set to position 1, (i.e. no high pass filter). The Red line is position 5 and the blue line is position 10, i.e. with maximum high pass filter engaged.

Matsushita aka National aka Panasonic

Japan is perhaps less well known for ribbon microphones as the USA, UK and Germany, but many excellent Japanese ribbon microphones were made in the post-WW2 era from the late 1940s through to the 1970s. 

The company that is now known as Panasonic was founded by Konosuke Matsushita, who was born on November 27, 1894 in Wasamura, Japan. He founded that Matshishita Electrical Company in 1917, making electrical sockets and bicycle lights. From 1923 onwards Matsushita traded under the brand 'National', and began manufacturing radio equipment in 1931. The Panasonic brand name appeared on some Matsushita products intended for export from 1955. Today most of their products are sold under the Panasonic brand. Several ribbon microphones appeared under the Matsushita and National brands, including the VM1 and WM series. Many of these mics are quirky with unusual aesthetic and technical features.

For our museum, we have grouped all of these together under the 'National' brand, even if they have a Matsushita badge.

https://en.wikipedia.org/wiki/Panasonic

Output impedance: 600 ohms

The National WM-702 has a small ribbon similar in size to an RCA 77D or Beyer microphone. The magnetic field is supplied by two block magnets above and below the ribbon and is guided via two steel plates into tapered pole pieces either side of the ribbon. A blast shield protects the ribbon from abuse.

The WM-702 has a unique mechanism for adjusting the bass response of the microphone. The transformer inside the microphone has a solid EI core, presumably made of ferrite. A thumb-wheel on the side of the microphone activates a cunning mechanism which introduces an air gap between the 'E' and the 'I' parts of the core, which in turn reduces the inductance of the transformer. The change in inductance reduces the bass response of the transformer.