I’m an audiophile and my father is a Grammy award winning master engineer. Here’s what I’ll tell you, the V6’s which are the 7506’s sister, halted production in the early 90s due to a wire issue. The 7506’s were conceived by Hidako Iwasaki in 1974 and produced in Japan in early 1975 with a total production run of 31. Then in May of 1976 they were released in the US with a total production run of 76, hence the year. The were produced sparingly through the years and only given to prominent DJ’s and talk show hosts until the early 90’s..January 4 1991 to be exact when Sony decided, because off all the feedback, to go into full production and the US was shipped 1,500 units. Sears, Douglas, Highland were a few of the stores that carried them during this time frame. The response was amazing. Then in the summer of that same year, Sony produced over 25,000 units and the MDR 7506s outsold Koss in its first year. The V6’s are also Sony’s second best selling headphones up until 1999.
Just because the correct info isn’t on the internet, it doesn’t mean it isn’t true.