My father-in-law passed away back in 1986. He had a large collection of what appears to be radio and tv tubes, mostly NOS. However, in that collection was a box I found interesting. It was Mullard EL37 laboratory matched pair of tubes. Box did not look that great but when I opened it the tubes were in pristine condition and does not appear they were ever used. They look brand new. I do not know anything about tubes so wondering if anyone has insight as to what I have before I put them up for sale. Thanks.