I found a large variety of DALE resisters while I was walking around Radio mall in order to look for vacuum tube . I got several ones.
First I didn't notice but there were many kinds of socket and the expensive one cost 10 times as the cheapest one. I asked the shop staff about the difference. of them. He said , "The sound quality is almost same. People who is particular about parts will buy expensive ones." " How is the cheapest one?" " It is made in Japan and not so bad." "Which is the best one ?" " It is made in USA by military specification." "Are the parts made in Japan better?" " He grinned and "All of them can carry electricity." I finally bought 24 sockets made in Japan. He looked eccentric but honest.
I did not buy tube because I could not find my favorite one. He gave me interesting information. According to his advice, the socket is only required to carry electricity. The tubes with good quality was produced before 970. The worst ones were produced 10 years ago in China or Russia because the quality was not controlled. Recent products are almost close to made in USA products in 70's and the quality is getting better. I was not familiar with tubes but I got useful information from him today and I could take pictures of them freely.