Part of that number is the date code. 3j15 means it was made on October 15th on some year ending in 3. It's up to you to determine whether that's 63, 73 or 83. It's probably not 63. 83 would have a lot more vacuum ports than the 73 one would.
HTH
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.