They are tube production designation codes. LOL, for you newbies... and almost all of you are. The venerable 6DJ8 tube had many replacements, If you don’t know what type of equipment it was used in you can stop reading here. It was a superior voltage amplification tube to coupe with a amperage amplification amplifier. Actually, the year and vintage I cited was the best ever mad according to all reliable sources.
op asking for help yet being condescending... nice...
having said that -- this is a case where being able to post a pic would be so helpful