Armstrong A221 valve amplifier tube question
I have a vintage Armstrong A221 intergrated amplifier which has a pair of ecl86 tubes,i had the top of last night and noticed one of the tubes has has been damaged,it has a small hole in the top?. I picked it up at a garage sale and it sounds great:). My question is that i have a pair of el84 valves spare formy headphone amp and would like to know if they can be used to replace the el86 tube that is damaged ? The amp sounds fine but this el86 tube will need replacing and i dont know much about valves?? Thanks .