Went out today like promised,to check koss amp out,with tesoro vaquero and 2nd day with 5.75"concentric,decided to go to relic area,were i have found a few button's,and bam,thought it was a quarter but it's not!,this is a special cleaning job here,like for an expert!.also found these button like tags with E in middle.The koss amp worked great!.I was under power lines and could hear the electricity flowing through lines with amp on!.I am not attempting cleaning on this thing!.Chucky.I will send pic in a minute.