I am interested in adding the ability to connect a frequency counter to my older tube radios via a BNC connector. The first one I would like to add this capability is my recently restored Hallicrafters S-85. In my research, I found mention of needing to add 'buffer stage' circuit to isolate the frequency counter harmonics from getting back into the receiver. I came across this posting that talks about this as well - http://www.g3ynh.info/digrdout/d_rdout.html. I'm interested in knowing if this is require when using a frequency counter such as my HP5334A, or my FeelTech FY-6600. Thank you for your thoughtful responses.