The Electro-Voice BK-1 is a condenser cardioid microphone. It came highly recommended back in the 80s when I got mine. It needs power to work well and has a 4.5 volt battery in its housing. This batteries were really expensive I remember. When it is low on juice the sound quality goes down hill.
Some say it is one of the best condenser mics ever made and with today’s modern mixing consoles you can feed it with phantom power that supposedly makes it sound much better. I haven’t tried that though.
I used the BK-1 (and a lot of batteries) for all my songs until I got my Shure SM58 in 2012.