I have a desk microphone without the cable. I need to put on a cable
that is just a center conductor and shield. It will be about 3 to 4
feet long.

This is a crystal mic going into a tube amplifier. As this is high
impedance, is there a special mic cable ,or can I just use some rg58 or
rg 8x cable without degrading the audio. It is only for communications
quality speech.

I know all about RF type cable, but have not ventured into the audio.