Dude, those are rare. Even the old style chrome face radios are coming stock with an electret "noise cancelling" element, and the switch is dirty or faulty out of the box. Get the "Dynamic" labeled mic in the cb stuff isle at the truck stop, and make sure the plug is compatible, and really have a talker. The "noise cancelling" mic does work as intended, but getting voltage through the circuitry is just dirty engineering, but lets you safely plug in a "Dynamic" mic. Unless there is a battery, or the radio is designed for a lead sending dc volts to the electret module, (which are the radios that can be deeply damaged when a "Dynamic" mic is plugged in) it is really temporary crud.
I assembled a dual element electret this weekend, one element with .25 opening and one with the 1/16 pinhole and it sounds great. They are wired in parallel.
