The were not design to be recording units,but for amateur\non-critical\radio use. In that role, and coupled correctly, the D-104 is a great communications microphone. Clean, CRISP, highly intelligible audio that makes each syllable perfectly understandable.
Larry King audio... nope.....ESSB audio...nope, but if you want that, spend a ton of money or use AM or FM. SSB was designed ( and works well ) to be an efficient, narrow bandwidth mode. The audio part of it was deemed acceptable ...and still is.
I have a D-104 Silver Eagle and turn the pre-amp to only two and the TS-440S's mic gain to about 4 and it works very well. The mike gets "OOHS and AHHS" from teenage or younger visitors to my shack because it looks "so retro " or so they tell me. I have no complaints on the build quality and many cab and dispatch services used these mics ( D-104's of any flavor ) for years with millions of key and unkey actions. I used to have a pager ( remember them?) and the ladies that would relay messages used a D-104 microphone at the transmitting end.
They always had crisp, CLEAN, and understandable audio.
Used D-104's ususally need to be relubricated, and it does not hurt to resolder all contacts.Adding a electret element to replace a working UNDAMAGED original element is pure folly, and there are those that have done it. Kind of like putting a Ferrari engine in a Corolla and then hoping somehow that it will be a Ferrari.
There is NOTHING wrong with the audio of a D-104 if one remembers what it was designed to do ,AND if it is not overdriven AND is electrically and mechanically working.
Most new hams, however, have no idea of the tonal design plan that was incorporated into this mic and think it should sound like a studio mike. Then again, even experienced hams still believe that somehow, someway, SSB can become and deliver AM or FM quality audio easily. Sorry folks but theres one word preventing that.......BANDWIDTH!!
Microsoft Word - DG2IAQ Modification Sheet Astatic D-104 Silver Eagle.doc - DG2IAQ Modification Sheet ASTATIC D-104 Silver Eagle.pdf