There is a mod for the D-104s that are amplified that works very well and tends to make them even better sideband performers , I believe even Astatic reccomended the mod which was a cap and a resistor in line with the audio line terminal from the bottom of the mic , I just restored a TUG-8 base ,the guy who is using it now has no problem with back ground on AM and tends to talk close to his mic , I can surely hear the differance with the cap and resistor in line . I was very impressed ,but more so on the ssb side , very clean where other D-104s sounded over driven and splattery , the cap and resistor was surely a plus.