W0VMC Robert sells an inexpensive kit for the modulator deck. It comes with a schematic and all the parts to install on the preamp tubes. Its actualy easier to order his kit that it is to sit down and figure the values and order all the caps and parts.
He also sent me the correct Screen and filiment bypass caps for the final tube. You need to change these for full bandwidth audio.
Once this was done, I use the phone patch jack on the rear of the mod deck for the mic input. I use a Low to high level impedance matching transformer (from guitar center). This converts to low impedance to my inexpensive 802 mixer and then to my Large diaphram condensor mic.
I swept the 500C after all this was done and I ended up nearly flat from 20hz out to 10,000. With some EQ, I reach 12,000. I was suprised the stock mod iron could go that low but it does. Everyone that has listened to my 500 loves it. Its very wide, full and clear.
Of course,, I can still run the D104 if I want. He even supplies the correct loading resistor for the D104 so you get pretty decent sound from the old mic.
HIs website is
http://www.w0vmc.com/He is on this site as a user also. Also.. search for my Globe king 500 under my user name. I posted a full instruction manual on the restoration of my 500 that might help.
Clark
