I wired up a D-104 to my Flex 6300.
The PTT keys up right away but audio is not accepted for 1.5 seconds both on AM and SSB
On SSB you don't even got ANY RF for 1.5 seconds. ON AM when I key PTT the carrier is immediate. but audio is delayed 1.5 seconds. The FHM-1 mike works normally.
Here's one source for the Heil HC-104 restoration kit at DX engineering. http://www.dxengineering.com/parts/hls-hc51retrokit
This is my D-104 after I refurbished it and put it into use when I still had my 5000.
It has an impedance issue.Keep it attached to legacy gear . Rumors have it that Ten Tec Radios sound good with the D104 The hand held mike . Mine sounds terrible. Also there are better mikes out there than the 781 . (And it is not the price)
You cannot make any mike sound great if it does not reproduce the correct information.
No amount of EQ will do this .No tone switch 1 2 . NADA
And throughout this discussion nary a mention of where the transmit hi / low cut is set. Testing the "Quality" .
I guess the first thing we loose as we get older is our hearing..