Hi again Andrew,
You'd have to hunt around the web for details but luckily I won't send you up the 'Google it!' path
It's always best never to assume wiring colours but trace them with a multimeter. However CRT did stick with a standard colour scheme. The colours and function are as follows :-
Shield - Ground
White - Audio (as you say 'modulation' or mic audio)
Red - PTT (Push To Talk)
Blue - NC (Not Connected)
It does become a little more complicated for the Up/Down functions....
A resistor of 3K9 value goes from the PTT connection (Red) to the 'Up' button. (It connects this to ground when the 'Up' button is pushed.)
Another resistor this time of 2K2 value goes from the PTT connection (Red) to the 'Down' button. (Similar to above but the 'Down' button connects this to ground.)
...and Bob's your Uncle
You'll see how these connections work if you look inside your original CRT microphone.
You might need to fiddle about connecting these extra resistors to your wiring or you could even forget about them and just use the audio, PTT and shield ground. (Some mic adapters don't even bother with the up/down functionality!)
Well done for having a go yourself, (always admire someone's DIY efforts), and let us know how you get on.
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All the best,