Naive1073,
The G7 is a mixture of the M49/U67/U47 circuits.
The Lundahl transformer that has been specified by Jakob is a 1+1:5 that is used 'in reverse' to transform the output impendance of the EF86 to a usable region for the following mic-pre.
This means the '5' side is the primary winding and one of the '1' sides is the secondary and leaves us with a further '1' winding.
This further winding
can be used for an equalization feedback.
The useage of this winding depends on the capsule you put into your microphone.
If you are going to use a C12 / K49 or an M7 capsule type no equalization is neccessary and you can omit this winding.
If you are using a K67 type of capsule there is a built-in high frequency lift that needs to be tamed. Otherwise you'll get the famous chinese harshness. If you use this winding for feedback be shure that the phase of it must be 'reversed' to work correctly.
This is what Charlie's and MetalD posts both refer to.
Please check the U67 schematic to get the idea.
I've built two G7 variants. Both have an original K67 in it and I therefore had to connect the feedback network.
If you use a trimmer as Jakob suggested you can even fine tune the response to the talent.
Believe it or not: These G7s are in heavy usage here and beat even expensive available mics freightently easy.
Be warned: A G7 is only as good as the components you put in - go for quality here.
The G7 has been one of my favourite mics for years now - Jakob has done a truly outstanding job!!!
You can see my built here:
http://twin-x.com/groupdiy/displayimage.php?album=455&pos=1
Regards,
Chris
Edit:
Can you please change the thread title to something more usable (i.e. G7 transformer feedback). This makes it easier for others to find if they have a similar question. Many thanks.