F-I-C,maybe I can help a little here,I must be one of the lucky ones because for me the purr was not only one of the first but easiest calls to make on a diaphragm turkey call.The real key to using a diaphragm is making sure you have a good seal around the call at the roof of your mouth that no air is getting around the call.If air does get around your call,it wont work to its capabilties.It will also prevent you from properly making good turkey talk.Make sure your using a call that fits stationary at the roof of your mouth as this will help in solving this problem.I have seen the purr done on a diaphragm in 3 different ways.1.With your lips.2.With the tip of your tongue.3.With your throat,using like a gargling technique.The easiest for me is using the tip of my tongue.I keep pressure on the call with the middle of my tongue like saying the letter K,and I curl the tip of my tongue up to the roof of my mouth just behind my front teeth and blow a steady flow of air,while flittering my tongue.Once again if you have a good seal around your call you wont have to blow very hard to make any turkey sound especially on calls with light or less reeds.Dont over blow your call.If your having to blow hard to get sounds then air is getting around your call.The harder you press on your call with the middle of your tongue the higher the pitch.Maybe one of these 3 ways will work for ya,"hope so".Practice is the key,lots of it at the start.The more your call is in your mouth the more you will feel comfortable with it.Keep that air flow going through the call and tongue and not around it and you will eventually be able to make all turkey talk as GC said, with alot of practice.Hope this helps!