I was at one of our local music stores and one of the kids that worked there showed me a trumpet she was considering buying. It was an early 70's Getzen 300. The lacquer was shot and some of the valve caps and slides were stuck. I told her she could fix it up pretty easily... long story short .. I would up doing it for a music book. I noticed it had a brass plug in the receiver. The plug could be taken out and a special microphone hooked up in it. This seems like a really bad design to me. Anyone know anything about these and the effect it has on horn the horn performs when it isn't being mic'ed. In case you're wondering , she loved the way the horn looked.