mike5150

I have a heil talk box hooked up between my Marshall JCM2000 dsl50 and my Marshall 2X12 cab. I have the head set to 8ohms and I am using speaker cable (not guitar cables) to run the setup into the 8ohms slot on the back of the cab. When I play my volume is never over 6. I am using my Peavey Wolfgang with stock pickups, so nothing super hot. Anyways, when I switch on the voice box and begin to mouth the tube I get a piercing squeal, from the tube, not the PA. I have tried playing with the voice box on and just listening to the tube, and it sounds fine. Just when I mouth it does it make that terrible sound. Any ideas? Is my voice box dead? Are my cables dead? Thanks.