I really need help with my MARK III...please

[ratpatrol]

I just got my Mark III..everything was fine and up and running well...Yesterday, I keyed the mic in the AM mode and the power was going to the antenna, The "on the air" light was lit and people on the on the channel could hear me "key up", but there is no modulation...When I switch to USB or LSB...I have modulation...Its the radio of my dreams and I finally have one. I called a technician who makes house calls on radio equipment coming Monday. are there any suggestions or advice from this forum.? I greatly appreciate it it so much in advance..........JR

[tubefan]

check the 6bq5 tube, Wiggle it in the socket. I had a MKIV that lost its am audio every so often and turned out the 6bq5 had a dirty connection. Wiggling it would bring it back. Cleaned the tube pins and socket and never had it happen again.