I just retubed a friends Blues Deville after he blew a fuse. The amp had original tubes in it an I figured that one of the 6l6s had just given up the ghost. I retubed it with some gt black plates and after about a month one shorted. I thought that the issue was amp and have gone through it and can't see anything obvious. I have dropped in a set of pulls and the amp is running fine...... anything else I shoudl check, voltages are all good.