I thought of this - I swapped out a rectifier tube recently in my 67 Vibrolux and, within a month, I blew an NOS RCA blackplate 6L6-GC. Weird. I wonder if that's related? There was a chinese tube in it and I swapped in an NOS Sylvania without thinking about it... Now my tubes don't bias worth a crap - I'm getting 34/35ma on my power tubes with the bias pot cranked up. Does the rectifier tube (quality of, brand, etc) have anything to do with biasing/current to power tubes?