[drh4683]

There are instances in which the 6GJ7 may check fine, but its characteristics changed enough to the point where it won't oscillate on any frequency, or sometimes it will only oscillate on the high or low end of the VHF section. Try subbing the tube out. How is that tuner? Dirty contacts? Also, very very common for the fine tuning gear that turns the slug on the VHF tuner strip develops a crack split down the middle, where it just spins on the shaft. 9 times out of 10 they are cracked making fine tuning impossible. I take it apart, and drop a touch of super glue on the shaft and spin the gear around really quick to distribute the glue before it sets up. It works perfect and the trouble won't come back.