When we added FM to our AM radio station, we used 310E's. One at a site a few miles from the transmitter and one at the studio about 12 miles away. Both drifted when first turned on even new. But after that they were never turned off, so no worries. My Mac tube tuners all drifted as did my SS MR-77 and the famous 78. Only the MR 80 was and is rock solid from turn on to turn off. OH! my 7084 doesn't drift either.