This question had come up a few weeks ago. The service manual says not to power up the oven when the 10811 is disassembled for service. I talked to Dave Montgomery, former head technician on the 10811 line from its begining around 1980 until its end a few years ago. He said that it is OK to power up the oven if and only if the heater transistors are on the "oven mass". Otherwise, they just fry. If the thermistors are disconnected into order to move the oven mass to where the transistors can attach to it, then you can power up the oven circuits for a few minutes at a time, but realize that eventually the oven will run away without the thermistors. Another thing you can do is bolt the transistors to a spare 10811 oven mass, or make a heat sink for them.
Dave also mentioned that cold 10811's should be 500 Hz low, and that a few were made that were 500 Hz when warmed up. These were used for stability measurements. A very few of these left the factory to go to partner companies. He felt that the only crystal failure you could have in the field (other than catastrophic failure where the crystal is dead) would be a leak. There is normally a vacuum inside. It is certain that a leak would lower the Q of the crystal. It could possibly affect the frequency, especially if contaminants get inside. Any frequency shift from this would be to the low side. Hope that clears up some of the questions. Rick Karlquist N6RK _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts