[time-nuts] Powering up 10811 oven when disassembled

[Richard (Rick) Karlquist]

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