Oh, it is common and fairly easy. You simply say, "the temperature here
will never exceed (some number say) 60d C. You then calculate the
parameters for the crystal oven for a fair margin of error (say, 65d C)

The crystal is about the size of two dimes held face to face. The oven is
about the size of four quarters held face to face with a cutout in the
middle to accept the crystal. On one side of the face of the quarters is a
fairly large resistor (1-5 watts) bonded with thermal epoxy to the face of
the outside quarter. On the opposite face is the temperature sensor,
similarly bonded to the quarter (thermistor or diode; I prefer diodes)

A controllable heater heats the resistor. When the temperature of the
quarters exceeds the temperature set of the thermistor/diode, the heater
shuts off. It is a bang-bang servo. There are a THOUSAND refinements that
you all can have.


Is this still commonly done today? What is a crystal oven, how big, and
how
is the temperature regulated?


Jim