  Commercial quartz oscillators of the tuning-fork type with a resonant
frequency of ~32 kHz have been investigated in helium liquids. The oscillators
are found to have at best Q values in the range 10^5-10^6, when measured in
vacuum below 1.5 K. However, the variability is large and for very low
temperature operation the sensor has to be preselected. We explore their
properties in the regime of linear viscous hydrodynamic response in normal and
superfluid 3He and 4He, by comparing measurements to the hydrodynamic model of
the sensor.
