We have a VSS mass spectrometer model MS10, connected to a control unit
type RGA10. The output of the unit is affected by a slow random fluctuation
of more than 1 V in amplitude which makes the system unusable.  After many
tests and trials we concluded that the most likely faulty component is the
double-JFET in the electrometer head.  Unfortunately that component, an
Analog Devices AD830, is now obsolete.

1. Has anyone had similar problems or does anyone have suggestions on the
matter?

2. Does anyone know of a source for the AD830 or of an equivalent device?

3. Would anyone in Australia with a MS10 not currently in use be willing to
loan the head+control unit for a few days to allow us to isolate the cause
of the fluctuations?

If you wish you can reply to me personally to this address:

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Thank you very much in advance.


Dr Giuseppe B. Scelsi

--
Optical Fibre Sensors group
Division of Physics and Electronics Engineering
University of New England
Armidale  NSW 2351                      Tel.:  + 61 - 2 - 6773 2426
Australia                               FAX :  + 61 - 2 - 6773 3413