We have two Doty solids probes: A 7mm CPMAS probe with only
triboelectric spin rate detection and a 5mm CPMAS with optical spin
rate detection. After our second (of two) spin rate preamps blew, I
was forced to fix them. Just about the only thing that can go wrong
with these things (besides the wall-plug power supply going bad) is the
Texas Instruments TL083 dual op-amp becoming fried. This was indeed
the problem with BOTH of my preamps and with some help from Ron Watkins
here at CRD, identified a Motorola replacement part (as our stockroom
has a Motorola preference). An LM412 is a pin-for-pin replacement for
the TL083 with better performance (s/n). After pluging it in and
trying it, the jitter on the counter readout does indeed appear to be
less noisy (for both tribo and optical modes) and the first unit hasn't
failed since the chip was replaced. Give it a try if your Doty spin
rate detector goes "belly-up".
Tom Early
GE CR&D
early@crd.ge.com