[time-nuts] HP-428B What I really meant....

[Michael Baker]

Hello, TimeNutters--

Oops!!  I goofed--

I meant to say HP/Agilent 428B Sensitive Clip-On DC Milliammeter.

Only the latest revision model with a serial number
prefix of 995-xxxxx is worth having. 

In their last revision, HP retained a couple of tubes in functions
where they felt early 80's transistors would be less reliable.
However, most of the circuitry is solid state and is all on a
very nice printed circuit board.  The unit went out of production
in 1984.  The probes are extremely fragile and if dropped
or exposed to excessive heat for long periods of time
the ferrite cores or the Mu metal shields will be degraded.

The manual warns against storing the probe on top of
any hot instrument top.  My 428B has been an invaluable
and frequently used test instrument on my work bench.
Alignment was a little tricky but once done, my unit
has been in use for over 10 years with no problems. 
It is very handy for measuring low current drains of
circuits down around the 1 to 10 milliamp range. Actually,
on the lowest scale (0 to 1mA) you can accurately measure
currents down to 0.1mA. 

Mike Baker
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