[Test-Equipment] HP 403B AF voltmeter

[mrharisn at hughes.net]

Hi Ken,

I had one of those meters some time back.  There was another post, 
maybe yours, a couple days ago about this as well.  I don't think your 
zeners are needed.  

As I remember the AC charger/power supply  runs the meter while 
charging the battery through a series resister.   There is a diode or 
two, or maybe its a relay, in the power supply that allows the battery 
to power the meter when the AC is not present.  There are regulators 
that limit the voltage, either AC or battery, applied to the meter 
circuitry.

I think the manuals Theory of Operation coveres these circuits.

Mike