[Amps] reading 8-10kv with a digital multimeter?

[Steve Katz]

> Hi Gary:
> 
> An easy test of the diodes is to use a 9 volt battery and use one of the
> diodes in series with the battery lead.  Measure the resulting voltage on
> the voltage range.  The voltage drop from 9 volts will be the drop of the
> diodes.  
> 
> I would expect that the diode are probably good.  
> 
> //Could well be, but checking for Vf doesn't assure much of anything with
> the particular die types used in microwave oven rectifiers.  They are not
> strings of 1000 PIV diodes wired in series, as most hams would do.
> Normally, they are die stacks (unencapsulated raw dice placed up against
> each other in a stack to form one long overmolded HV diode) and have some
> interesting failure modes.  The most obvious is when they all char to
> carbon and become a short circuit, or nearly so.  Much less obvious is
> when they fail due to corona breakdown around the die stack, and the only
> way to induce that is to apply high reverse voltage and check for Ir
> (leakage) before avalanche, and then to check BV (breakdown voltage) at
> some reverse current which actually creates some energy, like perhaps
> 100uA to 1mA.  If the Ir is ~1uA to 5uA at 6000V, and then 100uA at 6500V,
> you've got a good stack, with a sharp "knee."  I can't think of any other
> way to actually test such an item without expensive gear like a high
> voltage curve tracer.  Luckily, most people wouldn't even bother making
> such a measurement, since the HV rectifiers found in microwave ovens have
> a "brand new" cost of about $2 each, and it's easy to replace them.
> -WB2WIK/6
> 
> 
> Colin  K7FM
> 
> 
> 
> 
> 
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