[Amps] Bk 875 LCR Meter: was Mallory Caps

[James Irving]

Hi Jim...

The BK875 is a wonderful meter, along with a number of others, for LC work.  However, for those of who wont', or can't, justify the cost, may I recommend the DM4070.  Its available on ebay, and other places,  for about $40, and compares within couple of percent of the "lab grade" instruments.  I have 4 LCR meters, and its the one that gets used the most, or lent out upon request.  Simply outstanding meter for the price.

Much can be made about reading small inductors with these meters... below 1uh to tenths or hundredths of a uh.  I don't put much stock into it; the reading will change depending on where the probes are connected on the component leads... they are that sensitive.  The realization that final adjustment with small coils must be made with a squeeze or a push after installation, with extraneous material cut, off comes pretty fast.

Most of the time, my different LCR meters will read closely.  However, there are times they aren't, and then I keep in mind the core material, number of windings, and the meters test frequency.  Strangely enough, sometimes it hard to say what the actual value of a particular winding is after measuring it with a couple of instruments and finding "large" discrepancies.  I've always blamed  "core leakage" and not measuring near the actual operating frequency.   Seems to happen mostly on multi-winding non-ferrite cored materials.... any thoughts on that?

Not many problems measuring either C or R, though I do put caps through a leakage check at their rated voltages.  I can also measure ESR but don't generally employ that technique outside of a switching power supply.

Jamie, K9JFK



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##  I use my B+K 875-B  LCR meter to test hv lytics. The 875-B and other
similar meter's will read as high as 20,000 uf.  It will also read D factor..and
that feature alone will find a bad cap instantly.  The 875B  reads AC resistance and not dc
resistance..and down to .001 ohm.   With this last feature, you can measure the ESR of each cap
as well.  After going through case loads of new caps, they will typ all read the same esr,
within 1 milliohm of each other, at least for a quality brand of hv cap.  

## That 875-B is worth it's weight in gold.  #1 amp tool in the shop.   Being able to read down to
.1uh  and .1 pf  saves a lot of time and effort when either winding coils or measuring coils, or
measuring caps, and stuff like stray C, tube C, effects of AL side walls, partitions, etc. 
The latest B version I have will also allow to zero out the test leads when on the uh mode, or
resistance mode..and ditto  with C  mode. 

##  for testing HV lytics, the caps have  to be discharged 1st of course.   Depending on brand,some
hv caps are way on the high side, and some brands are way on the low side.   I also have the older
B+K  875-A.    They come with a 3 year warranty, industry standard piece of test gear.  They are
cheap at Mouser. 

Later.... Jim   VE7RF

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