[Elecraft] CAPACITOR VALUES

[Tom Hammond]

Hi John:

>Encouraged by the book to do so, I checked all the capacitor values.   I 
>had just purchased an autoranging DMM with a capacitance measuring feature 
>(the first time I have ever owned such a device) and began to go through 
>the packets. All the monolithic caps checked out fine, so did the 
>electrolytics but, when I turned to the NPO caps, I began to get very 
>strange readings from most of them.
>
>For example:
>
>   1pf   read    21 pf
>     10pf    read    35PF
>     12pf    read    38pf
>     20pf    read    51pf
>     27pf    read    62pf
>     33pf    read    70pf
>     39pf    read    77pf
>     47pf    read    90pf
>
>     and so on up the scale ad nauseum.
>
>My first inclination was to think that either my DMM was faulty (this was 
>its first job, after all) or that Elecraft had tracked down a supply of 
>dud parts (unthinkable). However, a little reflection reveals that all the 
>capacitors of a any given value gave the same meter reading and that, as 
>the marked values increased, so did the indicated values, albeit by a 
>factor of around 2:1. All of which leads me to suspect either the DMM or 
>the way I am using it.

The fact that ALL of these caps are of small value, and that all are high, 
by 20-45pF, tends to imply that your cap. meter is showing you a moderate 
to significant amount of 'residual' capacitance, probably due to hand or 
lead capacitance, and NOT due to the actual capacitor being off-value.

When you're reading the larger value caps, you wouldn't notice this 
residual capacitance because (although it's still there) it's being 
'swamped' out by the much larger capacitance value. Who would notice an 
added 20-45pF on a cap which already measures 1000pF?

You're good to go, John.

Stop worrying and start slinging solder. And HAVE FUN.

Cheers,

Tom Hammond    N0SS