[Hallicrafters] Self resonant frequencies of various capacitors

[Peter Bertini]

Curiousity got the best of me.

Supposedly the capacitance changes with the applied voltage, and can cause
harmonic distortion when using caps with high K factors.

I did a quick bench test setup, using my HP 654A oscillator and HP 333A
distortion analyzer.

The test jig included a high quality audio step up transformer with .33 uF
mylar DC blocking caps used as needed. A 120 volt, well-regulated DC source
was used for a bias voltage across the test cap, feed through a 6.8K
resistor to approximate a low impedance source. A 2.2 meg resistor was used
on the other side of the test cap for DC return and hi-Z termination. Audio
level was 60 volts P-P riding on the 120 volt DC bias voltage.

The noise and/or harmonic baseline, with no cap (direct wire connection) or
DC voltage was down 54dB. With a .01 mylar the noise level stayed at -54dBm.
Subbing a new 0.01 uF cap purchased in the past six months showed no
measurable change in harmonic distortion. All noise and harmonics still down
-54dB relative to the 1kHz signal. It might be beneficial for someone else
to verify these results, my test procedures may be flawed.

Sharply rapping the cap, using an insulated plastic screwdriver handle,
produced noise spikes that were at best around 3mV PP max.

Pete
On Sun, Jan 2, 2011 at 6:53 PM, Carl <km1h at jeremy.mv.com> wrote:

> Here is a short list of a few new caps I tested as I was suspicious of a
> previous posters results.
>
> Equipment used: Measurements Model 59 GDO, HRO-500, R-7000. The GDO dip was
> at the most distance to get a solid dip which is more than close enough for
> his test.
>
> Lead lengths ranged .5 to 1" depending on physical cap dimensions.
>
> .001 1000V disc 120 MHz
> .001 1000V CDE film 25.2 MHz
>
> .01 500V disc 31.8 MHz
> .01 630V Illinois film 11.35 MHz
> .01 600V Orange Drop 9.1 MHz
>
> .02 600V disc 10.1 MHz
> .022 400V Illinois film 8.25 MHz
>
> .03 600V Orange Drop 6.25 MHz
>
> .05 100V disc 6.8 MHz
> .05 100V film 5.6 MHz
> .047 600V Orange Drop 3.7 MHz
>
> I'll let others calculate the inductance of each cap.
>
> Somewhere I have a few Black Beauties that show almost no leakage, I'll dip
> those when I can find them. There are also a few hundred paper caps, NOS
> and
> pulls, on hand that I use for restuffing; I'll see how a few dip.
>
> Carl
> KM1H
>
>
>
>
>
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