Events

Illinois Cap Test

From: Mike Schway (msaudio@nas.com)
Subject: Illinois vs Sprague
Newsgroups: alt.guitar.amps
Date: Fri, 27 Oct 2006 16:14:27 PDT

I did some testing today. Sorry, not ear testing, just some carefully obtained numbers:

Materials:

From my own stock, less than a year old: 6 each Illinois 100uF/350V, Sprague 100uF/350V, Illinois 22uF/500V (sorry, only had 4 of these in stock), and Sprague 20uF/500V. As far as I know, they came from only one mfr lot each. Who knows what would happen if I took samples from different manufacturing batches.

Method:

Measured value, ESR and Leakage (at rated V) using a Sencore LC103. Leakage measurement was obtained 25sec after start of test (nearly all electrolytics will show initially high leakage, which decreases over time).

Results:

(means plus/minus standard deviation for 6 samples)

Value:

Sprague 100/350      107.9 +/- 4.5
Illinois 100/350     100.9 +/- 2.4

Sprague 20/500       23.3 +/- 0.8
Illinois 22/500      23.7 +/- 0.2  (note:  only 4 of these were tested)

ESR (ohms)

Sprague 100/350      0.78 +/- 0.10
Illinois 100/350)    0.33 +/- 0.18

Sprague 20/500       1.25 +/- 0.24
Illinois 22/500      3.23  +/- 0.15

Leakage (uA)

(note: since leakage measurement generally drifts downwards with time of test, I chose an arbitrary time of 25 seconds. All values would've been lower if test was taken over a 1 minute period). All values are "OK" as far as acceptability for use in new equipment.

Sprague 100/350      677 +/- 22
Illinois 100/350     490 +/- 129

Sprague 20/500       242 +/- 61
Illinois 22/500      557 +/- 56

So what does this mean?

Overall, both manufacturers make caps which (at least according to these tests) are suitable for use in newly manufactured equipment. No duds were found. In fact when I measured "dialectric absorption" (a measurement related to the ability of a cap to recharge itself on its own...after discharge and removal of supply), ALL caps measured a healthy scant 4%.

In general, the Illinois caps are made to tighter tolerances. Read and weep! Check the standard deviations for all of the tests: Illinois caps generally had lower S/Ds. Values were closer to their rated values. Still, both mfr's caps are HUGELY more precise than what was available 35 years ago where a tolerance of -50%/+75% was not uncommon. Illinois' average tested at an amazing 1% for the 100uF and 12% for the 22uF, Sprague's was 8% for the 100uF and 16% for the 20uF.

ESR for the 100uF was significantly lower for the Illinois, but Sprague had the edge for the 22 (20) uF cap. In all cases, the values fell within acceptable limits.

These tests are obviously non-musical. I didn't listen to 24 filter caps, just took some reliable and relevant numbers. Also, there's no indication on what will happen after 10 years in service (anybody want to do THAT test?) :-)

But hopefully, this will put to rest the myth that Illinois caps are unsuitable crap. At least according to what I can measure, they're as good if not better than the Spragues (at least at the 100uf/350V value). Admittedly, ESR and leakage were higher for the Illinois than Sprague at 22uF, but they're still within normal limits of acceptability.

That said, I still prefer the Spragues for applications where lead length and strength are important, and Illinois where space is at a premium.

--Mike