[Milsurplus] Electrolytics

[Nick England]

For many many years resistors and most capacitors have followed the RETMA
standard values
10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 or
10, 15, 22, 33, 47, 68

But electrolytics didn’t, for some reason. Until we started seeing
tantalums and the Japanese electrolytic invasion. I wonder why? Maybe
because of the lopsided -20/+80% tolerance?
But we commonly saw 20 and 40 uF values when they could have been 22 and 47
just as easily. Mysteries.

Nick England K4NYW
www.navy-radio.com


On Wed, Aug 20, 2025 at 11:15 AM Charlie L. <mjcal79 at gmail.com> wrote:

> Thanks Jim and David for the comments.  One thing about electrolytics is
> that our old units seem to have a tolerance rating of -20/+80% of indicated
> value. Most folks want to replace, say a 40uf at 450VDC, with the same
> thing, and end up paying $10 or more for a name brand, while you can find
> the 39uf at 450V and higher for just a few dollars.  A lot of the smaller
> caps are also abundant  with a 630VDC rating at an inexpensive cost,
> compared to being a purist and wanting .1 at 600 for $5 where the .1 at 630V
> can be in the 50 cent range.  When you use Newark or Mouser, a big giveaway
> when you are putting in the part value in the filter window and you see
> three 40uf listed and 72 39uf listed, you know the 39's will be cheaper
> with a greater voltage range selection.  The 20uf cap was ubiquitous in
> just about any gear years ago, Newark has 3 choices for a 20uf and 28 for
> an18uf, well within the acceptable  tolerance.  I thought when Newark
> started selling leaded resistors for a fraction of a cent each, that they
> were dumping stock,  as everything seemed to be going to SMD style, but
> maybe that is not the case.
>
> Charlie in NC
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