Silver-Mica Capacitor Assortment

With RF projects looming on the horizon, now seemed like a good time to restock the silver-mica capacitor supply:

Silver-mica capacitor - assortment

Silver-mica capacitor – assortment

That’s 150-ish little brown envelopes, found on eBay in the lowest-entropy state I can imagine, with about 11 pounds of caps delivered for a bit under $5/pound.

The envelopes bear date stamps from the mid- to late-60s:

Silver-mica capacitor - 188 pF 0.5 pct - envelope

Silver-mica capacitor – 188 pF 0.5 pct – envelope

I think these came directly from the Electro-Motive Mfg Co production line or QC lab, because some of the envelopes have notes about “WE”, “Bell Labs”, and suchlike. They seem to be special-production items, not the usual caps from your usual distributor.

The values and tolerances are weird beyond belief:

Silver-mica capacitor - 6160 pF 0.5 pct - on envelope

Silver-mica capacitor – 6160 pF 0.5 pct – on envelope

If you’re taking notes, 6160 pF lies halfway between the 6120 and 6190 values in the E192 series.

And, yes, that’s a cap with ½% tolerance (forgive the bright-red color imbalance):

Silver-mica capacitor - 6160 pF 0.5 pct - detail

Silver-mica capacitor – 6160 pF 0.5 pct – detail

Most of the caps are 1%, which is kinda-sorta typical for silver-mica. Then you find something unbelievable:

Silver-mica capacitor - 22.8 pF 0.1 pct

Silver-mica capacitor – 22.8 pF 0.1 pct

Stipulated, I’ve lived a sheltered existence. Have you ever seen a 0.1% tolerance cap? The assortment has more of those, scattered throughout the range.

Regrettably, the entire decade from just over 300 pF to just under 3000 pF has gone missing: somewhere out there, someone has another box from the room that housed this collection. So it goes; given the plethora of values, I can always make series-parallel combinations to get what’s needed.

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  1. #1 by Keith Ward on 2016-11-10 - 07:40

    Eleven pounds of caps? You should be set for a while, if not life, or at least for your current RF projects.

    Regrettably, the entire decade from just over 300 pF to just under 3000 pF has gone missing

    Maybe that was the one series that actually passed the grueling tests and went on to Western Electric / Bell Labs?

    The transition of W.E. to Bell Labs to Lucent Tech, and now finally(?) to Nokia has taken quite an arc over the years. My work with them ended several years ago now. After surviving for over 12 years of layoffs, my number finally came up. The days of being designed to last for 50 years are now long over for them. Maybe only the folks at NASA work to those type of standards now.

    series-parallel combinations to get what’s needed.

    Reminds me of the ever amazing 3D wiring structures created by so many HAMS. Always seemed like everything should be potted after finally getting the circuit to finally work!

    • #2 by Ed on 2016-11-10 - 08:19

      That block seems surgically removed. I don’t know why anybody would leave the two ends of the collection, so it probably came from two people loading two boxes at once. Dang!

      (I un-nested the block comment things in your note.)

  2. #3 by madbodger on 2016-11-10 - 11:51

    That is quite a haul. I’m tempted to go through my stash, find some in your missing range, and offer a trade.

    • #4 by Ed on 2016-11-10 - 13:18

      The envelopes hold anywhere from zero (I tossed that one) to 30-ish caps, with most in the 5-to-10 range. The prospect of maintaining the low entropy by re-bagging / labeling half the loot seems daunting; I briefly considered buying half a dozen more parts cabinets (*), then came to my senses and sorted the envelopes into three rows in a cardboard box.

      I’d have to feel ’em all up to know how much I could split off for you …

      (*) Dunno if I could bring myself to combine the 90.9 pF and 91 pF caps into the same bin. [grin]

      • #5 by Keith Ward on 2016-11-10 - 14:42

        “(*) Dunno if I could bring myself to combine the 90.9 pF and 91 pF caps into the same bin. [grin]”

        That might keep me up at night just knowing you are considering it ;-)

        • #6 by Ed on 2016-11-10 - 15:33

          The weirdest part: they’re both ±1% = ±0.9 pF, so they’re exactly the same.

          I wonder about the envelopes of 297.9 and 298 pF caps, too. They must have had some reason for separating those ±1% lots; we’ll never know the rest of the story.

  3. #7 by Raj on 2016-11-12 - 03:35

    Ed, I see you have the AADE meter. Have you noticed that plastic case is crudely cut to accommodate the push buttons? I dismantled mine, put a flat faced steel burr on the stand drill and neatly milled the cases to make the slot neat. You could do that with your other machines.

    • #8 by Ed on 2016-11-12 - 08:32

      The tidy slot in this case suggests either CNC milling or a low-caffeine morning: the buttons work perfectly!

      The guy died last year, so there will be no more AADE meters.