With RF projects looming on the horizon, now seemed like a good time to restock the silver-mica capacitor supply:
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:
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:
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):
Most of the caps are 1%, which is kinda-sorta typical for silver-mica. Then you find something unbelievable:
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.