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I was recently given a bag of electronic components by a relative. These components have been bought in the late 1970s or at the latest in the early 1980s.

Among them were ten components that I initially took for 1/4 W resistors (shown in image on the left): they had the same form factor (about 6.3 mm x 2.5 mm, cylindrical with axial leads) and were also marked like resistors (shown in image on the right).

220 pF capacitors in unusual form factor (left). 330 Ω resistors for comparison (right.)

220 pF capacitors in unusual form factor (left). 330 Ω resistors for comparison (right)

The markings were

red - red - brown(sic!) - silver - silver

If this had been a resistor, this would have been a 2.2 Ω resistor (or an oddly specific 2.21 Ω resistor, which would make no sense given the silver stripe).

Measuring the resistance gave an open circuit reading, but when I accidentally measured them as capacitors, they came out as 220 pF. I assume that the brown stripe used to be black, but that this colour has faded over the years.

My questions now are:

  • Was this style of capacitor common in those days? Is it common now? I have never seen this before.
  • What type of capacitor is this most likely?
  • Since they came out as 220 pF but the silver stripe indicates x 0.01 on resistors, it seems like the silver stripe has a different meaning on capacitors, is it x 1 or x 0.001?
  • This component came out of a hobbyist home computer lab in the 1970s/1980s. What do you need a 220 pF cap for in this context where the fastest CPUs had 20 MHz clock cycles?
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    \$\begingroup\$ Uncommon now but used to be pretty normal. "2 2 1" means 22 * 10^1 = 220 whether ohms or pF. \$\endgroup\$
    – user16324
    Commented Jan 3, 2022 at 14:46
  • \$\begingroup\$ On a four-band colour coding yes, but this has five bands, which threw me. But you're right of course. \$\endgroup\$ Commented Jan 3, 2022 at 14:48

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Sounds like an axial-lead ceramic capacitor. 221 (red-red-brown) is the code for 220pF. The other bands are likely tolerance (+/-10%) and tempco (perhaps +/-10% over the temperature range). Eg. this data from a discontinued product.

They were not uncommon in that era, at least in Asia and to some extent Europe. North American parts of similar form factor tended to have alphanumeric markings.

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  • \$\begingroup\$ Ah of course! You see these markings on disc capacitors. Makes sense, thanks! Any idea what they would be used for in a 1970s/1980 home computer hobbyist lab? \$\endgroup\$ Commented Jan 3, 2022 at 13:46
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    \$\begingroup\$ Maybe a timing or low-frequency oscillator circuit. There are almost infinite possible applications, however not so many in modern synchronous digital circuits. Old style asynchronous logic maybe. \$\endgroup\$ Commented Jan 3, 2022 at 14:14
  • \$\begingroup\$ I forgot to add that these were very probably European capacitors, so you are very probably correct. There were some Siemens electrolytic capacitors in the bag as well (220 uF nominal, now sadly down to about 150 uF and probably no longer safe to use after 40-odd years of electrolyte evaporation). Thanks for the information! \$\endgroup\$ Commented Jan 3, 2022 at 14:45

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