For my own edification I am reverse engineering a P65A Op-Amp made by Philbrick Research in 1962. I know I could probably find the schematics somewhere but I want to learn, including identifying components. The component pictured looks like a diode, is marked with 102K on one side and 12BY and 7843 on the unseen surface. I would assume it's a 102 K resistor but 102K seems way out of proportion to the other components and I've seen capacitors marked with 270K being 27 nF. So is this an axial polypropylene capacitor with a 1nF value or is it a 102k resistor or is it even a diode?

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  • \$\begingroup\$ Why haven't you found the schematics? \$\endgroup\$
    – Andy aka
    Aug 9 at 15:06
  • \$\begingroup\$ @Andyaka I'm not asking for schematics. I'll go find the schematic, if it exists. \$\endgroup\$ Aug 9 at 15:15
  • 3
    \$\begingroup\$ @Andyaka will no longer be aggressive or he will not be able to participate on the site. \$\endgroup\$
    – Null
    Aug 9 at 16:23
  • \$\begingroup\$ @Null I acknowledge your instruction and apologize that my original words came over as aggressive. \$\endgroup\$
    – Andy aka
    Aug 9 at 18:26

1 Answer 1


While there's more than one thing it could be, my first guess would be a 1nF cap, \$\pm 10\%\$. For a more final determination, you can either draw it into the schematic and see if it looks right, or take it out of circuit and test it.

I needed to refer to external memory for the tolerance code; the first page that came up when I searched on "capacitor value markings" was this one.

  • \$\begingroup\$ That's what I was trying to do, learn to draw a schematic without looking at the actual schematic. Due to some feedback I just went ahead and looked at the schematic. It's listed as just "1000" which I deduced to mean picofarads. So yes, this is the correct answer. Thank you for trying to work with me to try and figure it out. I didn't know that K was a tolerance identifier. Good to know! \$\endgroup\$ Aug 9 at 15:27
  • \$\begingroup\$ On a 1962 schematic any unadorned number 1 or over would be in pF (so, your 1000), any decimal number would be in \$\mu\mathrm F\$ (i.e. 0.001 = 1nF). I can't remember how they would have expressed 27\$\mu\$F -- I need to go look at some old schematics. \$\endgroup\$
    – TimWescott
    Aug 9 at 19:32

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