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I've occasionally come across this symbol which appears to be a capacitor with a wire through the middle - but I've never seen it on anything where I could physically get a look at what component it corresponded to, and I've never seen it defined in a list of component symbols. Have a look at the first schematic here and look at the earth rail - you'll see what I mean. It's always puzzled me - can anyone shed any light?

enter image description here

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  • \$\begingroup\$ Another interesting feature is how this earth "rail" fully encloses part of the circuit. \$\endgroup\$ – Agent_L Jan 2 '15 at 15:08
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    \$\begingroup\$ Yes, not just a 'theoretical' schematic, but strong hints about how it's actually built - the way the earth points below the valves are drawn being another example \$\endgroup\$ – peterG Jan 2 '15 at 15:45
  • \$\begingroup\$ Please note that there are 2 types of symbols in your schematic that might match your text description (given this is a site with non-english speakers). Some caps have an ARROW through them and they are variable capaciors (the ones that are attached to the dials on the front of the product). The other symbol is discussed in the answers below... \$\endgroup\$ – Wossname Dec 6 '16 at 11:57
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If I'm looking at the correct symbol, that's a feed through capacitor.

enter image description here

They are common on RF devices where they allow wires to enter a shielded enclosure.

Looking at the picture from the link you gave here they are:

enter image description here

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  • \$\begingroup\$ That picture together with the text from the same site made me laugh: "As you can see, it is really beautiful". I'll just assume they meant the exterior :) \$\endgroup\$ – Lundin Dec 6 '16 at 12:29
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Those are known as "feed-through" capacitors.

They provide a way to get a wire into or out of a shielded enclosure - the capacitor gives some filtering to prevent unwanted signals from travelling along the wire.

You can see them where components/wires pass through the top and bottom sides of the small enclosure in the bottom view of the radio.

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It looks like a feed through capacitor. The chassis is grounded and the wire passes from one side to the other to form a connection.

enter image description here

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I think this is "Adjustable Capacitor" or "Variable capacitor". From the schematic it seem to control things like bandwidth. In addition is is in parallel with other components so I this cannot be a wire through capacitor.

Check bottom of page: http://www.learnabout-electronics.org/ac_theory/capacitors01.php

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    \$\begingroup\$ Doesn't look like one to me even with reference to that page. \$\endgroup\$ – PeterJ Jan 2 '15 at 13:20
  • \$\begingroup\$ No, the thing I was asking about really is a feed-through capacitor, and I've already accepted that answer. But anyway, welcome to SE. . . \$\endgroup\$ – peterG Jan 2 '15 at 13:48
  • \$\begingroup\$ @user3479957 actually the way the question is worded pointed me to the variable capacitor bit as well, before I noticed what the OP was talking about. \$\endgroup\$ – Vaibhav Garg Jan 6 '15 at 10:09
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"RF" means radio freqruency. Example, when you're in your car trying to find a radio station, you rotate the dial to the radio station you would like to listen to. In order to listen to that radio station, you have to turn dial to match the same frequency of the radio station.

With that being said, the capacitors with the line are variable capacitors. The dial on a radio is a variable capacitor. That is why dashed lines from the symbol are pointing to are dials. The capacactance can be changed to obtain a certian frequency.

Look up Variable Capacitors.

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    \$\begingroup\$ Welcome to EE.SE! OP refers to the feed-though capacitors, not te tunable ones ans this has already been answeed almost two years ago. \$\endgroup\$ – winny Dec 6 '16 at 12:29

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