Author Topic: Are your Capacitors Installed Backwards  (Read 10061 times)

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Offline N2IXK

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Re: Are your Capacitors Installed Backwards
« Reply #25 on: June 08, 2015, 12:12:23 am »
Years ago, I learned that paper (then) capacitors had the "outside foil" marked for safety purposes.  That lead should be connected to the node with lower DC voltage, since the insulation outside the outside foil was minimal.

The issue isn't safety or insulation, it is shielding.

When used in high impedance circuitry (think tube amplifiers), you want the outer foil to be connected to the node with lower impedance to ground. In this way, the outer foil can act as a shield around the inner foil, which is connected to the higher impedance point.  For a typical coupling capacitor between 2 tubes, the outer foil goes to the plate of the first stage, with the inner foil connecting to the grid of the next stage.

Quite surprising to see that those "orange drop" caps aren't always properly marked. Why bother putting the band on at all if it doesn't indicate anything?  :-//
« Last Edit: June 08, 2015, 12:19:07 am by N2IXK »
"My favorite programming language is...SOLDER!"--Robert A. Pease
 

Offline david77

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Re: Are your Capacitors Installed Backwards
« Reply #26 on: June 08, 2015, 10:46:16 am »
His videos are usually rather good, this one is too.

But his solution seems very complicated for something that could be easily achieved using a DPDT switch  |O.

I guess it shows how to solve a particular problem, not KISS though.
 


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