capacitor question on 49 rca
 

Ok, so i have been recapping my rca rutland and am concerned.


Two caps clearly are early electrolytics. The sides have metal ovals, and they are marked with a plus sign.

No i'm findind caps like these, that have one stripe and are marked on the stripe grd.

I'm confused as to if this is an electrolytic. http://paintforcars.com/Merchant2/images/cap.jpg


This is an all wax and paper cap, the sides are not metal ovals.

They are not electrolytic. The polarity is marked to indicate the outside of the foil, which no longer matters.

Ignore it.

The outside foil can be used as a shield against interference. Here is a lengthy page on the subject:

http://www.aikenamps.com/OutsideFoil.htm

As previously stated, this isn't anything to really worry about when putting in modern poly caps.

This article has advice about identifying and replacing capacitors, with photos showing the various types:

http://antiqueradio.org/recap.htm

As David noted, you can disregard the "foil end" stripe, and the value (as well as general appearance) tells us that is not an electrolytic.

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Generally, the band goes to ground when one side of the cap is ground, or to the downstream end in coupling circuits.

Charles

I thought the band went to the upstream (source, plate, lower impedance) side
in coupling circuits, at least in theory.

Doug McDonald

That's what I always heard and did, as well....

If it's for shielding, the plate is at higher potential than the grid.

What matters for shielding is not potential, but AC impedance. A plate typically has
effective impedance in the 1000-10000 ohm range, while a grid (class A) is
infinite impedance at least at audio and TV sync frequencies.

Now I suppose if you worry about insulation, not noise pickup, DC potential
would matter.


Doug McDonald

True, the plate is at higher DC potential. But signal wise, the plate presents lower impedance-to-ground than the grid which the cap is coupling to. Ergo, better shielding is obtained with the outside foil connected to the plate.

I may stand corrected on that now that I think back :bash: . Not being an engineer, I will defer to others on the particulars here. I need to be careful about blurting stuff out in a hurry.

Charles

Don't worry. I been there, done that. Suffered a grand mal brain fart recently about Predicta 2V CRT heaters.:screwy::o

While the occasional misstatement might show up every now and then, this forum is more like a graduate-level discussion on stuff like this. I came in thinking I knew a lot, but everyone kicking things around like this has made me a lot less ignorant than I used to be! This couldn't have happened twenty years ago. Ain't it wonderful? :-)