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 Post subject: Capacitors backwards ??????
PostPosted: Nov Thu 30, 2017 6:30 pm 
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I buy the yellow capacitors for .001, .002. 005. etc.....Can you really put these in backwards? I thought it didn't matter. Mr. Carlson says yes??



https://www.youtube.com/watch?v=BnR_DLd1PDI


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 Post subject: Re: Capacitors backwards ??????
PostPosted: Nov Thu 30, 2017 6:36 pm 
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ktewell wrote:
Mr. Carlson says yes??

If I expressed my true opinion of that information source I'd be banned from ARF.

- Leigh

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 Post subject: Re: Capacitors backwards ??????
PostPosted: Nov Thu 30, 2017 7:02 pm 
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I've used more than I care to count and I have NEVER cared about which end goes where.

I do try to have their makings showing though.

Obviously, electrolytic capacitors are a different kettle of fish.

Joseph


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 Post subject: Re: Capacitors backwards ??????
PostPosted: Nov Thu 30, 2017 7:04 pm 
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LOL thats what i thought


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 Post subject: Re: Capacitors backwards ??????
PostPosted: Nov Thu 30, 2017 7:20 pm 
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Unpolarized capacitors have... surprise!!!.... no polarity.

Tubular, rolled-up caps do have an outermost layer of foil, which in days of yore was identified with a black band or similar marking on the "outer layer" lead end. Modern nonpolarized cap manufacturers have mostly abandoned this practice. At one time it was standard assembly procedure among radio manufacturers to solder the marked lead to chassis ground when the caps were used as bypass devices. One "justification" for doing this is that the grounded outer layer of foil served as an electrostatic shield.

Caps used as signal coupling devices, of course, can't have one lead tied to chassis ground, so this (mostly imaginary) benefit from having a grounded electrostatic shield was not available. To address this, some manufacturers (Zenith, Saba) used special three-terminal caps where the third lead was connected to a metal overjacket insulated from either "normal" cap lead. This lead was grounded to chassis and the overjacket provided the electrostatic shield for the cap.

Other manufacturers (in fact, the majority of them) got along just fine by using standard two-lead tubular caps as coupling devices. Even so, they went along with "black band to ground" installation convention for bypass caps. I suspect that the motivation for this had more to do with rationalizing the assembly and inspection process than any observed performance differences.

These days, the notion that the performance of a tube radio is going to be noticeably impacted, for good or ill, by the orientation of a nonpolarized capacitor seems to be pretty much in the obsessive-compulsive-disorder-afflicted category. IMO, of course. OCD tube techies, feel free to disagree!


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 Post subject: Re: Capacitors backwards ??????
PostPosted: Nov Thu 30, 2017 8:52 pm 
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You're welcome to your opinions, as long as you keep in mind that they are just opinions. Electrostatic and electromagnetic coupling between components plays a huge role in equipment design and yes the connection of the outside foil of a capacitor does matter in some cases. You might hear some hum or noise or notice a tendency towards squealing or whistling and think, "well that's just how old radios work." But it's not.

The reason they do not bother marking the outside foil in modern caps is because there's no foil there! It's been replaced by a metalized plastic film so thin it doesn't even block light, let alone signals at RF, IF, or audio frequencies. Mr. Carlson's video shows about a 6-dB improvement in noise immunity where a capacitor with real metal foils might have 50 dB (about 100,000 times) the difference.

In many instances you can use modern caps in old radios and get away with it. Increased noise is usually masked by greater atmospheric noise (QRM) and if no unwanted couplings occur, it won't make any difference. No harm, no foul in other words. But if you recap a radio and it starts acting weird, it's worth considering that those outside foils that are now gone might have been connected the way they were for a reason. If you suspect problems of this sort, a piece of copper foil can be wrapped around the cap and grounded, replacing the shielding of the old cap(s).

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 Post subject: Re: Capacitors backwards ??????
PostPosted: Nov Thu 30, 2017 9:10 pm 
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Electrolytics do have polarity and are marked so.
"Foil caps" may indicate polarity needed, or more a ground side. But it would still work as intended, and as Chris said, with possible noise
Yellow caps with no foil, have no polarity.

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 Post subject: Re: Capacitors backwards ??????
PostPosted: Nov Thu 30, 2017 9:12 pm 
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Chris108 wrote:
You're welcome to your opinions, as long as you keep in mind that they are just opinions. Electrostatic and electromagnetic coupling between components plays a huge role in equipment design and yes the connection of the outside foil of a capacitor does matter in some cases. You might hear some hum or noise or notice a tendency towards squealing or whistling and think, "well that's just how old radios work." But it's not.

The reason they do not bother marking the outside foil in modern caps is because there's no foil there! It's been replaced by a metalized plastic film so thin it doesn't even block light, let alone signals at RF, IF, or audio frequencies. Mr. Carlson's video shows about a 6-dB improvement in noise immunity where a capacitor with real metal foils might have 50 dB (about 100,000 times) the difference.

In many instances you can use modern caps in old radios and get away with it. Increased noise is usually masked by greater atmospheric noise (QRM) and if no unwanted couplings occur, it won't make any difference. No harm, no foul in other words. But if you recap a radio and it starts acting weird, it's worth considering that those outside foils that are now gone might have been connected the way they were for a reason. If you suspect problems of this sort, a piece of copper foil can be wrapped around the cap and grounded, replacing the shielding of the old cap(s).


Chris,
does insulation, spaghetti type, on caps leads provide any noise elimination, or is it just for short protection?

Joe

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 Post subject: Re: Capacitors backwards ??????
PostPosted: Nov Thu 30, 2017 10:39 pm 
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It forms a surface to capture marinara sauce or pesto. Bon apetite!

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 Post subject: Re: Capacitors backwards ??????
PostPosted: Nov Thu 30, 2017 10:52 pm 
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Chris108 wrote:
It forms a surface to capture marinara sauce or pesto.


How much sauce? If we have 100% adhesion, simple


Attachment:
surface-area.jpg
surface-area.jpg [ 26.57 KiB | Viewed 607 times ]


Don't bother with the math - the answer is GOBS. :lol:

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 Post subject: Re: Capacitors backwards ??????
PostPosted: Dec Sat 09, 2017 9:20 pm 
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A couple of thoughts.

Modern caps are smaller than the old caps, so there is less chance of the cap picking up signals/interference.

If the cap has a high enough value to do a proper job of bypassing or coupling, the inside and outside foils should be effectively connected together at all frequencies of interest.

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 Post subject: Re: Capacitors backwards ??????
PostPosted: Dec Sun 10, 2017 12:13 am 
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I am in agreement with Leigh, re what we should call some of these people. There is a lot of dangerous and totally false & misleading information out there & it really is reaching the point where the carriers should be trampling on the civil liberties of hundreds & remove them in the interests of public safety.

I have in the span of over 50 years replaced thousands of caps. My only concern with NP ones, is to put them in so that you can read whats on them (for senior moments) orientate them, (and resistors) where possible, in the same direction to make them easier to read.

With modern caps induction can be a problem, moving them to a new spot can cause that, but not always. Often I have had to replace wire with shielded, & rarely, shield the cap. The 2nd detector area, being the worst offender. Lead dress is always important. wires etc, in mid air, risk being radiators & antennas, leading to instability.

You are better off asking questions here, even that you may get a dozen opinions: None of them will have the intent to mislead.

Marc


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 Post subject: Re: Capacitors backwards ??????
PostPosted: Dec Sun 10, 2017 12:20 am 
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Here's the crux of the issue:
There are people who take the fine points of the theory and present them in a way that implies that--- unless everyone follows all the details---disaster will surely strike.
Chris108 and others correctly point out that the "polarity" can make a difference. The practical reality is most situations, it does not matter.

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 Post subject: Re: Capacitors backwards ??????
PostPosted: Dec Sun 10, 2017 12:32 am 
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pixellany wrote:
Here's the crux of the issue: ...
Chris108 and others correctly point out that the "polarity" can make a difference.
The practical reality is most situations, it does not matter.

It probably did not matter in the original design.
I think folks migrating from earlier sets with marginal B+ filtering were overly sensitive to hum in the audio.

It certainly does not matter with modern caps.

- Leigh

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 Post subject: Re: Capacitors backwards ??????
PostPosted: Dec Sun 10, 2017 12:41 am 
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glue_ru wrote:
Chris,
does insulation, spaghetti type, on caps leads provide any noise elimination, or is it just for short protection?

Joe

If you wad it up and pack it in your ears there may be a 10db sound reduction.

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 Post subject: Re: Capacitors backwards ??????
PostPosted: Dec Sun 10, 2017 1:02 am 
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Capacitors, except for electrolytics do not have polarity, they do not have a plus or minus, they do have markings identifying the outside foil end, lets not refer to this marking as polarity, things are confusing enough for the newcomers.

Dave


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 Post subject: Re: Capacitors backwards ??????
PostPosted: Dec Sun 10, 2017 2:18 am 
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This may come as a surprise to some, but Chris108 really couldn't care less which way you hook your caps up. Of course if the cap is a polarized type (electrolytic, tantalum, or polymer) then you better respect the polarity markings or you'll ruin the cap and maybe damage other components. If the cap is not polarized, then it doesn't matter which way you connect it. This includes modern film caps which don't offer enough screening to be worth bothering with, with all due apologies to u-tube.

The point I was trying to make is that there were and maybe still are some situations where the screening effect of grounding the outside foils of caps was used to prevent unwanted coupling. Certainly not in every radio or amp circuit, and even where it was used, it was only marginal at best. Just be aware that it existed and may have to be replicated in certain cases.

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 Post subject: Re: Capacitors backwards ??????
PostPosted: Dec Sun 10, 2017 7:14 am 
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Greetings to the Forum:

Chris108 writes:

Quote:
Increased noise is usually masked by greater atmospheric noise (QRM)


As long as we are nitpicking, QRM is interference, i.e. other stations on the same or nearby frequencies. QRN is atmospheric noise or "static".

CW practice:

QRN? = Are you troubled by static?

QRN (without the question mark) = I am troubled by static.

QRM same question and answer except substitute "interference" for "static".

I can nitpick with the best of them. :D

Regards,

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 Post subject: Re: Capacitors backwards ??????
PostPosted: Dec Sun 10, 2017 11:06 am 
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easyrider8 wrote:
Capacitors, except for electrolytics do not have polarity, they do not have a plus or minus, they do have markings identifying the outside foil end, lets not refer to this marking as polarity, things are confusing enough for the newcomers.

Dave

Point taken...the other confusing usage of that word comes up with transformers....the dot notation. In school, we learned it is "the polarity of the induced voltage". It would have been better to say something like "phasing".

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 Post subject: Re: Capacitors backwards ??????
PostPosted: Dec Sun 10, 2017 1:17 pm 
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Point of fact, QRM is CW notation for noise or interference, Manmade. QRN is noise or interference, Natural. Over the last 40 years or so both have increased, but the amount of manmade electromagnetic pollution has gone up far, far higher and can be heard nearly anywhere on earth now.

In this context, a radio with haphazardly chosen and installed replacement caps in the RF or IF sections could be noisier or more bothered by interference from other stations, which is why the term was used.

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