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 Post subject: Capacitor Confusion
PostPosted: Sep Thu 10, 2020 7:47 pm 
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I am trying to re cap A Silvertone 6173.

My question is: I have some electrolytic caps on hand that should work, but I dont see any mention of polarity on the schematic. How can I find out what way the new caps should go in, or should I just get all non polarized caps?

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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Thu 10, 2020 8:04 pm 
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There are a minimum of two universal rules for the B+ system:
---the most positive point is the rectifier cathode
---the most negative point is the center-tap of the HV winding. (This is often tied to chassis ground, but not always---if you have a resistor between ground and the center-tap, the latter is now negative---common way of generating bias voltages.

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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Thu 10, 2020 8:16 pm 
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Just checked your schematic----all 3 electrolytics go negative to ground.

For the B+, the schematic shows 200-volt rated parts....That's too low--I would use at least 350.**

The cathode resistor on the output tube should be at least a 20-volt part. (The nominal cathode voltage looks to be 10 volts)


** A safe rule is to use caps with a rated voltage 1.5 times the steady-state working voltage.

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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Thu 10, 2020 8:43 pm 
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pixellany wrote:
Just checked your schematic----all 3 electrolytics go negative to ground.

For the B+, the schematic shows 200-volt rated parts....That's too low--I would use at least 350.**

The cathode resistor on the output tube should be at least a 20-volt part. (The nominal cathode voltage looks to be 10 volts)


** A safe rule is to use caps with a rated voltage 1.5 times the steady-state working voltage.


I'm not sure of another thing, let me ask another question if I may. Theoretically, if I were to replace all the caps with polarized caps, how would I know which way to orient them?


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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Thu 10, 2020 9:11 pm 
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There are three (polarized) Electrolytics in your set.

The wax and paper Capacitors are non polarized and can be replaced with these yellow Axial Film Capacitors.

Image
http://www.tuberadios.com/capacitors/

Schematic: • http://americanradiohistory.com/hd2/IDX ... e-0064.pdf
http://americanradiohistory.com/hd2/IDX ... e-0065.pdf
http://americanradiohistory.com/hd2/IDX ... e-0007.pdf

Some of the old μF (microfarad) capacitance values are no longer commonly found, so choose the next nearest value, up or down.

The Voltage rating of a capacitor is how much "juice" that it can handle.
this can be increased.


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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Thu 10, 2020 9:23 pm 
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You may enjoy these restoration videos from Paul Carlson - - (scroll down)...
viewtopic.php?p=3206030#p3206030
just don't buy anything that he is selling - - you do not need it!

:) Greg.


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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Thu 10, 2020 9:49 pm 
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Fishtone wrote:

I'm not sure of another thing, let me ask another question if I may. Theoretically, if I were to replace all the caps with polarized caps, how would I know which way to orient them?


Theoretically, what would be the point of doing that? Polarized caps are generally more expensive than non-polarized ones and may not be available in the sizes or voltage ratings that you need... for the most part polarized caps are only available in sizes greater than 1 uF. And there is no advantage to using them instead of NP caps.


Last edited by lorenz200w on Sep Fri 11, 2020 4:51 pm, edited 1 time in total.

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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Thu 10, 2020 9:54 pm 
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The three Electrolytic capacitors C17 C22 and C23 (multi-section-capacitor) are in a cardboard/metal tube/can under the chassis.
Observe their polarity - - (their Negative leads are tied together).

They can be replaced with individual components or you can restuff the can (canister).


Replacing with individual Electrolytic capacitors.
see→ viewtopic.php?p=3189898#p3189898

Removing and restuffing/rebuilding capacitor cans.
see→ https://www.antiqueradios.com/forums/vi ... 7#p3130557


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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Fri 11, 2020 11:48 am 
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Echoing some other comments---what would be the motivation for replacing regular capacitors with "polarized" (which generally means electrolytic)??

The main advantage of an electrolytic is a smaller physical size for a given capacitance. However, some of the other properties might make the electrolytic not the best choice.

Cost: For the higher values (eg 20uF or so), the electrolytics will be MUCH cheaper than a film capacitor. For the smaller values, I don't think cost is a major discriminator.

For more than you wanted to know, use the tools here:
https://www.mouser.com/Passive-Componen ... s/_/N-5g7r

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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Mon 14, 2020 4:43 am 
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There is an excellent presentation by Mr. Carlson's Lab, I believe is the name of his utube channel, on the subject of determining outside foil on the non-electrolytics used throughout a radio. It is so simple that there should be no reason for not doing it. For instance, on a .01 capacitor, you simply pinch the capacitor body between your fingers and clip your oscilloscope to it. Then reverse the scope leads. Whichever one makes the lowest waveform, simply mark the capacitor with a sharpie pen on the side where the negative scope lead was. The scope will probably need to be set on the lowest setting of the vertical amplifier, and the straight-through (non-x10) switch on the scope probe. You will be surprised at how often that the "outside foil" mark in the factory, is actually the wrong one. The video goes on to tell you which way the capacitor should be soldered into the circuit.


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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Mon 14, 2020 8:40 am 
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rcflyboy wrote:
There is an excellent presentation by Mr. Carlson's Lab, I believe is the name of his utube channel, on the subject of determining outside foil on the non-electrolytics used throughout a radio. It is so simple that there should be no reason for not doing it. For instance, on a .01 capacitor, you simply pinch the capacitor body between your fingers and clip your oscilloscope to it. Then reverse the scope leads. Whichever one makes the lowest waveform, simply mark the capacitor with a sharpie pen on the side where the negative scope lead was. The scope will probably need to be set on the lowest setting of the vertical amplifier, and the straight-through (non-x10) switch on the scope probe. You will be surprised at how often that the "outside foil" mark in the factory, is actually the wrong one. The video goes on to tell you which way the capacitor should be soldered into the circuit.



"Mr.Carlson" has made many very informative videos. However, this bit about figuring out the 'polarity' of mylar caps is insane and has caused much confusion in the radio hobby. The reason there is no "outside foil" marking is because there is NEVER any need for it in any consumer product ! I have sold well over 300,000 capacitors and restored many 100's of radios and this issue has never been of any impact. This is why no modern makers mark the "outside foil" ! I could maybe see it in some very sensitive gear of some kind... but nothing we would ever encounter.

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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Mon 14, 2020 2:30 pm 
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+1
To me finding and marking the outside foil is like those ultra-shielded speaker wires that are sold for several hundred of $. You can show on the scope what they do, but your ears cannot pickup the difference.
As said by Oldradioparts, modern techniques of constructions make the caps impervious to secondary electromagnetic radiation.

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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Tue 15, 2020 12:16 pm 
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"secondary electromagnetic radiation"----What is that?

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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Tue 15, 2020 12:41 pm 
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Was trying to find the article where i read it, but don't remember how it was titled.
Secondary radiation are signals that come from wires near the cap that are conducting current. The old caps, if connected the wrong way, would pickup this signal.
at least that is my understanding.

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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Wed 16, 2020 1:25 pm 
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In any circuit, there can be 2 kinds of unwanted signal path: capacitive coupling, and inductive coupling. To be sure, one can look at a wire carrying 3mA rms at 1MHz, and see it as a transmitter

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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Thu 17, 2020 4:29 pm 
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pixellany wrote:
In any circuit, there can be 2 kinds of unwanted signal path: capacitive coupling, and inductive coupling. To be sure, one can look at a wire carrying 3mA rms at 1MHz, and see it as a transmitter

Can you explain that some more perhaps with an example for a newb?

Thanks

Bill


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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Fri 18, 2020 10:52 am 
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poulsbobill wrote:
pixellany wrote:
In any circuit, there can be 2 kinds of unwanted signal path: capacitive coupling, and inductive coupling. To be sure, one can look at a wire carrying 3mA rms at 1MHz, and see it as a transmitter

Can you explain that some more perhaps with an example for a newb?

Thanks

Bill

Place 2 conductors close together, and you have created a small capacitor. You have also created an air-core transformer----put an AC current in one of the conductors and you will get a current in the other one.
The "transmitter": Electromagnetic radiation involves both electrostatic and magnetic fields. When one changes, the other is created. Antennas can be designed to use either type of field.

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 Post subject: Re: Capacitor Confusion
PostPosted: Sep Fri 18, 2020 11:49 am 
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With caps like the now common, yellow 630V ones, it is never unusual to have the ones mainly in the area of the second detector, getting into strife by inducting the stray RF floating around in that section. I have found over the years that the 2nd detector area, when not well shielded, to be a major source of instability. And using disk ceramics in the wrong place can also result in induction issues.

Some things may look well in theory, but its when they are put into service, that the wheels suddenly and catastrophically: Fall off.

Marc


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