What is a DRY Electrolytic?????

[Magnavox300]

Hi, just bought a Magnavox C5 clock radio for my son to rebuild,
and it only has one can electrolytic.
I was about to order 2 new electrolytics to replace this can,
a 100uf, and a 50uf.
Am I reading this old can right?
Is there any difference between dry, and the normal electrolytics I usually buy??

[N2IXK]

Pretty much ALL electrolytics since the 1930s or so are "dry" types.

The term was originally used to differentiate the then-new paper and aluminum foil types from the older "wet" electrolytic caps which used a liquid (borax?) solution as an electrolyte, and were similar in construction to a wet cell battery. Wet electrolytics went out of favor as soon as the dry types were introduced.

[Jeffhs]

Originally Posted by N2IXK

Pretty much ALL electrolytics since the 1930s or so are "dry" types.

The term was originally used to differentiate the then-new paper and aluminum foil types from the older "wet" electrolytic caps which used a liquid (borax?) solution as an electrolyte, and were similar in construction to a wet cell battery. Wet electrolytics went out of favor as soon as the dry types were introduced.

Interesting. I thought all electrolytic caps, even present-day ones, were the wet kind. How can today's electrolytics work without some moisture in them? I bring this up because modern electrolytic capacitors do dry out, just as the older ones did, causing them to change value. Dried-out electrolytics, as we know (or should know), are a major cause of 60-Hz AC hum in radios and televisions (to say nothing of the thimble-size electrolytics in today's flat screens that can bulge at the top--they can cause this type of trouble and worse), and when these caps short, they can destroy the power transformer in the set if the power supply is not properly fused.

[N2IXK]

Yes, "dry" aluminum electrolytics still contain a liquid electrolyte, but it is absorbed into a separator paper layer between the 2 foils. I guess they should really be called "damp" rather than "dry".

"Wet" electrolytics actually contained loose liquid, which you could hear sloshing around inside. You couldn't turn the chassis of old sets upside down, because the liquid would come out of the vents at the top of the capacitor cans.

Further information on both types:

Wet Electrolytics
http://www.faradnet.com/deeley/chapt_03.htm

"Dry" Electrolytics:
http://www.faradnet.com/deeley/chapt_07.htm

[old_tv_nut]

Thanks for the education!

[snelson903]

while we are on the subject of caps. here's a question i have never really been sure of, when you take a cap. wired in a parallel the lets say 22 mfd 450 v with another that is equil in value, it becomes 44 mfd what then is the voltage rating become together is it now 900 v or 225 v or remain 450 v. could it now be used in a circuit requiring a 800 volt 44 mfd cap ,or stay at 450 v making it a 44 mfd 450 cap. or what is the voltage rating become of two caps in a serise 22 mfd + 22mfd = 11 mfd does the total voltage together drop along with mfd value , or increase because there are two in a series . this is why i have never used caps. in this way unless the voltage needs were way below any concern.

[Magnavox300]

Thanks for the clarification!
Also, am I right in getting a 100uf and a 50uf?
Looks like they put the microfarads next to the proper combination, right?

[N2IXK]

Originally Posted by Magnavox300

Thanks for the clarification!
Also, am I right in getting a 100uf and a 50uf?
Looks like they put the microfarads next to the proper combination, right?

Yes, a 100uF and a 50uF should be fine, as that is the largest set of values listed. Most likely, those are the actual ratings of your can.

Your old can was actually a replacement, and was marketed as being able to replace several ratings of caps, as increasing the capacity somewhat is generally not a problem in power supply filters. A 100/50 could safely replace all those combinations shown (and probably a few others). Just make to get new caps with an equal or greater VOLTAGE rating. The voltage rating on yours isn't visible in the photo.

Originally Posted by snelson903

while we are on the subject of caps. here's a question i have never really been sure of, when you take a cap. wired in a parallel the lets say 22 mfd 450 v with another that is equil in value, it becomes 44 mfd what then is the voltage rating become together is it now 900 v or 225 v or remain 450 v. could it now be used in a circuit requiring a 800 volt 44 mfd cap ,or stay at 450 v making it a 44 mfd 450 cap. or what is the voltage rating become of two caps in a serise 22 mfd + 22mfd = 11 mfd does the total voltage together drop along with mfd value , or increase because there are two in a series . this is why i have never used caps. in this way unless the voltage needs were way below any concern.

For capacitors in parallel, the capacitance ADDS, but the voltage rating will remain the same as the lowest rated unit. 2 22uf/450V caps in parallel form a 44uf 450V capacitor.

For capacitors in SERIES, the capacitance DIVIDES, and the voltage rating ADDS. 2 22uf 450V caps in series effectively become an 11uf 900V capacitor. When series capacitors are of different values, the math gets a little trickier, because voltages may not divide equally across the string. Resistors in parallel with each cap are recommended when using them in series to ensure proper voltage division.

[snelson903]

i dont realy like useing that methed but sometimes you have no choice,thats why i used equil caps and equil voltage value , i have removed caps were someone has done this and even the voltage rating were all different, mfd were different values . that had to be hard on the lower voltage cap. in a parallel circuit ,if i am restoring something its better just to remove all that and use just one if all possible. thanks n2ixk for the info

[Magnavox300]

Thanks for all the expert advise!!
I will go ahead and order a 100uf and a 50uf, with a higher voltage than the 150 on the old can.
Just curious, can you double the capacitance value on a electrolytic?
I needed a 5uf, but I bought a 10uf since I couldn't find a 5.

Magnavox300

[N2IXK]

Originally Posted by Magnavox300

Just curious, can you double the capacitance value on a electrolytic?
I needed a 5uf, but I bought a 10uf since I couldn't find a 5.

In most cases, doubling the capacitance will not cause any problems. Possible exceptions:

Filter caps right off the cathode of a rectifier tube. Using a grossly oversize cap here can overtax the rectifier tube due to excessive charging current. Tube manuals usually specify a maximum capacitance value for each tube type and filter arrangement.

Caps used in timing circuits.

Capacitors used in loudspeaker crossover networks.

Electrolytic capacitors in general have pretty lousy tolerance specs. -20%/+100% was typical for tube era caps

Exact tube era values can be a bit hard to find these days. instead of 20, 30, 50 uF, today 22, 33, 47 are the usual nominal values.

[Magnavox300]

Originally Posted by N2IXK

In most cases, doubling the capacitance will not cause any problems. Possible exceptions:

Filter caps right off the cathode of a rectifier tube. Using a grossly oversize cap here can overtax the rectifier tube due to excessive charging current. Tube manuals usually specify a maximum capacitance value for each tube type and filter arrangement.

Caps used in timing circuits.

Capacitors used in loudspeaker crossover networks.

Electrolytic capacitors in general have pretty lousy tolerance specs. -20%/+100% was typical for tube era caps

Exact tube era values can be a bit hard to find these days. instead of 20, 30, 50 uF, today 22, 33, 47 are the usual nominal values.

So I can use a 47 instead of a 50 uf electrolytic? I thought I should stay at least the same, or go higher?
Or is that the 20% rule, if so how do I calculate that, just so I will know in the future.
Thanks...

Magnavox300

[snelson903]

yeah thats what i have always tried to do keep it as close to the orignal value if all possible ,always up i was always told, just to next nember like 22 for a 20 and so on. i suppose with a cap tolerance of 10 / 20 % a 47 mfd would be ok for a 50mfd i also test mine with a digital meter before i use one ,just because its new dont mean anything now days .

[Magnavox300]

Is that 20X50=100 or rather ten?
As long as I am within 10uf of the 50uf I am okay?
And 47 is only three away?

[snelson903]

i was always told yrs ago to stay as close as you can to the orignal value in most applacations , when talking of voltage higher was always better not over board though like a 500 volt cap when all you need is 25 volts circuit . when it comes to mfd its best to stay as close to the orignal value ,like if the orignal is 20 mfd you use 22mfd or 50mfd you could 60mfd but would really not go any higher , it kinda also depends on what the circuit is, in power supply circuit's you have alittle more freedom . like useing 47 mfd in place of 50 mfd is fine also ,if you have a digital cap. tester and measure it most of the time it will be over 47mfd any way it could read anywere between 45-51 mfd depend on the caps tolerance rating 10 / 20 % and it can also change after is been hot or used for awile . before i replace a cap i test the new one pretty good first its mfd ,then leak test , just because its new doesnt make a good one under working conditions . for the heck of it i got some of though's resister's off ebay the ones that are real cheap ,i checked them for expl. a 10 ohm was really 23 ohm everyone was so out of the ball park it was like they put the wrong color band on it. what happens to it after it get's hot i wounder l o l .