Capacitors: What, Why, How?
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- Опубликовано: 12 сен 2024
- What is a capacitor? Why are capacitors used? How does a capacitor work? How to replace capacitors? What are the different types of capacitors? What are different types of capacitors used for? The symbol for a capacitor is two parallel lines. These represent metal conductors. One where electricity goes in. And one where electricity goes out.
The gap represents the insulating space between the conductors. This can be air, paper, plastic or an electrolyte. Electrical charges form in this space and it’s the key to how capacitors do their magic.
Unlike a resistor, which loses voltage instantly when turned off, a capacitor holds its charge even when power is removed, and then slowly releases it.
When a signal enters a capacitor, it is altered because the capacitor holds on to its charge and releases it at a different rate. This allows capacitors to smooth a pulsing signal, and that’s just what C23 and 24 are for.
As voltage leaves our rectifier tube, it’s pulsing because half of the AC cycle has been removed. If the pulsing voltage is introduced into the radio’s signal, it will be heard as a loud hum.
By smoothing the pulses, C23 and 24 filter the hum, so we hear just the radio signal.
Because power filter capacitors need to hold a large charge, electrolytic capacitors are used.
Electrolytics use a paper insulator impregnated with an electrolyte. The electrolyte allows electrolytics to hold a greater charge in a smaller space than other types of capacitors. The conductors in an electrolytic are two pieces of foil rolled around the insulator. An electrolyte separates into positive and negative molecules when charged, so one conductor becomes negative, and the other becomes positive.
Electrolytic capacitors fail over time because the electrolyte eventually dries out. That’s why most un-repaired antique radios have a horrible hum when powered up.
The original C23 and 24 electrolytics are housed in this cylinder which is actually two capacitors in one. Here’s the old capacitor next to the new ones I replaced it with. Capacitors have gotten both smaller and more reliable over the years, but even these new ones will fail someday.
Here’s one of the new capacitors getting a lead soldered to it. And here are the two newly installed capacitors. Electrolytics are polarized, so it’s important to install them with the correct orientation.
To pass through a capacitor, a signal must have a constantly varying AC or pulsed voltage. If voltage is DC and stays steady, the first conductor will charge, but never discharge to the second.
Passing AC while blocking DC is an important characteristic of capacitors. Capacitors C15, 19 and 20 do just that in their jobs as coupling capacitors. Coupling capacitors join the output of one amplification stage, with the input of another. C20, for example, allows the signal to pass from the 6Q7 tube, to the 25L6, while blocking DC voltage that would harm the circuit.
As is the case with most of the capacitors in our old radio, C20 is a wax/paper tubular type.
Wax/paper caps are almost always in some state of failure in antique radios. Unlike electrolytics which fail when they dry out, wax/paper caps fail because they absorb moisture which breaks down the paper dielectric. The waxy coating helps slow this process, but over time the paper breaks down and the conductors short.
Here I’m testing one of the old wax/paper caps. It’s supposed to measure .1 microfarad, but is coming in at a whopping .375. Farads are a unit of measurement for how much charge a capacitor can hold.
And here I’m testing the new replacement capacitor which is measuring correctly at about .1 microfarad.
When I first started restoring antique radios I ordered capacitors as I needed them. After a while I realized it would be easier if I stocked capacitors in my workshop. Now I own bags of them like these. You can also see on the right that I drew diagrams of the capacitors in their correct positions before I removed them. Taking notes and photos helps make sure that new parts are installed correctly.
#radiorepair #radio #electronicsrepair #restoration #capacitor
You are an excellent presenter! A previous vid of yours and this one helped me understand the difference in what a tube rectifier does compared to a coupling cap related to AC and DC. I just bought a 300B tube amp with four V-cap ODAM capacitors so I am beginning to better understand their roles. Super vid👍👍
My goodness. Excellent. These videos will be my reference for my tube amp components!
So glad you’re finding the videos helpful, Bobby. Thanks for the fantastic testimonial. Much appreciated!
Big thumbs up!!👍 Thanks for the high quality content mate!
My pleasure. Thank you.
FC - Excellent job explaining capacitors.
Thanks for being my #1 fan, Rick!
Do the new capacitors change the coloration of the end resulting sound as compared to the old caps?
Capacitors can affect sound, yes. As a capacitor deteriorates and its capacitance and leakage values change this can cause issues that can affect not only the sound, but the safely and reliability of a radio. Replacing a deteriorated capacitor with one that is of the correct value and type as was originally specified will return a radio to its original sound, if all else is functioning properly. Capacitors that are of the same type, and have the same capacitance and leakage values will sound the same. Why wouldn’t they?
@@FluxCondenser They might not sound the same for the same reasons tubes, transformers, and other components are chosen for individual performance in guitar amps
No. If they test the same for capacitance, ESR, parallel leakage, tangent of loss, etc. they will sound the same.
I have a Princeton 112 plus guitar amplifier.
It sounds good; but, the bright is harsh, consistent, and lacks the sag, bloom, chime, and moods I have experienced in larger, more primitive style capacitors; which included the blue (styrene?), and wax paper style capacitors.
I want to see if I can squeeze some beefier components into that tiny printed circuit; and, am wondering if some carbon composition, or more primitive type resistors will help to buffer the overall musicality of this amplifier. Consistent, is not always more pleasant "vocally" translating to a good speaker In a circuit: in many cases it seems that heat, and input, create different surprises in those older circuits that are dynamically pleasing, and interactive to the guitars output..
I would like to see a hardwired, large component, including but not limited to; the transistors; and an all rudiment based solid state amplifier; free of tiny integrated circuits, that would prove clearly that vaccum tubes are not necessary to create irregular personality in a reliable guitar amplifier.
Noticed you didn't try to find the outside foil when you replace the capacitors, does it make much of a difference?
On this project I did replace the caps with the foil side oriented correctly. It’s been so long that I can’t remember if I mentioned this in the series or not. If not, my apologies, as I do consider it to be important. I haven’t actually done any testing to see what difference it makes, but I imagine it would be noticeable. These old radios are so prone to picking up noise that every bit helps. Additionally, if the original manufacturers thought it was important there’s no need to second guess. Thanks for the question.
Hi would you mind sharing where you buy your pre war caps from have been having trouble finding them .
No problem, Tadd. Check out JustRadios.com They have pre and post WWII value caps.
@@FluxCondenser Thanks will do
Hi I have a Croydon radio I am replacing the capacitors in it is a chassis model 136 I havnt been able to find much information on this radio one of the capacitors is made by solar part no. D-.1mfd-200 it has two leads on one end with one painted red and one lead on the other end any idea what you replace this with ?
Tadd, are there any other markings on the capacitor? Do you have a schematic? Without seeing it, I’m guessing it’s a multi section electrolytic. One lead is the common and the other two connect to the positive of the two enclosed capacitors. Based on the markings, it’s a .1 microfarad cap rated at 200 volts. That’s a smaller capacitance value than I’d expect to see for an electrolytic, but it’s possible. Either way, with three leads it’s got to a multi section cap of some type. There’s a small possibility, though, that the third lead is just a ground connected to a shield in the capacitor. I have run across those. If I could see a picture or schematic I’d be able to help more.
@@FluxCondenser No , I don't have a schematic I wish I did I don't really think it is an electrolytic it has two metal can ones on top this isn't tied into them just says it's a sealdtite paper capacitor. I have a set of the John F Rider trouble shooter books but can't find this one metal tag on chassis states it is made by the D.R. company Detroit Mi. I googled it and read it was made by Air King but found nothing like it. Has five tubes and would guess mid to late thirties I have never had one yet that has had more than two eletrolytics have never seen one that has three leads but I am not very skilled at this yet either just getting started my retirement hobby.
Tadd, where are the three leads connected in the circuit? Given the .1 MF rating, I’m inclined to believe this is a standard paper/wax capacitor (is that what it looks like?) and the third lead is simply a shield and that lead connected to ground in the radio. If that’s the case, it can be replaced with a standard new, two-lead capacitor and you can disregard the ground/shield lead. Keep the leads on the replacement cap as short as possible and orient the cap as close to the metal chassis as possible to aid shielding.
@@FluxCondenser The one lead marked red is going to groung the one next to it is going to the 6D6 tube socket and the one on the other end ties into a block with three other wires that I believe goes to an antenna coil. I wish I could find someone out here in Arizona that give me a little traing in this but so far that hasn't happened . I joined an antique radio club but that hasn't been much help yet.
OK, sounds like a coupling cap. Just use a .1 Mylar or equivalent rated for 200 volts or more. Install between the tube and coil. Disregard the red lead going to ground. Either disconnect it or cap that wire so it can’t short anything. Again, the third lead is likely just a means to shield the capacitor from picking up stray RF. Caps like this were rare, but they existed. Noise is less likely to be an issue with a modern replacement. Once you have it up and running, you can experiment with shielding the replacement capacitor, though, by wrapping it with foil and soldering the ground lead to the foil. This will be tricky, though, and you’ll have to make sure the foil doesn’t short anything. I doubt that step will be necessary, but you can experiment to see if it cuts down the noise level. Running an insulated wire to ground and wrapping it around the cap will likely have a similar shielding effect, so that’s an option as well. As I said above, if you can keep the leads short on the replacement cap and orient it close to the metal chassis it will be more protected from RF. Most antique radios don’t use shielded caps, so don’t worry about not using one here.
Amazing video