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Understanding Tuning Capacitors: Antique Radio
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- čas přidán 18. 08. 2024
- This video is designed to give you a better understanding of the tuning capacitors in antique radios, as well as understanding schematic symbols for them.
Thanks great video helps with my understanding. All the best Bill
How the capacitor was a big help to me I had problems too and this solved a lot of my problems and I thank you very much it was a great
Thank you for making this video. Your description is way clearer and easier to understand than many other way I have heard the air capacitor explained.
Thanks John! That was really straightforward and simple to understand.
Thanks, I don't remember learning about tuning capacitors, how they are connected and why, but you did an amazing job making it understandable
Nicely done Mr. Richter. I’ve been playing with radio for over 50 years. I’ve been an engineer for over 30 years. Your description of a variable capacitor and explanation of its function is concise, accurate and easy to understand. Well done! Keep up the good work. Howie WA3MCK.
What a nice compliment Howie. I'm flattered. Thank you.
Thanks mate..my radio interest started in 1957 and continues. My favorite component was always the tuning condenser. 24NOV2017
As always, very helpful, John. Since I can't have someone by my side, videos like this are the next best thing. Cheers!
Good information! Many of us hams/radio enthusiasts have beat our heads in the wall deciphering some parts of old schematics. It's also amazing how we went from say cycles (kc, mc etc..) to using Hz...many old schematics will use those mc or kc to represent Mhz or Khz. Good job, someone has to keep history of how it worked alive or those old radios will be dead.
Thank you very much for the information! You have helped me so I can continue helping the planet. So thank you for your contribution of knowledge and the time you took to make the video. Its the small things like this that can really make a difference.
Thank you for making and posting this tutorial video. It was very much needed by myself, and no doubt, many others!
This video will make a huge difference in the success of my projects. Thanks,
Per your request, you need to make a correction to your explanation of the Red and Blue capacitors. The capacitors with the dashed line between them are the main tuning. One for the RF signal from the antenna, the other for the oscillator circuit. The Red capacitors in the drawing are the trimmers.
A point about the tuning capacitors in vintage equipment. As John mentioned, the rotor is electrically - and mechanically - connected to the frame. BUT the rotor's electrical signal must pass through bearings (sometimes bushings) in the rotor mount. These bearings can often corrode and/or disintegrate, causing intermittent or completely failed electrical connection. And it is equally important to note that almost all off the shelf lubricants are insulators, and if applied to the bearings during maintenance will insulate the rotor from the frame!
IF you need to lubricate, you need to use an ELECTRICALLY CONDUCTIVE grease. Silver bearing. It is expensive :)
Excellent point. Conductive grease is definitely the answer for bearings or bushings that are oxidizing, especially if the current path includes those bearings or bushings.
GREAT STRONG VOICE AND VIDEO PRESENTATION AS WELL . THANK YOU SIR .
Greetings:
The tuning capacitor has one section that forms half of a "resonant tank circuit" that requires an inductor that together with the tuning condenser resonates at frequencies that cover the broadcast (medium-wave) band from about 550 kilo-Hertz to about 1700 kilo-Hertz (aka 1.7 MHz). In the absence of a loop or loopstick antenna a longwire external antenna is used to collect radio broadcast carrier waves that are used with the local oscillator tank circuit to create the Intermediate Frequency (IF) in the convertor tube, also known as the mixer tube. That local oscillator tank circuit is formed by a separate inductor paired with the other portion of the ganged tuning condenser.
BTW: The local oscillator portion of the tuning condenser can be of the same capacitance range as the other half or it can be lesser in capacitance while it is paired with an appropriate inductor such that the local oscillator frequency range produces a difference frequency that tracks with the frequency range of the antenna portion of the tuning condenser tank circuit in a way that always results in a difference frequency that becomes the IF frequency in the convertor tube's output. Typically the maximum capacitance of the antenna section is historically about 365 pico-farads.
In the schematic shown, the loop antenna is the inductor that forms the tank circuit with the larger section of the tuning condenser. That tank circuit is tuned so that the impedance top to bottom is greatest when the frequency matches that of a broadcast station's carrier frequency. That high impedance keeps the desired carrier from draining off to ground and instead goes into grid 3 of that tube. In addition to the antenna signal, the antenna loop will later be the path for the DC AUTOMATIC LEVEL CONTROL to reach that same grid to reduce the gain of strong station signals (strong signals produce a more negative DC level that has the affect of reducing the gain of that portion of tne convertor tube as well as that of the IF tube - Hazeltine patent). The local oscillator connects to grid 1 where it gets amplified for the mixing process.
The RED capacitor adjacent to the capacitor used for antenna tuning is the trimmer capacitor affixed next to the lug of the stator. The trimmer capacitor is formed by a sandwich of two plates separated by a mica dielectric. As the screw on the trimmer is turned clockwise the capacitance increases as the two plates of the trimmer are forced together. That capacitance is added to that of the larger movable section indicated by the trimmer being drawn in parallel to the
larger section.
What determines the pico farad range of a variable capacitor, is it the size of the rotor/stator fins or some other component of the capacitor? As noted below this is the clearest explanation available of what a variable capacitor is and what it does.
Thank you
Nice work. Exactly what I wanted to know. Thanks.
Andrew Olivera Excellent, thanks. KD4KEN
Good information, thanks for sharing John!
Hey John- Love the video and your explanations. When is part 2
Nicely done. Thank you.
Nice video. But at 6:43, I'd expect the dotted line to connect the air capacitors, rather than the mica ones, given that the air caps are linked together. Seems that for a while, the better-made receivers still had variable air capacitors for tuning, while the cheaper ones had those mini tuning caps with plastic (mylar?) liners. I've always wondered if the air capacitors had better performance, or if they were just part of the a design that hadn't been updated. The plastic lined ones were probably more reliable, on the average.
Thanks.
I always thought that the ganged air capacitor (M1) was the ones joined with the dotted lines while the mica (trimmer) capacitors were the ones in red.
TNikoli you are correct. On electronics schematics the dotted line between variable capacitors, resistors and switches indicates they are ganged (directly connected) and therefore one common shaft controls many parts simultaneously.
John Richter is correct in saying the curved portion of the diagram indicates the variable part in both parts of the diagram, the tiny arrow on the curve for the mica trimmer capacitor, and the rotor in the air variable portion.
But I applaud John for taking the great effort to repair an old radio and learn something in the process, and to record and pass on his knowledge! Those things are cantankerous by nature.
Your video helped me very much. I see why now I'm getting weak signals. ? Should I use one variable capacitor that's much larger and a small 365 variable for fine tuning or do you have a better suggestions? Thanks, I hope you keep producing more info.🤔
Most old AM receivers use a variable capacitor in the low picoFarad range. I can't remember what range exactly but it should be easy to locate on the web. If you have a capacitance tester you can check the capacitance of your original cap to see if it is still within specs. Some schematics will list the capacitor range.
A smaller gang is for the oscillator section the larger gang is for the antenna
Hi, thank you for teaching me!!!
now we have the video!! :)
Just got my electric screw driver out to have a tweek at the cap on a 1960 valve domestic radio, 5hanks.
@@giulioluzzardi7632 I always like to add that the amps and voltages in antique electrics can be lethal. You can get plastic screwdrivers to adjust caps. And always unplug and ground power caps before working on a chassis.
Mr. Richter can you give a main use of the tuning capacitor into the tuner section
Wonderful presentation Sir. However I have a old model 5 pin tuning capacitor. What is its pin configuration and how to connect it with the circuit, if I want to make a old model transistor set.
Many thanks!
For a 2-gang rated 12 - 495 pF, with 2 lugs on each gang, if I connect all 4 lugs, would that make capacitance 24 - 990 pF? I wasn't aware that antenna gets hooked up to chassis lug. Thanks.
I can't comment on your specific tuner. The one in the video is an AM tuner only. Some tuners are for both AM and FM radios. When you say 2 gang I suspect it is a AM/FM tuner with a gang for each modulation. The tuner, of from the 60s or before, has an air capacitor and a small ceramic capacitor for each gang. The ceramic cap is of a set standard value. It is hooked in series with its metal air cap gang. Hooking caps in series and in parallel have two different outcomes. I can't remember which is which. But I think hooking caps in series increases the overall capacitance while hooking in parallel decreases the capacitance. I could have that backwards. Any way I dont work on FM radios. But I suspect you would not connect the separate ceramic caps together. But that's just based on the seat of my pants. Best to ask another youtuber who works on AM/FM radios.
@@johnallenrichter This is AM only; the dual gang reaches lower frequencies than the cheap 223 pF variable caps, plus it's way cooler. I'm attempting a BC548 3-transistor receiver with hand wound coil, crystal earphone etc. My earphone gets a crackle, otherwise I'm stuck. I was testing the capacitance of connected gangs today and seeing values around 1000 pF on the high end, so that sounds right (lower frequencies). Perhaps I'll put a video of my progress and ask you to check it out, if you would. Thanks again, Paul
@@p1nesap I'd like to see that. Is this a crystal radio?
Thank you sir !
Thank you!
Hey, thanks for getting back to me.
I see, in a radio the capacitor IS completely isolated from the chassis. But the case, the rotor and the shaft are electrically the same point and they are collectively the opposite side of the capacitor from the antenna's input to the stator plates ... correct? And therefore, control over the shaft movement must be done through an insulator ... correct?
I'm planning on using a matching pair to trim capacitance at the input to a record player's moving magnet cartridge amplifier. The standard impedance is usually right around 200pF 47K ohms. Some amps have a few steps you can choose from but the steps are entirely too large ... making those steps basically a gimmick or for some exotic cartridge. I'd like to trim by about +/- 50pF from the standard. I have about 50 cartridges to work with ... it should be educational and perhaps even find each ones sweetest spot.
Whatchya think?
As for AA5 tube radios, I believe the standard then was to isolate the stator from the chassis ground. I have only repaired about 20 of them and in all cases the tuner was isolated from chassis ground. However, i am not an engineer, nor do i recommend that anyone who is not familiar with electrical appliances from that era attempt to repair them. They have enough current to stop the human heart. This Wikipedia article might help you better understand the variable caps..
en.wikipedia.org/wiki/Variable_capacitor
As for your idea, absolutely! You can use two variable caps to arrive at a desired capacitance. In fact the tuning cap itself generally uses static mica cap(s) which allow the tuner's overall capacitance to be finely tuned specifically for a specific frequency range. Be aware of your caps ranges though. You can measure the low end and high end of the range of each cap to establish if achieving your desired capacitance is possible. For example, your tuning caps may have a range of 80 to 350 picofarad for example. And then remember hooking the 2 caps ins series will lower the overall capacitance to less than either of the caps individually while hooking them in parallel then the total capacitance is the sum of both cap ranges. I like your idea of experimenting with capacitance for specific electrical pickups sensors, which you know are actually tiny little ac generators. I personally have an obsession with magnetics so yes, any thing like your experiment is fascinating to me.
thanks man
Soooo ...... the rotor (rotor plates, rotor shaft and frame .... IS the minus side .. and .. IS ground. Is this correct? And rotor plates actually make continuity (their electrical path for current to them) through those little spring washers/holders and through the associated grease. Is that right? If not, how does current get to those rotor plates reliably?
That's the part I'm not understanding ..... because .. I have actually found another use for them other than a radio .... and I don't yet own a capacitance checker. And it's not as a paper weight ; ) Go ahead .. ask me what I'm gonna use it for. Cuz it absolutely blows me away that nobody else that I can find has ever used them this way.
Well, yes! I want to know what you are planning with it. I love things that people create outside the normal box thinking. As for your "minus" connection question - it's way more complicated than what my simple video explained. The tuner cap is NOT connected to chassis ground in any way. Although the tuner is usually physically attached to the chassis you should see rubber insulators on those bolts to prevent connection to the chassis ground - which could actually be hot on older radios. Further, the radio signal being induced by the antenna is an AC signal, not a DC signal. So the signal current is alternating and remains alternating through the radios different stages. So there is no distinct positive or negative sides to the tuner cap when it is being used as an antique radio cap. The variable capacity is tuned to isolate the desired radio frequency within the tuning tank circuit, which this simple video does not get into.
nice vid
I’m a complete novice to this stuff. Still, I would like to use a tuning capacitor in a small circuit so, which is the ground and where do I connect the power/signal, is the stator the ground, and the rotor the input, or vice versa? Please let me know. I want to learn. Thank you kindly
What kind of circuit do you want to build? The best way to understand a radio frequency tuner is to decipher it as a very simple adjustable capacitor. The capacitance is very small. I don't recall off the top of my head but I think it's around 20 picofarad to just under 200 picofarad for most old tube radios. Allamericanfiveradio has a video explaining tank circuits. You should watch that. Tank circuits, or LC circuits are how the tuner works in circuit. L stands for coil and C stands for capacitor. It adjusts the capacitance on the antenna, which is called a coil, to "tune" the antenna to a single frequency. Or perhaps better said it enables the input to be pulled from the antenna as a single frequency. The antenna itself is still being bombarded with dozens or hundreds of different EM frequencies. But we only need one of those frequencies for AM radio to tune in to a particular station. Theoretically we could hook up 100 different tuning circuits to the same antenna wire and pull 100 different frequencies off of it. I always thought that this idea could become an improvement to a vehicle's wiring system - to have a single wire that carries a couple of dozen low voltage frequencies instead of running a separate power wires to every point in the car that needs it. For example, run a 20 amp single wire to loop through and to all the vehicles lights. When the driver steps on the brake the brake switch would turn on a signal generator to infuse the power line with a particular high frequency. Back in the tail light assembly will be a receiving circuit just waiting for that exact frequency to come onto the power cable. When it recognizes the frequency it then takes voltage from the power cable through an h-bridge or relay to turn on the brake bulb. So instead of running 30 power lines to every light bulb in the car we would only need one. So you can see how understanding technology from 70 years ago can help spark new technology today. Good luck with your project.
@@johnallenrichter I was thinking of using it, in an Atari Punk Console, that I built. And since experimentation is a real component, in APC building and I have two of these tuning caps, I figured I’d try but unlike electrolytic caps, this thing has no visible connection points. That’s where you come in. Anyhoo, thanks for replying. I really appreciate it. Cheers!
thanks!
I realize when I watch these type of videos that they are very intriguing but I know nothing.
That was difficult for me to figure out too. Thats why I made this video, simply to pass along something that took me a lot of research and help from more experienced technicians than myself. This video is as simple as my mind can make it. I would suggest allameticanfiveradios for really good advice from a very wonderful teacher and lifelong engineer who is a much better explainer than I am.
sir can you give definition on what is a tuning capacitor. i really need it for my assignment. hoping for your response. thank you
Of signal tracing coming?
can hook up some wires to the var. cap, to show how it's hooked up, where do the wires go on the actual capacitor
Stanley, the wires connected to a tuning capacitor are connected to two different parts: The rotor directly and the stator through the small ceramic capacitor. Your will show you which wire goes to which point on the tuning capacitor.
Cool
Do you know which one of the two capacitors (small or large) has high frequency, either VHF or UHF, I still request you hook up those Rotor and stator to so me wires that are color coded we we viewers can see, I appreciate your explanation but it should have green/blue/red wires to show what is going ware not just nration with the diagram of the schematic. it's hard to understand from that diagram symbol which which rotor is the big and and which rotor is small
First of all I apologize for not seeing your message earlier. The air cap depicted in this video is for an AM radio from around 1950. The cap you ate talking about is for a television. I don't work on old TVs because they have extremely high voltage flyback transformers that can kill a novice in a matter of seconds. I do not recommend anyone, novice or expert, play around with old CRT tube TVs. Especially if you need to ask questions about what the schematic should be able to tell you. Safety is always first.
Can the mica.cap in the tunning capacitor ever go bad
Unlikely. The pure mica cap in tuning caps are pretty solid. Old transformers, like the I.F. transformers used very thin mica wafers with silver foil from the late 1950s and 60s. They sometimes go bad because voltage would jump across the air gaps causing sparks. The sparks in turn would eventually burn a conduit across both sides of the air gap, leaving the I.F. transformer useless. Symptoms are crackling and scratching output. The only solution is to take it apart, remove the mica and silver foil, and bridge a modern cap across it, maybe a 700 nanofarad? Don't quote me on that. Might be 120n. I have a video showing how to fix it. It's called SMD, OR SILVER MICA DISEASE OF OLD RADIOS. Maybe it started when the powerline fluctuated greatly like maybe getting struck by lightning. Or it could just be poor engineering.
John Richter
goodnight my name is Ronny Brenes of Costa Rica I want to make a homemade antenna tuner but I have capacitors as video and occupied capacitors for this application can help calculate 2 x 100 pf and 100 pf single x
It is possible to tune an antenna to one particular station. Es possible cambiar condensador a unica frequencia. Some radio stations back in the 1960s had promotional transistor radios that would only play their single station. The variable capacitor can change its capacitance to tune the antenna to one of several frequencies being picked up by the antenna. Remember, the antenna has all available frequencies on it at every instant. La antenna tengo todos frequencias en tu área. The variable capacitor allows the radio to "tune" into frequencia unica. Perro todos otros frequencia seguir en la antenna. You can use a radio with a variable capacitor to tune into a local station. After tuning in turn off power and measure the capacitance of the tuner with a capacitor tester. This is the capacitance required to tune that particular antenna to that particular station at that particular location. For example, let's say the capacitance is 42 picoFarad. Now tu can replace the the large variable capacitor with a small adjustable capacitor that is able to adjust between 38 piccard and 50 picofarad. Or perhaps along with a finer capacitor that can adjust from zero to 1 picoFarad for fine tuning. I can't recall right now if the two capacitors would be in series or parallel but that is easy to find on google. Once you fine tune the capacitors into the single channel you can "lock" the capacitors by putting drops of hot glue or super glue on them. And now the radio will only play the one station.
That's not true the red ones are the Tremors they're stationary the one with the dotted line shows the mechanical gang of the two air capacitors
Comment in my comment pls...