Capacitors, DC, AC, and Frequencies

[ducklandwikeno]

Cool radio you have .

[sloppyoscar]

Ok. Great video! but one thing .. I believe the audio frequencies will not go through the smaller capacitor -- the 150pF -- because smaller cap values equal higher capacitive reactance (resistance) .. but why would the radio frequency favor the smaller capacitor (and go to ground)? Wouldn't it still favor the larger cap? After all, raising the frequency from audio to radio levels would lower capacitive reactance offered in both caps, wouldn't it? Hope I'm making sense here. Tha nks

[AllAmericanFiveRadio]

@sloppyoscar

In a circuit usually the 150pf is used to drain off the unwanted RF from an audio signal. This 150pf is connected to ground which is a much bigger draw for the RF than is a high impedance grid.

[thebteam300]

this vid was made in 08 april, and they are talking about econimy going down

[TheNeurall]

im wondering, how many people digin in these things today, as a kid i was crazy for this things lol

Having fire and explosions in my room was totaly normal and expected... lol

[AllAmericanFiveRadio]

Thanks TheNeurall

I know I tore apart a lot of stuff when I was a kid.

[AllAmericanFiveRadio]

@23ericiscool

Thanks I'm glad you found the information useful.

[iorixs]

thanks very educational

[AllAmericanFiveRadio]

Thanks iorixs

[AllAmericanFiveRadio]

@ashleshamy

lol, it is in my YouTube to do list.

[ivionday]

"1 dot 21 jigawatts!!" nice video.

[bing434]

Really informative video, thanks for sharing.

[AllAmericanFiveRadio]

Thanks bing434

[ashleshamy]

@AllAmericanFiveRadio why will the capacitor block dc and allow the ac ....justify !!!

[frostwow]

great vid

[AllAmericanFiveRadio]

Thanks.

[JoeyMars1]

Excellent! I have read many books on this stuff and no-one I had found yet explains it in detail! Thanks for considering the point of view of the beginner.The questions beginners would arise are usualy by passed and un-answed in other books. I would certainly buy your books if you wrote one! I watching all you videos..

[1938Silvertone]

What's your recommendation on Signal tracers and Oscilloscopes? I've got a Crosley 66CA with low voltage on pin 6 on the 6SQ7 with no audio output, but all other voltages on all the other tubes are good. What should I look for? Only equipment I have so far is a Simpson vtvm.

[AllAmericanFiveRadio]

Check resistor 7. You can build a signal trace, I did a video on it. The oscilloscope should be 5Mhz for amplifier and AM radio. 20 MHz for AM, FM, and TV. These are minimum frequencies, if you can get a scope 20MHz and up, that would cover must antique equipment.

[1938Silvertone]

Hey Rick, Thanks for the tip. I've been studying that resistor 7 on the schematic, and can't seem to get a reading on the meter?? Not sure I know how to measure it though. And I'll be to watch the video.

Dave in Wilson, NC

[amartinjoe]

thanks so much for uploading this; I am studying to be an electromechanics technician; it's an online course but the materials don't contain enough photos or even videos of the items discussed.

this is so helpful. thanks!

[AllAmericanFiveRadio]

That's great! I'm glad the video helped. THANKS AGAIN.

[gmcjetpilot]

Rick your video helped me with a "Re-Cap" issue I struggled with, a "Mystery-Cap", three leg ceramic (but not in schematic?). The center leg is grounded. The other two legs go to the 35C5 Tube (audio out), one leg to pin-6 Grid #2 and the other to pin-4 heater. This same Cap (printed on cap part 22-24 ) is shown across the AC line-in, resolving it's a 0.0047 500V.

My confusion, WHAT FOR? Thanks to you I know, a RF filter. It's on both radios (Y832 Zenith), so it's not a mod or mistake.

[gmcjetpilot]

All this time I thought I knew how capacitors worked in different applications, but not until you explained it, showed the oscilloscope and the relationship to DC/AC and RF/Audio stage of this radio did it really sink in. Thanks for explaining. Simple but critical idea to RF/Audio and widely misunderstood (by me at least). This really helps with my current tube radio restoration.

[AllAmericanFiveRadio]

THANKS

[comateensnyc]

Rick - In this video you show how C14 will block audio and pass RF, while C15 will pass both audio AND RF.

My question is this: Why does the RF component "choose" to go only through C14 to ground, if it can pass equally well through both capacitors ? Why does it not go directly through C15 to the grid, or more to the point, through both of them, thereby leaving the audio still contaminated with an RF signal ? How is this circuit able to filter the RF off the audio ?

Regards - Nick In NY

[AllAmericanFiveRadio]

Hey Nick, good question. The RF goes through C14 to ground because the ground is a very low impedance return path. And C14 lets only the RF pass through it. If C15 went to ground there, both the audio and RF would go to the ground return path. Another way to say it is the ground through C14 is a much easer path for the RF because the impedance of the grid of the tube is much higher than the ground return path. Rick

[luisgarciaalanis]

Hello Rick,

Complicated to imagine, but lets assume is so and RF gravitates towards C14. What would prevent the audio signal from going through the lower impedance C14path?

Thanks Luis

[AllAmericanFiveRadio]

It has to do with the frequency response of the component. The frequency response of low MFD like capacitor 14 = 150pf, will pass High frequency easily (RF) but almost no Low frequency (audio). That demo starts at 4:03.

[luisgarciaalanis]

Thanks for the info I will read up on frequency responses of components :) I am new to electronics and learning,

[AllAmericanFiveRadio]

Don't worry about trying to learn it all at once. Read some and think about for awhile and then read it again. Sometimes it took me many times to get an idea.

I did a video on the Navy Electronic Courses and I put them on my server so they can be downloaded. There are 24 of them and they are all excellent and free.

[comateensnyc]

Rick, I see, thank you for your reply! Can we then say that R13 impedes the audio signal sufficiently for it to activate the grid of the 50L6 before it returns to ground after R13? Is the ground after R13 the return path of the audio signal ?

[comateensnyc]

AAFR - Thanks so much for these splendid videos.

What is confusing me about this example is the purpose of C15. If C14 is grounding off the RF, then what is C15 doing ? Why is it needed?

Regards from New York

Nick

[AllAmericanFiveRadio]

Hey Nick,

After C14 (150pf) grounds out the unwanted RF what is left on that wire is the audio signal and C15 (0.01mf) is a high enough capacitance to pass this audio signal to the control grid of the 50L6 which amplifies it and drives the speaker. C15 also blocks the positive 66VDC from the 12SQ7's plate getting onto the control grid of the 50L6 and only allows the audio signal to pass through to it. So C15 is doing two jobs at the same time.

Regards from North Carolina

Rick

[comateensnyc]

I see, Rick, thanks so much, it's great to talk to you. Your videos are just terrific !

Could we argue that the only purpose for C15 there is to block the DC plate voltage, as the audio signal would reach the grid whether or not the capacitor was there ? I mean, the cap is not necessary to transmit the audio to the grid, is it ? It would not be there if there was no DC plate voltage present ?

Thanks so much for your patience Rick; I'm only just beginning to get a handle on this stuff.

Nick

[AllAmericanFiveRadio]

One thing to keep in mind is that capacitors block dc and allow ac to pass through. Audio is an ac voltage so C15 allows this ac audio signal to pass through it to the control grid of the 50L6. There is no other possible path for the audio. If you took C15 out of the circuit there would be no audio output.

[eufaula1]

These videos are great!! You really need to do more of these, or even think about selling a DVD. Excellent material.

[AllAmericanFiveRadio]

Thanks! I'm working on a few ideas and I'm getting some ideas form other YouTubers. I may make a DVD for sale when my electronic videos can fill one up, 4.5G. It would be more covenant for the viewer and the viewing quality would be better.

[BassmasterBling]

Thanks for the great educational videos!

It sounds like you are using a very high quality microphone for your narration.

[AllAmericanFiveRadio]

Thanks!

On this video I used a small head microphone and the microphone on the video recorder. Switching the sound helps keeps the ear interested. On the last AM Transmitter video I used both again. But in about the middle when I'm talking for a long time with the head microphone, I added a sound track of Janis Ian singing "At Seventeen". Again to help keep the ear interested. I reviewed the video and it seemed to work so I left it in.

[Hammondlover2]

Thank you, you've turned a light on for me!

[AllAmericanFiveRadio]

Thanks, hope it helps.

[joernone]

Rick,

Really good stuff. Clear as a bell. Great job.

I know how much preparation, time and effort it takes to put these videos together. It's very much appreciated. Thank you.

Best regards,

John

p.s. Continued bad luck with the Airline, but I'm still in the game.

[AllAmericanFiveRadio]

Thanks John

Hope the Airline straightens out soon.

Rick

[radioam232]

Very convincing demonstration and neat thing to use the two channels in this way! I knew the effects but this is the perfact way to demonstrate.

[AllAmericanFiveRadio]

I rarely use both channels of my scope at the same time. But I was thinking about how to best show the effect of different AC frequencies traveling through capacitors of different MF's. I did some experimenting and testing, and it worked great. THANKS!

[CameramanLink]

I never knew what that small capacitor was for coming off the plate of the AF amp. And now I know! Good job with the demonstration!

[AllAmericanFiveRadio]

There's more going on with there than what you would think. I'm glad you found the video useful. And thanks.

[Organgrinder010]

Very nice feature here, some good points made. Splendid job!

[AllAmericanFiveRadio]

Thanks. That small part of the circuit does not look impressive, but there's a lot going on with those few parts.

[AllAmericanFiveRadio]

Thanks.

Yep, I've been thinking about it.

[mariopica]

I will be waiting excited to watch you collection !

[vinylman86]

where did you get my radio from, lol! anyway i hope you get the matching 45 player for it. oh yeah, i recapped it, but i have to redo it.

[AllAmericanFiveRadio]

That would be really great to have a matching player. As you saw in the video I have not recapped it, but someone else did do a little work on it.

[jefferyb304]

Fine info here. It seems that form of speaker grille on the radio would greatly amplify sound from the speaker.

[AllAmericanFiveRadio]

Thanks.

It is a neat looking RADIO! And it is loud. I have seen it in some old B&W science fiction movies.