How to Play Old Music on a Vintage AM Radio Using a Low Power Broadcaster

[@guglielmomarconi9942]

At the time of publication of this video I had been looking into setting up a local broadcaster for transmission of my favorite music around the house. This project fitted my requirements exactly. I've now built a couple of these units to identical board layouts as in the video. They all work very well indeed and I am able to hear my favorite music on various a.m. band radios around the house. I use a metal bed frame as the antenna which gives great reception around the house. I plan to make checks in the local area to make certain that the signal is not reaching too far outside my boundary. The circuit seems to run happily at around 5 volts, so I can power it from a USB socket on my computer. Many thanks for sharing this design.

[@VintageElectronicsGeek]

Great work Don! I appreciate old school...no arduinos! :) ~Jack, VEG

[@RestoreOldRadios]

Thanks Jack. Believe or not I have an Arduino project on the horizon. LOL Best, Don

[@Backtothefutureradios]

Another great project Don! Great sound really rich! Take care--Larry

[@1mctous]

"Just One More Chance" played in the first segment, but I'd give this AM transmitter many more chances to play.

[@tectalabyss]

Hello Don. Sorry to be so late. Still getting things sorted at home. All my best and have a very Merry Christmas and a Happy New Year. Bobby

[@wendelljackson1488]

I've finished the AM Broadcaster, pretty much according to your design. I find that I get a bit less signal distortion by adding a base-to-ground bias resistor in the audio amplifier circuit. I also added the suggested capacitance on the power input section for which I am using a 12V linear wall wart. Everything works great! Thanks for a good plan.

[@RestoreOldRadios]

Wendell - glad it came together and works well for you. For my edification, what value resistor did you add in the audio section? Best, Don

[@wendelljackson1488]

@@RestoreOldRadios I added 150K from the base to negative rail.

[@wendelljackson1488]

Don, I should also add that I rewired the 750K resistor from the base of the audio amp directly to the positive rail instead of through the 22K on the collector. (A result of modeling on a circuit simulation app.)

[@RestoreOldRadios]

Thanks for the feedback Wendell, much appreciated. Best, Don

[@audioreparaciones8956]

Hello, Don. Thank you very much for the nice video. I followed your design as closely as I could and it sort of works. It is modulating the frequency instead of amplitude. I checked the circuit many times already. Can you give me some clues? Thanks in advance and warm regards

[@RestoreOldRadios]

Thanks for reaching out. This was a very early design for me that I no longer use and the modulation technique is not good; more of a superimposed audio on the carrier wave. You may find this page helpful at: www.geocities.ws/raiu_harrison/mwa/tech/circuits/modulators.html and check out my later builds at my playlist: AM Broadcaster kzbin.info/aero/PLjLu4V-71S1Kaz5Eiw0Cx5c8U0DWll87B Reference the video descriptions for a link to the schematics. I hope this helps. Best, Don

[@audioreparaciones8956]

@@RestoreOldRadios Thank you for the response. Maybe i can save the amplifier stages and change the oscillator. I'm having so much fun with this. Thanks for the links too, you are very kind. Regards!

[@GeorgeChristofi]

Ok Don... I finally got mine built and working. I have gone old school in my build though! Video is on my channel.

[@RestoreOldRadios]

George - I’m eager to check out your channel. Hope to visit later on today. Thanks again. Best, Don

[@RestoreOldRadios]

George - I had an opportunity to watch your old school build of the Tx. That was very cool the way you laid it out. I’ve never done one that way and found it very interesting to watch. Thanks for sharing. Best, Don

[@GeorgeChristofi]

Many thanks Don, glad you found it interesting. I first started out by doing the copper nail thing as a kid and I just thought it would be an interesting way to this. I find it allows people to learn about the different stages in the build and could even be made modular so you build an audio stage on a square, then an oscillator etc, bit like the block diagram.

[@janetwinslow2039]

How much FMing occurs when applying modulation the the oscillator?

[@skycarl]

Nice design. Thanks for sharing.

[@RestoreOldRadios]

Thank you Carl. So far so good. I’m playing some oldies as I type this. Best, Don

[@ianbutler1983]

Thanks, great video as always.

[@RestoreOldRadios]

I appreciate it Ian. I have a Zenith restoration coming soon. Thanks for following my channel. Best, Don

[@AMStationEngineer]

I've seen schematics for avionics that weren't this perfect, and I'm talking CAD drawn items, geeze - Don, how do you get these so perfect; draftsman tendencies?

[@ordinaryaverageguy76]

I'm currently looking into such a thing to provide program material to some WWII era radios as working parts of a museum display. Too many suggested circuits are based on misusing fixed freq xtal oscillator cans. So, if you have the time, I have a few questions to help me to my goal. Thanks!! 1. How is this design for generating harmonics? 2. You said L1 & L2 were wound in opposite directions but it appears they are wound in the same directions, aren't they? Both appear righthand turns. So, it's functionally a single centertap winding, right? 3. What led to choosing Hartley vs Colpitts? Was that simply a fallout from beginning with the Buckwalter book schematic? I was thinking it might be easier for parts cost to use a single slug-tuned coil with two fixed caps instead?

[@RestoreOldRadios]

Thanks for watching and your questions. Regarding harmonics, like many LC oscillators I can tune the transmitter to 600kc and detect the signal on my receiver at 1200kc at a decreased level. Unfortunately, I don’t have a spectrum analyzer to measure the amplitude of the harmonics. The two coils are in opposite directions. One winding is over the top while the other is under. Hope this helps. The decision on the Hartley was just parts I had on hand. It’s my understanding the Colpitts is more stable. If you're considering a fixed frequency oscillator, you may consider a modified Colpitts or a Butler using a crystal. A few links below for reference that you may have already bookmarked. www.circuitstoday.com/lc-oscillators-and-types www.electronics-tutorials.ws/oscillator/crystal.html bgaudioclub.org/uploads/docs/Crystal_Oscillator_Circuits_Krieger_Matthys.pdf www.rfcec.com/RFCEC/Section-2%20-%20Fundamentals%20of%20Electronics/09%20-%20OSCILLATORS/ Good luck on your build. Best, Don

[@ordinaryaverageguy76]

Thanks for the info & links! By the way, here's 2 reasons why I think those 2 wires are wound in same direction. 1. In an LC tank the current flows thru the inductor & back every RF cycle. If the inductor is two windings in opposite directions the 2 mag fields are opposing & cancel & there's zero net inductance. 2. The continuation of the upper wire wraps the core the same way that the lower wire does. I can send a pic "with lines and arrows" if you wish. :-) In detail: If you imagine continuing to wind with the left end of the upper of the 2 wires in the video, the next thing it will do is pass downward & then under the core & then come up thru the center (just like the lower wire already does). Next it would go down on the outside again, under again, and up thru the center again (just like lower wire does) & continue onward that way along the core in a CCW direction (like the lower wire does). The ending of the final turn would come up thru the center just as the lower wire's right end does. They both spiral like righthand threads do.

[@GeorgeChristofi]

Don, I'm a touch confused here. Looking at the toroid part of the video it conflicts with what you are saying re diagram with the actual winding. The toroid in the video at 2:15 is wound in phase, if you join either one of the sides together the direction doesn't reverse in the winding yet the diagram shows antiphase. If you put two coils on a toroid in antiphase then they cancel each other out because when one side is high, the other is low. Or am I missing something major here? I wound a toroid in antiphase and effectively got zero end to end but 100uH in each side. winding it in phase, I got the required 180uh value. Is it just my stupidity and I'm making a rookie mistake?

[@guglielmomarconi9942]

+George Christofi. I wound the coils as they appear in the flesh (photo) and the oscillator works well. I have not tried to wind the coils in reverse direction with respect to each other. I may try that though to see what results I get.

[@GeorgeChristofi]

@@guglielmomarconi9942 Thats what I thought. Don's coil in the video is just a standard coil with a centre tap, not an antiphase one.

[@rivards1]

Can you add a link to printable verson of the schematics, please?

[@RestoreOldRadios]

Sure thing. Send me an email to TheRadioRepairGuy at gmail.com and I’ll forward it. Best, Don