I finally think I'll like radios. I always liked and fixed amplifiers but I had radio dislike. I believe for lack of knowledge. Thank you Tony. I watch your videos from Brazil.
Thank you very much also. I learned this almost fifty years ago but unfortunately gave back to my precious teacher. Is so nice to relearn this and be able to rewind when there is moments of confusion. And again for you in taking the time to format and present in a understandable way, much appreciation. Ps. Wish we could find where and when, you resell these repaired items. Best ...
Thank you for the comment! When I post things for sale on eBay, it will be under the account of barbandtonyb. I have several items that will be going up in the next month or two.
xraytonyb, Thanks for sharing this information. I've been looking for information of FM modulation theory, to better understand what is actually happening. I see that it is indeed a bit more complicated than AM. I suspect that any type of old tube FM radio could be very difficult to align and tune. For now maybe I will stick with the AM radios, until I get a better understanding of all that is involved in FM. I am just now beginning my quest into Radio electronics. Thanks again. Jay
So is the (-R) signal obtained at the station by inverting the (R) signal 180 degrees with an inverting op-amp (with a gain of -1) then adding the (-R) output signal (with the same amplitude as the (R) signal) to the (L) signal using the two 1K resistors, then taking the ((-R) + (L)) = ((L) + (-R)) = (L - R) between the resistors? I wonder how the brain would perceive headphones where one side is (L+R) and the other side is (L-R) (?) This stuff went over my head in technical college, but this video is great. Tony makes the complicated simple. I’ll probably watch this video several more times.
Too bad there's no "love button" on RU-vid... I really love this kind of stuff. Explained to everyone's understanding. You can call it "FM multiplex for everyone".
Also SCA stations was used by companies that sold elevator music and ethnic broadcast to paying subscribers. There used to be kits and circuitry to build the receivers to steal these channels advertised on Popular Electronics Magazine in the 60's and 70's.
Very helpful. I'll need to play around with this to really understand it better but it seems to me that to align an FM radio front end one wouldn't need to inject MHz signals into it at all, except to align the dial tracking position. Am I off base here? Most signal generators won't reach those wavelengths. I've been thinking I may have to use the ARB function to capture/create a lesser multiple and multiply it to get up to the FM band. Again I may be off base here too. Any comment from more knowledgeable radio folks than I would be appreciated.
I have two separate questions. Does it mater if the input signal (tuner) and the local oscillator are out of phase one leading or lagging. ( meaning the peak to peaks are in phase or not) and the same question for the stereo sidebands. for them to cancel each other out , would they need to be in phase with each other. This is the confusing part, understanding how they repel each other or cancel each other out. You put out excellent videos, I am just having a problem understanding the mixer and the IF filters. Thanks.
MrMac5150, Thanks for watching! I'm not so sure about the local oscillator/tuner, but as for the MPX signal, phase relationship is critical. The 19kHz pilot tone produced at the radio station is used for frequency as well as phase generation for the rest of the stereo signal. When the tuner "sees" this pilot tone, the MPX circuit locks onto it and uses it for phase and to generate the other frequencies used for the 38kHz DSBSC "L-R" signal. The SX-1050 from the video uses a PLL circuit to keep everything in line.
Oh, I forgot I have a question, can you show us how you hook up your RF Generator to the 300Ω Antenna input with the 300Ω Dummy load? A quick diagram...Its something that isn't exactly that clear in any of the alignment instructions I have read, thank you so much...
What is the colored lugs, some are red, black etc, for tiny transformers for in small radios? And how do you solder them in without burning the wire into, the wire is so thin, like a strand of hair.
awesome video, I learned a lot. Are you able to see the 10.7 MHz signal on a frequency counter? and if so where would you see it at, right after the mixer?
I have the opportunity to purchase a early 50s Olympic record changer radio. it is complete but in unknown condition. the speaker is intact and is an RCA alnico 12". it comes with all the original paperwork including bill of sale and schematics. I'm interested in it as my first venture into tube electronics (with a reasonable amount of knowledge in solid state). It's $40. think I should get it?
Before purchasing, go online and try to see if you could find a schematic or service manual for the model you want to purchase. Nostalgia Air is a good resource. If you find service documents, then go ahead and purchase. If not, I would pass on it and find one that has service information, because its your first tube repair.
