Do we have FM, and how does it work? - Tube Radio Restoration Back to Basics part 9

For me, FM is the most important band on these German tube radios. The quality of the sound and the availability of local stations, make it a must-have feature for me to purchase a radio for restoration.
This band can be a little challenging if it doesn't work, but a thorough understanding of its theory goes a long way to making any fault-finding easier. Let's get to it!
I hope you enjoy the series, and invite you to comment.
🎥 Other videos in this series:
■ Back to Basics 1 - Tube Radio Anatomy: • The Parts That Make Up...
■ Back to Basics 2 - Tube Radio Anatomy: • Checking the Power Sup...
■ Back to Basics 3 - Follow the B+: • How to Check the B+ Sa...
■ Back to Basics 4 - Testing the power output: • How To Check the Power...
■ Back to Basics 5 - How to safely test the output tube: • How to safely test the...
■ Back to Basics 6 - Preamp, Tone Shaping and of lots of detail: • Preamp, Tone Shaping a...
■ Back to Basics 7 - What do those tone presets really look like?: • What do those Tone Pre...
■ Back to Basics 8 - We've got LW and SW, but where is the MW?: • We've got LW and SW, b...
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[@tanveernaeem1157]

Another great educational video. Love the way you isolate/erase the non concerning sections of the schematic which makes schematic clean and easy to understand. Must admit you are not only dextrous in what you do, but also a brilliant teacher. Thanks for sharing your knowledge and keep up the good work of creating this one of a kind KZbin content.

[@electronicsoldandnew]

My pleasure

[@kilcar]

Great FM video tutorial! Now , I hope we can hear you play those guitars! I built a VOX Jaguar Heathkit combo organ in high school in 1969, which planted the seed of interest in electronics. Iyour turtorials are immensely interesting and informative. Thanks for all you do from us in Bend, Oregon, USA

[@DavidTipton101]

So much effort in doing the circuit drawing clean up Manuel, kudos 👍 It takes some experience to get one's head around the ratio detector and how it works. In reality, you only need to be able to understand what it's doing and how to set it up. I learn a bit more each time I do one, I expect to learn more when I see you do the FM alignment. 👍🙂

[@electronicsoldandnew]

The cleanup is part of the routine that I actually find very relaxing 😊 I read a description recently about a different type of detector, and the author said, “if you can’t understand the theory, look at it as you would an IC”. Made a lot of sense 😊

[@erikdenhouter]

FM ratio detector, layman's explanation, that's all I have: when you observe the bode plot, the graph for the frequency response of the 10.7 filter(s), you will see a mountain top, and on both side the flanks decreasing. That means that a deviation from 10.7 MHz will give a decreasing amplitude. So when you use the flanks (the part as linear as possible), the amplitude (the Voltage output) is somehow proportional to the deviation from 10.7. In that way they change frequency deviation into Voltage fluctuation, hence sound.

[@electronicsoldandnew]

That is a great explanation 👍

[@robturner3065]

That was a great walk-through of a practical fm schematic. In the simplification process it would have been nice to replace the eabc80 with a couple of diodes for clarity. The din symbol for all those diodes with little blobs for cathodes can be hard to get your head round

[@electronicsoldandnew]

👍

[@DavidSmith-zx7wz]

Great content! Really helps us learn. Thanks

[@electronicsoldandnew]

Pleasure

[@tubeDude48]

Well done, my friend! 👍 Unless you have covered this in the past, (can't remember); you might want to go over tube designation. i.e., in the US, a 12AX7 would mean the 12 stands for a 12 volt tube, the AX would be the manufactures designation, and the 7 means there are 7 elements inside the tube.

[@electronicsoldandnew]

👍

[@IainDavies-z2l]

We have had FM since the early 50s, if you don't know how it works now you never will. Perhaps you can tell us the joys of 405 line TV next.

[@electronicsoldandnew]

TV is definitely not in my plans 😊

[@robturner3065]

I listened to FM radio this afternoon. Last time anyone watched 405 line TV Tiswas was still on...

[@electronicsoldandnew]

😊

[@ralphj4012]

Educational, as always. Though, saying anode, when your preference is tube, is not permitted, ho, ho.

[@electronicsoldandnew]

My tubes have anodes, and my valves have plates. I’m a confused Portuguese 😊

[@robturner3065]

​@@electronicsoldandnewlol that's understandable, when I lived in Brazil the valvulas had placas not anodos

[@electronicsoldandnew]

😊

[@JonRig]

Great vid, as always! I am really enjoying this series!! I have picked up so many useful snippets on every one. I agree with you with regards FM. The German ones seemed to be the first to have it (1950-ish onwards) and those are the ones that interest me. There are some beautiful looking AM-only radios out there but I like to be able to enjoy how they sound and not just look at them!!

[@electronicsoldandnew]

Agreed. I like to restore the AM for the sake of curiosity, but the Fm is really the only band that’s actually useful these days.

[@douro20]

Have you come across any which use a phase detector with a gated beam tube? I know they were more common in television receivers but they were also used in FM radio receivers as well.

[@electronicsoldandnew]

Never had one of those

[@mackfisher4487]

To bad we don't have an internet Bot filter for KZbin

[@electronicsoldandnew]

😊

[@BobAndersson]

Nice one Manuel. But what is it about these radios that induces that faint audio whistle/oscillation between stations on FM? I often hear it and I have yet to understand how to kill it. I'm assuming it's feedback as the intensity usually seems to change as you increase the received frequency. Maybe an instability in the ECC85 FM local oscillator circuit? BTW I'm totally with you on tuning the ratio detector - I was fortunate to pick up a Keithley 2015 meter last year and now I just go for minimum THD. So much easier than fiddling with resistors and microammeters! 🙄

[@electronicsoldandnew]

Those whistles can be tuned out in the front end, but I wouldn’t mess with it if it can be avoided 😊 I’ve been looking for one of those meters, but the prices are a little steep. That is indeed the best way to do it.

[@stephenkelly8156]

I am thinking of getting this portable oscilloscope with a signal generator. Do you think it would be useful to do alignments? FNIRSI DSO153 is the make and model. Love your videos and teaching methods!

[@electronicsoldandnew]

Isn’t that the one that goes up to 200kHz? If so, it won’t work for alignments.

[@stephenkelly8156]

@@electronicsoldandnew AM only?

[@erikdenhouter]

@@stephenkelly8156 Generator is 10KHz max. Only for audio.

[@borismetodiev3218]

Awesome video as always! Don't stop making these videos because they are really helpful for me and for others as well. I've been following your channel for quite some time because I have a tube radio that doesn't work and I am trying to fix it. I've been wondering if you can give me some advice/help me fix my radio. If you are willing to help me, just give me an email or a phone number and I'll leave you a message. Thanks!

[@electronicsoldandnew]

I’m afraid my time is very scarce and I barely have time for my own projects. The best I can do is share some info on these videos and thereby hopefully help you to do it yourself.

[@borismetodiev3218]

@@electronicsoldandnew Okay, I fully understand you because I am actually still at school and I kniw that feeling when your time is limited. I'll be waiting for a restoration of a radio that has the same problem as mine. Thanks for the respone and if you were wondering, my radio is a Rigonda 102 :)

[@danielsaturnino5715]

Very Nice. Thank you

[@electronicsoldandnew]

Pleasure

[@josephmagedanz4070]

Thank you!

[@electronicsoldandnew]

Pleasure