Telefunken Gavotte 55 restoration part 5. Getting rid of the hum, and getting FM back.

The issue of excessive 50Hz hum was not completely resolved in the last video in this series on the Gavotte 55. I was actually at a loss, having thought of all sorts of reasons for its existence, heater supply interference being the primary one. However, it was not the source. It was actually ... no, watch the video :)
The non-existent FM was also awaiting due attention. Here the reason was a lot simpler.
Enjoy the video.
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[@sincerelyyours7538]

Nice troubleshooting on the hum issue. Reminds me of 40 years ago when I was a young bachelor I'd try to impress my date with my new fancy-dancy Blaupunkt car stereo and turn up the volume when a particularly nice song came on the radio. But it would randomly drop into very loud oscillation for no apparent reason making me slam on the brakes and my date bail out at the next corner. Turned out to be caused by a ground-loop between the stereo and its separate amp unit which was located under the dash a foot or two away. A length of 14 gauge wire grounding the two cases together solved the problem -- and restored my reputation as well.

[@electronicsoldandnew]

😊

[@preiter20]

These old German tube radios are works of art.

[@electronicsoldandnew]

👍

[@waynio67]

It’s the weekend, means another electronics old and new video! 👍👍

[@electronicsoldandnew]

You may a double before this weekend is over 😊

[@chrisclark6192]

Hello again. I'm glad to see that you are doing well with this lovely radio. The symptoms of a grounding issue can be a real problem to trace. But more often than not, the cure is quite often a quick easy fix. The push button issue may be a problem if the contact cleaner does not work. As usual I'm really enjoying this series and can't wait to see the end result. Stay safe and well. Cheers Chris.

[@electronicsoldandnew]

Thanks Chris. The hunt continues 😊

[@williamchow1624]

Well grounded, BRILLANT!

[@electronicsoldandnew]

👌

[@72notout13]

Great job again, and the station dial glass is a real work of art.

[@electronicsoldandnew]

👍

[@paulp2089]

Its looking good Manuel.

[@electronicsoldandnew]

👍

[@DerekHerbst747]

That's a handy little tric for isolating bad grounds. Thanks! :)

[@electronicsoldandnew]

One has to get creative when you get desperate 😊

[@geirendre]

@11:00 That's why we had a small piece of folded paper laying next to the radio, to jam between the key and the glass behind to make it play. :-) It wasn't a Telefunkern or Grundig, but it had the same piano keys with bad contacts on. Looking forward to seeing it al put together. Nice set and great job.

[@electronicsoldandnew]

Thanks. Maybe a piece of paper will be needed here too 😊

[@saarike]

Thanks a lot for great video!

[@electronicsoldandnew]

pleasure

[@alfredneumann4692]

Now, is this 'ground is not ground-error' a constrution error or really an error in mounting the tube-socket? The designer should have heard this hum within a test. What i have learned, when you have much ground points, use ONE point like a star. And you will not get loop-hum. Very good example video.

[@electronicsoldandnew]

I think the problem with the tube socket is a result of corrosion in the socket-chassis connection, so it probably did not exist when the radio was newer. These radios never follow the star ground system, unfortunately. As I also work with hifi amps, I’m a great defender on the system.

[@radiotvrepair1059]

Thanks for this vedio

[@electronicsoldandnew]

pleasure

[@kennethiman2691]

Looking forward to how you fix the switch. A cliffhanger for sure. Finding a replacement might be difficult.

[@electronicsoldandnew]

practically impossible to replace. But could be something really simple.

[@jdmccorful]

Contact latching?

[@danielsaturnino5715]

I was going to ask about bluetooth but I dont think the museum would apreciate it.

[@electronicsoldandnew]

😊 I’ll leave this one as original as possiblez

[@electronicsoldandnew]

😊 I’ll leave this one as original as possible.

[@piwex69]

Beautiful work as always. Shouldn't the magic eye be rotated to face the closing bar (top-down light straight)? It looks slanted right now.

[@electronicsoldandnew]

No, this one is pointed down which actually makes it more visible.

[@jazzncofee3871]

Amazing! How did you find the root cause very well??!!!!!

[@electronicsoldandnew]

It’s been quite a while since I did that one 😊

[@peterhaan9068]

I looked at the other comments but nobody asked this specifically, did you in fact ground the other questionable ground that you used to prove your ground problem theory? Hated working on most of these European designed/built radios. When they worked they were often better than most of the US made home market radios but when they didn't... Got around the frequent failure of "piano" switches on these radios by kludging in a micro switch(s) to replace the failed contact(s). Cleaning rarely worked more than a couple of months.

[@electronicsoldandnew]

The other failing ground point was in fact on the same tube socket, so grounding the socket took care of that. I have become quite used to working on german sets, and have not had the pleasure of restoring a US radio. The german sets are more abundant in my part of the world (Madeira, Portugal).

[@mackfisher4487]

What's the chances are you doing a short video showing off your radio collection?

[@electronicsoldandnew]

I have radios spread out all over the place. Some at home, at the office, a friend’s studio, etc. My satisfaction does not come from owning them, but rather from restoring them. I then like to see them used, and in this way they get some play time daily.