Grundig 3160 tube radio restoration, part 6. Selenium rectifier, filter caps and FM alignment.

The selenium rectifier wasn't changed in the beginning, so it's time to do something about it. The filter caps also need changing. Obviously, a voltage dropping resistor needs to be inserted.
Also, we can't call this radio complete without checking the alignment of the FM IF.
Enjoy, and stay safe.
See the full info for this set at:
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#tuberadios #antiqueradio #radiorestoration
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DIY TEST GEAR: The title says it all:
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RESTORATION BUILDING BLOCKS: A series of videos showing detailed steps used the restoration process of tube equipment:
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HowTo's: Various videos on some simple techniques and projects:
• Extend tube radio FM b...
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[@DavidTipton101]

I have just done the same job on a Nordmende Elektra 58, a selenium rectifier and an AM/FM alignment. I wish I had seen your video first on the FM alignment, I have no experience with FM and your explanation set of a few light bulbs. As always, thank you for explaining what you are doing it is a great help for novices like me. Derek has been a great help to me in the past too, we have the same career background ✈👍🙂 Thank you and cheers!

[@electronicsoldandnew]

Well David, this hobby works on the principle of “bank of favours”. I learnt a heck of a lot from other guys on KZbin, and now enjoy sharing my “mistakes” to help others avoid them :) I dare say that you will be doing the same thing sooner than you think.

[@electronicsoldandnew]

Derek was actually in Madeira on holiday last year. It was a pleasure meeting up with someone with the same interest and a South African at that. Good times.

[@josephpayne4012]

I watched and enjoyed this series. I am currently restoring a Grundig SO 260 stereo Console receive and the videos are very helpful. Thanks!

[@electronicsoldandnew]

my pleasure

[@kevinatkins7641]

I've really been enjoying this series, great work. I've got a 3028 'Marlborough' model, which I inherited about 30 years ago from a great aunt. Now 60+ years old, it's never seen the inside of a workshop and is still going (still used regularly), although I think now it could probably do with a refurb - new capacitors etc. It sounds great, so much so that I've also thought about adding Bluetooth to it - I reckon it would trounce most bluetooth speakers / docks on sound.. These are lovely old sets - big kudos to you for doing such a great job with the refurbishment.

[@electronicsoldandnew]

Thanks Kevin. The Bluetooth will definitely trump modern solutions. You should try it.

[@dougmcartin3881]

I've always found over the years that when it comes to FM alignment, the less you touch things the better off you are. If it's working reasonably well leave it be. ATB Doug.

[@electronicsoldandnew]

That's good advice.

[@paulbache3940]

Grundig always made good radios, and you have resurrected a great one,

[@electronicsoldandnew]

I believe so.

[@michaelwoods4426]

Fantastic you have the patience of a saint

[@DavideFabrici]

Wonderful video as always! In the fm alignment section I think Grundig is telling you to set R3 for an IF voltage of 300-400mv so to achieve maximum AM signal rejection. At least that’s what I understood from the text 😁

[@electronicsoldandnew]

I thinks that’s right, but as the reception was great, I decided to leave well enough alone. The little pot is very sensitive and I didn’t want to mess with it at all.

[@DerekHerbst747]

You got lucky! I think we analysed the ratio detector resistor correctly. I'm going to ask Meister Jambo. He's got a great KZbin channel, however it's in German. That's not an issue because you can select closed captioning and choose English.. he's really good and very entertaining.

[@electronicsoldandnew]

I'm going to have a look at his channel. Who knows, maybe I'll even learn a bit of German :)

[@saarike]

Excellent work! Thanks

[@chairuser4]

loving this

[@Gordonseries385]

Thumbs up enjoyed watching stay safe also and take care

[@electronicsoldandnew]

Thank. You too.

[@GeorgeChristofi]

As with all Germans of that era, it sounds fantastic. Looking forward to the cabinet...

[@electronicsoldandnew]

I’m not ... haha

[@schwarzdrossel2454]

Thank you so much for explaining! I searched so long for a propper solution! Many t(h) anks from Germany!

[@electronicsoldandnew]

Pleasure

[@tubeDude48]

Job well done!!!

[@electronicsoldandnew]

Thank you.

[@kevkabluebird1032]

Hmm. Some peeps use a resistor to drop voltage. Others use Z-Diodes (as i do too). Had this "bit too high voltage" problem with one of my radios after removing the selenium rectifier (it was toast). I use 3 Z-Diods (each drops 18 V) and i'm fine. Works like a charm and they don't run too hot.

[@electronicsoldandnew]

Yes, that works well, as long as the power rating is correct.

[@_2N2222]

You showed how to reduce the B+ voltage only by inserting a resistor in series with the rectifier. But this fixes just the VB+ issue, the rest of the radio still runs on overvoltage. With 230V (or more, as you often say is common in Madeira), this is about 5% too high. This stresses the isolation of the transformer, which was built for 220V, but there will be some margin, even in this old device. But also the filament voltage will be 5% too high, and this decreases the life time of the tubes. So I would first put a a resistor in series with the primary winding of the transformer, so that the voltage at the primary winding comes down to 220V again. I think you did this at another radio already. In the spoken text it was not explicitly mentioned that the Selenium rectifier was also changed, you only talk about changing the filter caps. At 5:20, the Selenium rectifier is still visible on the chassis, after the cut at 5:25 it seems that it was replaced with a Silicon rectifier. As the Si-rectifier causes a considerably smaller voltage drop than the Selenium type, an additional series resistor in this place may be still needed. Besides reducing the VB+ to the desired level, such a resistor has more beneficial effects by recreating the relatively high source resistance of a conventional circuit with a Selenium rectifier or even a rectifier tube. The angle of current flow is increased, distributing the delivery of charge into the filter caps over a longer period of time. So, at the same average current (which corresponds to the charge transferred), the peak current and consequently the RMS current are reduced, thus also reducing the stress on all parts in the rectifier circuit.

[@electronicsoldandnew]

You are absolutely correct. The drop in the primary voltage to 220V does in fact de-stress the transformer, and directly corrects the heater voltage. However, these old sets are quite hardy and generally don’t suffer much from the 5% over voltage. The same applies to the actual heaters, which, while reducing their life a little, can handle 6.6v quite comfortably. The idea of fitting the resistor into the B+ line is that it compensates for both problems - the mains over voltage and the smaller drop due to the silicon diodes. This option is not strictly correct, but generally most popular one implemented. In summary, as you said, two resistors should be used. Absolutely right. Thanks for your input.

[@alfredneumann4692]

This was the right entertainment for the sunday evening. As you measured the 270V, i saw, you have 3V ripple. Is this a problem?

[@electronicsoldandnew]

No, actually it's about the amount expected. In push-pull systems, the two tubes actually cancel out the hum on the B+ supply. That's one of the advantages of push-pull over single-ended. In SE systems you really need to drop that ripple a bit more.

[@someoneoutthere7512]

I've read alignment instructions in my native language, English, and I've been perplexed at times. As for a second language... forget it :)

[@electronicsoldandnew]

It’s sometimes not easy :)

[@danielsaturnino5715]

What do you mean electronics done? No Bluetooth reciever for mp3?

[@electronicsoldandnew]

I knew I'd forgotten something! Unbelievable! I will definitely fit one and report it. It'll be in the cabinet video. Thanks.

[@teslakovalaborator]

What's that silkscreen PCB in your leakage tester ? I guess a boost converter module, since you've installed a toroidal transformer in your switchbox which looked similar :D

[@electronicsoldandnew]

Really good eye! I’m experimenting with a cheap high voltage smps module to replace the transformer, which is quite pricey. If I like it (and so far it seems only “ok”) I might publish a “mod” for my tester project.

[@murat.eraydin]

how did you do "pan and zoom" at the begining of the video? what equipment do you use to shoot the videos?

[@electronicsoldandnew]

I simply use an iPhone camera. The pan and zoom is in the iMovie software that is use to edit the video. Very simple setup.

[@douro20]

At least you haven't come across a radio which has an ECLL800/6KH8 in it.

[@electronicsoldandnew]

No I haven’t. The ELL80 has shown its face a few times, but an “all in one” like that must be rare.

[@jonathanhendry9759]

Ah, so that's your accent. It was driving me crazy.

[@electronicsoldandnew]

Yes, PMB and Durban varsity. Then back to Madeira.

[@someoneoutthere7512]

I've seen so many mistakes in different schematics that if you see one it calls into question everything else.

[@mcimpoeru]

24:35 Von unten gesehen = view from below

[@electronicsoldandnew]

Thanks. I had to twist my head around to get the correct perspective :)

[@psionl0]

Considering how much voltage you had to drop after replacing the rectifier, it seems to me that an additional filter capacitor between the diodes and the resistor might reduce some of that voltage and reduce the amount of power that the resistor has to dissipate.

[@electronicsoldandnew]

That's a very good idea. I'll think about fitting a 22uF/450V cap there as I have a lot of them available. Thanks.

[@melissahermsen5630]

psionl0 If you put an additional filter cap directly after the silicon bridge rectifier you will cause a smaller angle of current flow and thus a higher peak current in the bridge rectifier and transformer secondary. For the same reason enlarging filter caps is not always a good idea! Use a scope with a current shunt to measure or do an LTspice simulation and view the repetitive peak charge current near the top of the sinewave and the angle of current flow from a sinewave source into a bridge rectifier plus smoothing cap with and without additional dropping resistor! The high internal impedance of selenium rectifiers did exactly what the external dropping resistor added to silicon rectifiers does; limit the repetitive(!) (re-)charging current near the peak of the sinewave And if a plastic cable tie is suitable as a permanent mechanical mount of these power resistors is questionable too.

[@_2N2222]

@@melissahermsen5630 This is an essential hint that goes along with my comment. In the datasheet of rectifier tubes you can sometimes see a maximum value for the filter capacitor specified. This is also with regards to the peak current.

[@jdmccorful]

Another carefully done job on this tunner. Enjoyed!

[@greengrayradio1394]

Very well done!

[@electronicsoldandnew]

Thanks