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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 18th Aug 2018, 2:54 am   #1
MurphyNut
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Default Long Wave interference problem solved.

Just following on from my previous thread about the bad interference I was receiving on valve radios, in fact so bad it was making Radio 4 almost inaudible.
I worked out the interference was coming though the mains and it was suggested trying a "mains conditioner" from a work college.
I found a review of this product (see link) and ordered one.

https://www.whathifi.com/tacima/cs947/review

I'm very impressed, though this product is aimed at Hi-Fi enthusiasts it really does an excellent job in almost removing all that back ground interference that was spoiling the enjoyment of my vintage radios.
It has to be pointed out most of my radios are down the end of the garden well away from the house where it works extremely well. For some reason It didn't perform anywhere as well when I tried the device in the house.
Hope this might be useful to someone.
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Old 18th Aug 2018, 3:58 am   #2
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Default Re: Long Wave interference problem solved.

It sounds as though your house wiring is pretty much alive with the interference. So when you operate a set there, the set is surrounded with it maybe as an electric field, maybe as a magnetic field. You're well within a wavelength of the radiating elements so a mature electromagnetic wave will not have formed so the field could be quite a lot stronger in one form than in the other. In the near field, the field strength of an unbalanced wave pair falls more rapidly with distance than you'd expect from the inverse square law applicable to balanced (377 volts per metre E-field for every ampere per metre of H field) mature electromagnetic waves. So the interference in the shed was mostly exported down the mains connection from the house. This would be why your new mains conditioner works better in the outbuilding than in the house. It shields your radio from mains-bourne interference, but not at all from radiated stuff.

Interference down the L and N wires of a mains connection either could be differential mode where L and N bounce around together, or it could be common mode where both bounce around together with respect to earth. And it could be a mixture of the two modes.

Your experiment with an X-class capacitor across L-N showed that the differential mode wasn't the worst culprit. That leaves the common mode as the offender.

Class-Y2 capacitors from L-E and N-E work on the common mode but can do a limited amount on their own. They also tend to simply couple the muck onto the earth wire as well.

Where Y capacitors come into their own is in conjunction with a common mode choke - the large wound toroid seen in the window of the new filtered socket strip. This choke has windings carrying both the L and N connections to the load. They are phased so that the load's normal operating currents creates opposing fields which cancel. This means that the power consumption of the stuff being powered doesn't act to saturate the core while the choke provides helpful impedance to interference driving L and N in parallel. Helpful enough to make the wanted improvement in this case.

I've sometimes seen large industrial filter units at radio rallies and you might find something adequately rated to handle the mains input to the outbuilding, or you could add one with mains wirie L and N wound together on a suitably large ferrite core. This would filter the supply to the whole outbuilding, not just the sockets on one strip. Or you could just get enough filtered strips to feed everything via one.

One disadvantage to having a lot of Y-mode capacitors is that their reactive current is sensed by RCDs. Have enough total microfarads and you start to get nuisance tripping. Of course, when an RCD trips your first thought is that there is a fault

The lab at work has just had to be re-wired with twice as many, smaller rings, each with a separate RCD, not because of the total power consumption, but because of the amount of L-E leakage in filter Y capacitors of a large number of pieces of low power gear.

David
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Old 18th Aug 2018, 6:38 am   #3
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Default Re: Long Wave interference problem solved.

Very informative and well explained....thank you!
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Old 18th Aug 2018, 1:26 pm   #4
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Default Re: Long Wave interference problem solved.

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Originally Posted by Radio Wrangler View Post
I've sometimes seen large industrial filter units at radio rallies and you might find something adequately rated to handle the mains input to the outbuilding, or you could add one with mains wirie L and N wound together on a suitably large ferrite core. This would filter the supply to the whole outbuilding, not just the sockets on one strip. Or you could just get enough filtered strips to feed everything via one.
David
Many thanks David for that in-depth post. Ultimately it would be much better to filter the mains supply before it gets to my outbuildings, I actually have 3, all containing valve radios I listen to regularly. The strip is great but a pain having to unplug and move it if I want to enjoy a particular radio in a diferent location.
Now I'm starting to understand whats going on I'll have to look into making some sort of permanent wound/ferrite filter.
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Old 18th Aug 2018, 3:10 pm   #5
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Default Re: Long Wave interference problem solved.

You might want to put a call out for scrap LOPT cores and any big ferrite cores going free

David

Of course, there are people on here who'd rebuild the whole telly from just one surplus core... So diplomacy may be needed.
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Old 19th Aug 2018, 9:58 am   #6
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Default Re: Long Wave interference problem solved.

A couple of homebrew designs here, which might be of interest - one more complex than the other:

http://www.dms-audio.com/sites/defau...ins-filter.pdf

http://www.decdun.me.uk/mainsconditioner.html
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Old 19th Aug 2018, 12:18 pm   #7
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Default Re: Long Wave interference problem solved.

Great thread, very useful to know. I will most probably being doing something similar myself. The problem with that commercial one is that it squeezes the soundstage somewhat and can impact on treble adversely How about that then? News to me that a mains filter can affect the audio output in that way! Never mind, I love What Hifi..
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Old 19th Aug 2018, 2:44 pm   #8
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Default Re: Long Wave interference problem solved.

The MOVs are a very good thing, they take the hit of voltage transients that would flash over he X capacitors across the mains. I've always joked that X capacitors are a form of dosimeter - by measuring how much capacitance they have left, you can assess how dirty your mains is as far as transients go.

Those filters look quite good. Such things also work both ways, they will keep the noise from noisy gear from getting onto your general supply. Once this was important, but it's a bit of a lost cause nowadays. Still it's a good idea not to have anything noisy on the downstream side of the filter along with what you're trying to protect.

It's always the soundstaging which goes first, however if you switch over to the right sort of electricity, it can be made a lot better. Go for wind and hydro power. The much larger total rotating masses (and the moving water mass) make them much stiffer supplies than gas and steam turbines, consequently the supply is less effected by the demands of audiophile amplifiers. A simple change of contract and you'll be able to post about an awesome improvement. The only drawback is that you'll be forced to listen to all your records again. 'Irreproduction" the journal of high-end subjective superiority said it was at least twice as good as running an especially expensive green pen round the edges of all your LPs.

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Old 21st Aug 2018, 2:52 am   #9
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Default Re: Long Wave interference problem solved.

Quote:
Originally Posted by stevehertz View Post
The problem with that commercial one is that it squeezes the soundstage somewhat and can impact on treble adversely How about that then? News to me that a mains filter can affect the audio output in that way! Never mind, I love What Hifi..
I've always felt there's so much daft stuff written connected with Hi-Fi, and that What Hi-Fi review is a prime example.
Thought I'm glad it didn't put me off purchasing the item, it works remarkably well with old radios, money well spent!
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Old 21st Aug 2018, 7:23 am   #10
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Default Re: Long Wave interference problem solved.

The window over the filter components may seem twee but it is a good thing.

There is an issue with a lot of PC power supplies where their printed circuit board is laid out to take the components for a decent mains filter to stop outgoing muck, but the components aren't loaded. Shunt capacitors are simply missing and wire links are loaded in place of much more expensive chokes.

It's suspected that fully loaded filters are provided in units going for approvals testing, and once they have the paperwork signed, the production units are cheapened-off and dirty.

There seems to be no downstream enforcement of standards.

So, seeing the parts in position is reassuring that you're not being taken for a ta-ta.

David
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Old 21st Aug 2018, 12:48 pm   #11
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Default Re: Long Wave interference problem solved.

It also reassures that there are no RIFA smoke-bombs lurking within.... It looks to be pretty comprehensive, with a GDT included (gas discharge tube, the small round white wire-ended thingy), a tough beastie that helps quench switching and lightning spikes- as long as the lightning isn't too close or severe, there's always a point with lightning where all bets are off! Also the (Y?) ceramic capacitors look to have a thermal fuse sandwiched to them with heat-shrink, cutting them out of circuit if they overheat with really noisy mains. (The top, lone blue disc might always be a MOV rather than a ceramic capacitor, again not a bad idea to thermally fuse one of these, they can get to a point where they weld through under severe overload.)
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Old 21st Aug 2018, 10:38 pm   #12
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Default Re: Long Wave interference problem solved.

I came unstuck once demonstrating a newly repaired set to the owner who had come to collect it. Placed nicely on the antique table in the hall, all wavebands were filled with horrible interference on all AM wavebands. Red faces, until I realised the circulating pump for the fish tank through the wall in the next room, at just the level of the set, was causing the interference..
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Old 24th Aug 2018, 2:05 pm   #13
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Default Re: Long Wave interference problem solved.

Quote:
Originally Posted by David G4EBT View Post
A couple of homebrew designs here, which might be of interest - one more complex than the other:

http://www.dms-audio.com/sites/defau...ins-filter.pdf

http://www.decdun.me.uk/mainsconditioner.html
Hi David

Thanks for the links for the mains conditioner projects. When I can find the time, I'd like to build the ETI circuit as per your second link which looks a very comprehensive conditioner.
When I contemplate building such a project, which usually takes me many months to get aroud to, I always like to find the difficult parts in advance. In this case the the Ferroxcube toroid and the varistors or VDRs. I noticed CPC stock a couple of likely substitutes for the varistors, https://cpc.farnell.com/epcos/b72207...75?st=Varistor and https://cpc.farnell.com/epcos/b72210...86?st=Varistor and wondered if these would be suitable? Maybe use 3 of each rather than 6 of one type?

Regarding the FX 4054 Ferroxcube toroids, I checked in my 1988 Mullard Quick Reference Guide and it describes this nylon coated toroid as grade 3E2 (blue), dimensions 23 x 14 x 7mm. Finding a suitable alternative is proving a little difficult though it's probably not that critical. Any suggestions for a suitable toroid for this project?

Regards
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