Classic cars forum & vehicle restoration.

[FAB Cruiser]

I’d appreciate some advice on suppression for my 1957 Ford Zephyr (Straight six, converted to negative earth with alternator). I’m getting a small amount of interference with the CD radio and also getting problems with my alarm (details in a separate thread).

I’ve seen a set of original KLG suppressed spark plug caps on ebay. They are the screw in lead type, which are at a right angle compared with the standard caps. Would these help and how do I replace the originals?

Any other suggestions on suppression appreciated.

Thanks
David

[peter scott]

What does the interference sound like on the radio? Is it a tick tick tick at tick over or is it more of a whine?

Peter

[FAB Cruiser]

Hi Peter,

It's more of a whine. It's hardly noticeable on CD, a bit worse on FM and terrible on AM.

I just installed an inline filter for the Radio/CD (£8 from Halfords). It filters the earth and the 'accessory live' (but not the permanent 12V). And guess what. yep, it amplifies the interference and makes it worse! I'll take it back tomorrow!

Cheers
David

[47p2]

Sometimes you can suppress everything and still get interference breaking through. It might be worth having filters fitted inside the radio
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ROVER
One of Britain's Fine Cars

[peter scott]

Hi David,

It sounds like the noise is coming from your alternator. As a check try running the engine without the fan belt. If this stops the noise then I think
you should exchange your filter for one of these @£3.99:

http://www.halfords.com/webapp/wcs/stores/servlet/SearchCmd?text=suppressor&action=search&storeId=10001&catalogId=10151&langId=-1&x=195&y=104#

It should be mounted on the alternator.

HTH

Peter

[Uncle Joe]

I would think that Peters advice is spot on. When you fit the suppressor, pay attention to the earths as well, including the aerial.

Is it an alternator or dynamo that you have? Not that it makes much difference!

[FAB Cruiser]

It's an alternator.

You're advice makes sense because the original valve radio has AM which although I've never used it (+VE earth) it presumably would have been interference free as a factory accessory.

I'll take back the inline radio "filter" and swap it for the alternator one and let you know how it goes.

I'd rather do that before I try plug caps as I'm concerned they'd affect the cars performance.

Cheers
David

[FAB Cruiser]

Latest update, the problem isn't the alternator.

Halfords didn't have the filter capacitor in stock, so as a test I removed the fan belt.

Without an alternator running the interference on AM died a bit, but I still have serious interference effecting my alarm. Details of that problem are on another thread in this section if you have any suggestions.

Thanks
David

[Uncle Joe]

I di point this out earlier, but you have made no reference to doing it. Check the earths, every single one of them. Over the whole car!

[ukdave2002]

Hi FAB Cruiser
The alarm is probably suffering from electrical noise the main power to it. I would fit a Contact Suppressor, you won’t find these in motor factors, but they are commonly used in the electronics industry to suppress electrical noise.

The common name is a “snubber” you fit them straight across the power/battery supply to the individual components. Ideally you fit these at the source of the interference , but as this can be a pain to pinpoint fit them on the devices being affected, so I would fit one on your alarm and one on the radio, they are not polarised so can be fitted either way round and only cost a couple of quid.

The radio interference as others have commented does sound like the alternator and you should still fit the suppressor on the alternator as Peter recommended, and as UJ commented make sure the earths are good.


http://www.maplin.co.uk/Module.aspx?ModuleNo=498&doy=31m8&criteria=Suppression

[FAB Cruiser]

Yes I've been checking all the earths as recommended and am looking for the alternator capacitor. All the local Halfords are our of stock.

The snubber looks like a great idea.

Should I use one in both positive feeds (Permananet 12V and Ingition switched 12V). Both the alarm and radio require these two feeds.

Also should I use one on the positive feed between alarm control unit and siren?

Do they go in-line on the positive supply or do they sit across positive and earth?

Thanks
David

[pigtin]

While on the subject of supression: I can't get my rev counter to indicate correctly. It seems to reach 5k and settle a little but swings about at lower rev's. It's fitted to my special and I don't know what it was originally from.
There are 3 connections: 0. and +12 and one to the distributor. I wondered if I may need to iron out the spikes a little with a supression capacitor? or perhaps it's just U/S
_________________
Due to the onset of my mid eighties I'm no longer sprightly and rarely seen in my Austin special. I have written a book though. https://amzn.eu/d/7rwRRqL

[peter scott]

Hi Don,

When you say it reaches 5k then settles, is this just an initial kick when you turn on the ignition or are you saying it generally follows engine revs but is erratic at low revs?

If there was a problem with noise on its +12v connection then I think you would probably still see evidence of it even with the CB connection disconnected.
I guess you could put another capacitor between the CB connection on the back of the rev counter and the metal case. Likewise a second cap case to to +12v isn't going to do any harm.

Peter
_________________
http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

[pigtin]

Yes Peter, it is erratic at low revs, but on reaching 5k it doesn't seem to follow the engine revs... pretty useless actually, I was just hoping it might just be a suppression problem. Will try what you suggest... thanks.

Don.
_________________
Due to the onset of my mid eighties I'm no longer sprightly and rarely seen in my Austin special. I have written a book though. https://amzn.eu/d/7rwRRqL

[peter scott]

Hi Don,

Actually, from what you say, I wouldn't be surprised if a capacitor added
to the CB connection made the rev counter top out at a lower rev figure.

Is your rev counter one of the current sensing types that has the contact breaker to coil connection looped, with a few turns, through the rev counter?
The chances are that your problem is due to the amount of ringing on the pulse stream and if you could adjust the threshold that the rev counter uses to sample the pulses then you might get rid of the erratic behaviour. I'm just guessing but perhaps the rounding off at 5k is due to the pulses reducing in amplitude. Whatever, being able to fiddle with the decision threshold could be the answer.

I have a very distant memory of opening up one of these electronic rev counters and it having two adjustment pots. One for the threshold and one to calibrate the meter. You could go in there and have a fiddle. The problem will be that they are probably not marked so you won't know which is which. However you can get around this by carefully marking their positions prior to fiddling, so that you can always restore it to the starting point if the worst comes to the worst.

If you don't fancy messing inside then if you have the type that has a few turns of the wire from coil CB to distributor CB then you can try adding or removing a turn or two.

Peter
_________________
http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon