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Old 31st Oct 2011, 3:01 pm   #1
davidhood999
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Default Adding earth lead to vintage radio.

Hello, I am looking at buying a 1950s/60s Roberts Radio, but I note that it only has a two line wire (excuse the terminology) as opposed to modern day 3 line wires. Is it easy to add a modern wire to these old radios? As I would be adding the earth (I think!) lead, where is a safe place to attach it to? This would be the first time that I dabble in this sort of thing, so please tell me if you all think I might be biting off more than I could chew. Cheers!!
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Old 31st Oct 2011, 5:18 pm   #2
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Default Re: adding earth lead to vintage radio

Can you please post the model number, so that the service info can be looked up?

Thanks
Dave
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Old 31st Oct 2011, 8:21 pm   #3
G8HQP Dave
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Default Re: adding earth lead to vintage radio

If the set has AC/DC arrangements then adding an earth connection is not possible.
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Old 31st Oct 2011, 8:38 pm   #4
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Default Re: adding earth lead to vintage radio

I'd be very interested as well on how to add an earth lead. I recently carried out my first restoration on a Bush AC11 set, and wonder if there are any major safety implications in the set not being designed with one.

Ian.
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Old 31st Oct 2011, 9:38 pm   #5
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Default Re: adding earth lead to vintage radio

Hmmm - three Daves in this thread already, eh?

David (original poster) - I know little about this subject, but I'd go with what G8HQP Dave says. Though, as per davidgem, if you can post the model number, you might get an unconditional yes/no response!

Ian (Orthicon) - you may find something useful in these threads:

https://www.vintage-radio.net/forum/...ad.php?t=67587

https://www.vintage-radio.net/forum/...ad.php?t=47092

where the topic of earthing has been discussed. I think I've seen other threads on this topic as well, which you may be able to discover using the 'search' button in the blue bar above.
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Old 31st Oct 2011, 10:14 pm   #6
ian rose
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Default Re: adding earth lead to vintage radio

Hello

My understanding is that it is unwise [possibly hazardous] to add an earth connection to an AC/DC set. The chassis may well be on the live side or neutral side of power input.
In certain designs including AC/DC communications receivers the chassis may be isolated from either side of the power input in which case it is safe and may, indeed, be desirable, from reception point of view, to connect an earth to the designated terminal or socket.
Adding an earth connection to a model designed for AC mains only [where there is a mains transformer providing isolation from the national grid] it is safe and could again be desirable from a reception point of view to connect an earth to chassis.
Such a connection need not be via the mains lead but via an extra conductor to an earth spike into the soil or to a water pipe [not plastic or alkathene].
Most AC only sets provide an earth terminal or wander plug socket which effectively earths the chassis when connected.
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Old 31st Oct 2011, 11:42 pm   #7
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Default Re: adding earth lead to vintage radio

So in an AC only set like my AC11 if using the earth mains lead in a three core flex to earth the set-

This would involve soldering the earth mains lead from the flex onto the earth wander plug connection from inside the chassis - as I understand.

Would there be any benefit in connecting a Y2 class capacitor between the connection, and if so what value should be used?

Ian
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Old 31st Oct 2011, 11:53 pm   #8
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Default Re: adding earth lead to vintage radio

In those circumstances, adding the Y2 capacitor would nullify any safety advantage from earthing the chassis, though it would leave any RF improvement intact. The point of a safety earth to the chassis is simply to prevent the chassis from becoming live in the event of an insulation failure in the mains transformer (or possibly a stray broken off live wire coming into contact with the chassis). It does this effectively (historically) by blowing the supply fuse in the event of such a failure or more likely nowadays by tripping any RCD in the supply.
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Old 1st Nov 2011, 12:19 am   #9
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Default Re: adding earth lead to vintage radio

It's not wise to guess at or generalise about this topic, as it is a matter of electrical safety. For any given set, there will be a correct answer as to whether is it possible to add a safety earth (as distinct from an RF one). There will also be a less clearcut assessment on how much of a safety improvement will be achieved by adding one, depending on the effectiveness of the particular model's original insulation. If it is indeed possible to earth the chassis, then for optimum safety a secure connection from the mains plug to the metalwork is what you want, not via the original wander socket wiring and not to a rod in the ground.

As Herald says, if you always run the set via an RCD, some would argue that it is almost impossible to get a fatal shock from it anyway, no matter how poor its intrinsic safety arrangements are. FWIW I never do this kind of modification, I control the risks by careful usage and monitoring, proceeding as though there were no RCD to protect me, but using one anyway. For general family usage, adding an earth where possible would perhaps be more beneficial.

Lucien
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Old 1st Nov 2011, 1:24 pm   #10
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Default Re: adding earth lead to vintage radio

Adding an external earth (e.g. to a rod in the ground) should only be done by people who really know what they are doing, as it can reduce safety in some cases. This is because 'ground' (i.e. incoming mains third conductor) is not necessarily at the same potential as your garden. Provided everything metal in your house is bonded to the same 'ground' than all is OK, but introducing a different 'ground' can mean that two different pieces of metal in the same room are at significantly different potentials which is precisely what earth bonding is supposed to eliminate.
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Old 5th Nov 2011, 6:13 pm   #11
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Default Re: adding earth lead to vintage radio

Quote:
Originally Posted by davidgem1406 View Post
Can you please post the model number, so that the service info can be looked up?

Thanks
Dave
The radio is a Phillips R66 from 1956


Thanks for all the other posts, I am a bit baffled by the terminologies used by some people though. Lay man's terms is good enough for me

I see that the answer to my question is no with some radios but not others. How can I tell by looking at the radio, or if in this case it's on Ebay and I cannot physically see it, what questions should I ask the seller? Is it indeed safe to use a model that you cannot add earth wires to and have to use traditional 2 strand wire?

Thanks again.

David Hood.
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Old 5th Nov 2011, 6:28 pm   #12
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Default Re: Adding earth lead to vintage radio.

I assume you mean "Philips" rather than "Phillips"? Either way I can't find any service data for an R66.

Do you mean Roberts R66?
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Old 5th Nov 2011, 6:28 pm   #13
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Default Re: Adding earth lead to vintage radio.

The chances are that the Ebay seller won't know either!!

If there is a transformer inside the set, then it would be OK to earth it in most cases. If it has a dropper resistor, then don't.

Look at the valve types - If they are U series then it's AC/DC and I wouldn't earth it. If it's 'E' series then you should be OK. For other valve types, there is usually an equivalent 'E' or 'U' number.

If you're not sure, then please ask. We would all rather you did rather than take any risks.

With AC/DC sets, make sure that the chassis is connected to Neutral and NOT live. They are safe then.

Cheers,

Steve P.
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Old 5th Nov 2011, 6:34 pm   #14
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Default Re: Adding earth lead to vintage radio.

I wonder if you mean Roberts R66?

A photo would help! But if it is, then you can earth it if you want but in this case there isn't much point.

Cheers,

Steve P.
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Old 5th Nov 2011, 6:42 pm   #15
Lucien Nunes
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Default Re: adding earth lead to vintage radio

Quote:
Is it indeed safe to use a model that you cannot add earth wires to
There's a whole spectrum covering all aspects of safety, not just electric shock risk. After all, what's the use of earthing a radio chassis if it later catches fire and burns the house down. In general terms, a chassis that can be earthed will normally be safer once it is earthed, although with well-constructed sets the difference is not a great one unless something else is amiss.

If I were leaving a radio in the house for daily use by anyone in the family including children, who might not spot trouble as readily as experienced users, I would reckon it worthwhile to add an earth where possible unless the integrity of the insulation afforded by the case is really excellent. I would certainly power it via an RCD, and possibly strap a thermal fuse to the mains transformer. For my own purposes only, the RCD is enough.

It is important to distinguish between transformerless (AC/DC or universal) sets and ones with a mains transformer. Transformerless designs are much more likely to present a shock risk, although this can sometimes be mitigated by ensuring the mains lead is connected with the correct polarity. In general they cannot be earthed, so you are stuck with the residual risk, albeit a low one if you have RCD protection on your electrical supply. Any set with a mains transformer is likely to be safer than a universal, regardless of whether it has a 2-core or 3-core mains lead. These are often described as AC-only sets in contrast to AC/DC.

For comparison it's worth noting that well into the 1980s many TVs had 'live' chassis just like 1940s universal radios. Worse, in some respects, because the chassis couldn't be connected to the neutral side of the supply let alone earthed, due to being connected after the rectifier. They would have been built using more modern insulation techniques but the principles are the same, yet we wouldn't consider these especially dangerous today.

You will rarely get a useful answer on these points from a non-technical seller, as they won't understand the electrical theory that governs the safety aspects of receiver design. You can always ask here if you have the model number or look up the set's specification online, and please don't be afraid to ask for clarification of unfamiliar terms.

Lucien

E2A Steve's post beat me to it covering some of these points already!
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Last edited by Lucien Nunes; 5th Nov 2011 at 6:50 pm. Reason: Additions
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Old 5th Nov 2011, 8:08 pm   #16
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Default Re: Adding earth lead to vintage radio.

Hi David (OP),

Steve's already mentioned making sure that the chassis is connected to neutral, but to make this explicit, that means the BLUE lead. The brown lead is live. Sorry if you already knew this, but if you get this wrong, and, say, touch a grub screw when you're tuning the set or changing the volume or tone, you could be fatally shocked. It's that easy.

Lucien talks about the merit of using RCDs with this sort of set. Just to add that (I think) he means an additional one at the socket, not just the big fat ones on the distribution board under the stairs. I have one for each opearational vintage apparatus.

What is/ was your main rationale for wanting an earth, as a matter of interest?
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Old 5th Nov 2011, 8:26 pm   #17
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Default Re: Adding earth lead to vintage radio.

HI David

To be honest , I dont think anybody on here can give you a definite answer on here from the information that you have supplied , and it is alway arguable whether you should attempt to modify vintage radios anyway , all my collection of radios and televisions are original and most are fitted with 5 amp , two pin plugs ,
However I would never leave any of them connected when I was not in the room and I would be very careful not to allow children or uninformed people to tinker with them .

What would be of more help to you is to obtain the said radio and then ask one of the local members of the forum if you could bring the radio over for them to take a look at and then they could give you a definate oppinion on the mains arrangements .
Also , you would probally learn more in an hour looking over somebody's shoulder that just looking at the PC ( I did ) and without going off topic too much , I can really thank one respected member of this forum for giving me vast amounts of help and teaching me vast amounts about restoring vintage televisions .

Good Luck

Peter

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Old 5th Nov 2011, 9:04 pm   #18
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Default Re: Adding earth lead to vintage radio.

Quote:
Originally Posted by davidhood999 View Post
I note that it only has a two line wire (excuse the terminology) as opposed to modern day 3 line wires.
A lot of modern equipment is actually not earthed (although admittedly better insulated). With English plugs it may not be so obvious (although if the earth pin is a lump of plastic rather than copper that's a good indication) but with German plugs it's quite obvious if the earth connectors are missing. Don't forget that the set was designed for daily use and was considered safe enough at the time.

If the set has no transformer, I suggest running it via an isolating transformer if you want to be really safe. If you intend to take up collecting radios seriously, that would be a good investment in any case.
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Old 5th Nov 2011, 9:06 pm   #19
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Default Re: Adding earth lead to vintage radio.

Quote:
I think he means an additional one at the socket
It doesn't matter where the RCD is, provided it is of the normal type used to protect against electric shock, and it works. All new domestic ring main circuits are required to have them in the distribution board, many existing installations have them too. Before relying on an older RCD in the distribution board, check that it states IΔN 30mA, (read I-Delta-N) meaning the sensitivity is such that if 30mA leaks from the circuit then the breaker will trip. Test it regularly by pressing the test button which should cause it to trip immediately.

If you are connecting your set to a socket outlet that isn't RCD protected at the distribution board, then a plug-in type such as recommended for garden equipment is equally suitable. Use both, if you like, there's no harm in doing so.

An RCD is not a substitute for earthing, however it achieves one of the same aims (to lower the risk from electric shock) by a different method. It will protect a transformerless (AC/DC universal) set just as well as an AC-only set, which earthing cannot do.

Lucien
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Old 5th Nov 2011, 9:22 pm   #20
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Default Re: Adding earth lead to vintage radio.

I'm afraid the statement that "AC only set chassis can be earthed, AC/DC set chassis can't" is a bit simplistic. There are sets such as the Kolster Brandes toaster radio KB10 which have a heater transformer and "E" range valves and are AC only, but are still live chassis.

Your best option is to check the service manual (or get others here to do it for you) and/or measure the resistance between the chassis and both sides of the mains. If the chassis is isolated from the mains, then adding an earth connection with a 3-core mains cable can add safety if an insulation fault occurs.

If the chassis is not isolated from the mains, then you need to rely on very old insulation for safety. Making sure the chassis is connected to mains neutral not mains live and adding an RCD, either in the house consumer unit or in the radio mains plug, is a good idea.

Stuart
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