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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 5th Nov 2011, 9:31 pm   #21
Dave Moll
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Default Re: Adding earth lead to vintage radio.

Quote:
Originally Posted by Lucien Nunes View Post
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.
When using both RCD's, it may be worth ensuring that the plug-in one has a lower IΔN rating if possible - otherwise it could be random which one (or both) will trip.
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Old 5th Nov 2011, 9:39 pm   #22
davidw
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Default Re: Adding earth lead to vintage radio.

Is it one of these by any chance? http://www.radiomuseum.org/r/roberts_r66r_6.html
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Old 8th Nov 2011, 9:34 am   #23
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Default Re: Adding earth lead to vintage radio.

In a perverse sort of way, AC/DC receivers might be easier to deal with than the AC type from the valve era.

If an AC/DC receiver is provided with an “earth” socket, then it will be for AM aerial RF purposes only, and will likely be connected to the chassis by a suitable isolating capacitor. (Or perhaps there will be an isolated aerial input coil, although I think that approach was less usual.) Thus the earth socket may be connected to whatever is the most suitable and lowest RF noise earth in order to complete the circuit of a long-wire type aerial. This is unlikely to be the earth wire of the mains wiring, although perhaps a separate and independent connection to the main house “earth source” would be acceptable. Because of the potential live chassis nature of AC/DC receivers, one assumes that their manufacturers took reasonable precautions to make them adequately safe in operation (by the standards of the day) even though they could not have any kind of safety earth connection.

In AC receivers fitted with isolating-type mains transformers and two-core mains connections, the earth socket (connected to chassis) typically serves as both safety earth and RF earth, and therein seems to lie the problem. Since such chassis are unlikely to be double insulated, they should be operated with a safety earth, and this should be via the mains earth only. But as this is unlikely to be the lowest noise RF earth, then there is the temptation to use an arrangement that is better from an RF viewpoint, but not from a safety viewpoint, such as a separate connection to the house “earth source” or I think even worse, a connection to a separate earth altogether. I suspect that operating instructions did not always make it clear to non-technical users that there were two issues involved, earthing for safety and earthing for best reception.

Given that safety should take precedence, then the RF side would have to get by with second-best when it comes to earthing. But there are ways out. If the receiver is operated with an AM aerial, such as a loop, that does not depend upon a return earth path to complete its circuit, then the lack of an optimum RF earth path is of lesser concern. The same would apply to the old antistatic aerial systems wherein the RF earth required to complete the circuit from the upper transformer primary could be independent of any earthing arrangements of the set itself. (The more recent so-called longwire balun systems strike me as a somewhat crude reincarnation of the antistatic system that was by all accounts very well developed by the major UK manufacturers, although Wellbrook seems to have done more than most to recover the original precepts, and does offer an aerial isolating transformer as part of its range.)

FM-AM receivers might have presented an additional problem when fitted with an unbalanced coaxial FM aerial input whose earthy side was connected to chassis. Perhaps not in the UK, but in other places such as the US it is usual to route a coaxial feeder from an outdoor aerial via an earthing block that is connected to the house earth source. If the receiver was also earthed via its earth socket, then there would be a double earth connection, which is undesirable. Braid-breaker type aerial transformers would solve this problem. I also found that back-to-back 75-to-300 ohm baluns worked insofar as they stopped any hum loops from this source, although whether they were appropriate from a safety viewpoint I don’t know, but suspect not.

I suppose the best approach in any situation is to work out what is needed from a safety viewpoint, and then arrange any RF earths in a way that does not compromise safety.

It gets even more complex when one considers valve-era hi-fi components which could be operated on a mix-and-match basis. Certainly hum loops and safety could come into conflict, and as well as the RF and safety aspects, earthing arrangements for turntables and tone arms need to be arranged to minimize hum transfer.

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Old 8th Nov 2011, 2:12 pm   #24
davidhood999
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Default Re: Adding earth lead to vintage radio.

Hello all.

Thanks again for all the info given. The Radio in question has sold now, so maybe I will look for another..... and YES it was a Roberts R66 and not a Philips as I incorrectly stated. When I find another that I like and I get it at a price I an happy with, I will be back here to ask you all once again what you think I should do with it.

Many thanks.

David Hood.
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