Earth fault

[bernardgreen]

There are two basic reasons and next is to find out which it is.
1) There is something wrong with house earth.
2) The radio has some inductive or capacitive link and needs an isolation transformer.

Add the third reason ( which is related to [1] )

[3] the neutral in the local supply network is far from true ground potential.

I seem to recall that many of the hilltop sites I visited had used only local true grounds for earthing.

"hilltop sites" is a historic description of locations of transmitting and receiving equipment. They are now not always located on hilltops but can be on buildings but still require special arrangements for earthing dueto the conflicts between safety "earths" and equipment earthing.

 

[Paul_C]

As to the voltage the Avo Mk8 being an old analogue meter I think from memory 20,000 ohms per volt presents the circuit with a resistance. Without pulling mine from it's resting place can't remember the scales but seem to remember something like 30, 100, 300 volt. Think the Mk7 was 50, 100, 500 volt but long time ago.

Don't confuse the Avo model numbers with the different marks of each model.

The original Avo 8 was 20,000 ohms per volt on d.c., but 1000 o.p.v. on a.c. on the 100V range and above. The basic a.c. sensitivity was increased to 2000 o.p.v. from the Mk. IV. The voltage range sequence was originally 10-25-100, but this was changed to 10-30-100 from the Mk. V onward (with the extra 500V d.c. range becoming 600V).

The Avo model 7 was the older design dating back to the 1930's, with a basic sensitivity of 500 o.p.v. on both a.c. and d.c. ranges. The range sequence was 1-10-100 but with the addition of a 400V range, and it also had the divide-by-2 button which halved the f.s.d. of each range and doubled the sensitivity to 1000 o.p.v. when pressed.

 

[evanrob]

Hello again automationman, first of all my apologies for stating the 'isolated 'earthing rod , should have know better, also , the RCD yes I do appreciate that this has no bearing on my particular 'problem'..and does not come into the picture. Incidentally there is one of those miniature fenced off 'substations' approximately 30 metres from my house !! ???
You asked. if connecting the 'live ' earth wire to the radio chassis made any difference. well, in a word, regarding mains borne noise ,, NO... What did happen , as I half expectrd, was a variation in the aerial current reading. ,standing wave ratio (SWR) which a small tuning adjustment ,corrected .
As for Bernard's suggestion re the lamp shunt , yes ; the voltage read zero..
All in all, gents , perhaps I have 'made a mountain out of a molehill' for which I apologise.. As I mentioned earlier,.. Paul C, AC/DC and of course live chassis were more or less the norm, before that of course, were the old (wonder if you remember them??) battery radio (wireless) sets Cossor, Lissen Burndept,Ecko; powered by the old so-called 'Accumulators' and 'eliminators' , ?? etc etc ---( nostalgia is taking me away from the subject....) Age does that I suppose ?
However, gentlemen; I let the matter rest there ,and may I say , many many thanks for your interest and interesting comments and help in enlightment, so very much appreciated, and I shall continue to watch and hopefully, still learn, via these forums God Bless

 

[bernardgreen]

All in all, gents , perhaps I have 'made a mountain out of a molehill' for which I apologise..

Better to ask and be certain and as a result not risk breaking an ankle in tunnel under a innocent looking mole hill.

And the nostalgic memories invoked were good.

 

[automationman]

Glad you asked the questions, they led to an interesting and nostalgic conversation.

I do miss the mercury arc rectifier though, saw my first one during an open day at Plymouth Dockyard in 1963 and thats what "sparked" my interest in all things electrical.. the days when you could actually see electricity

 

[Paul_C]

before that of course, were the old (wonder if you remember them??) battery radio (wireless) sets Cossor, Lissen Burndept,Ecko; powered by the old so-called 'Accumulators' and 'eliminators' , ??

A little before my time to remember them when then were in their heyday, but as an enthusiast of old radio equipment I'm certainly familiar with them. And while on that nostalgia trip, don't forget the battery portables which were common in the 1940's/50's before transistors took over. I still have a couple of those stashed away somewhere, although finding the 90V H.T. batteries is a little harder now.

 

[bernardgreen]

Please stop it

I am becoming very nostalgic for the good old days.