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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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6th Aug 2020, 4:26 pm | #1 |
Octode
Join Date: Sep 2009
Location: Bath, Somerset, UK.
Posts: 1,033
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Zenith Trans Oceanic H500. Mains potential at Volume Control
I've just popped this poor radio out of its case to see if the repairs to the rexine are within my capabilities (they are not!).
I tried the radio while out in the garden and using an external mains socket. It worked fine so I went to turn it off and got a tingle! Upon measuring from the metal stem of the volume/on/off switch to ground it showed 247v on the AC scale of my DVM. I'm guessing it is a live chassis - but is it wired up backwards? Surely the metal volume pot shouldn't be + mains? When I say ground, I mean the black lead stick into the gaps in the paving slabs. SEAN
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6th Aug 2020, 4:38 pm | #2 |
Octode
Join Date: May 2009
Location: Stevenage, Herts. UK.
Posts: 1,515
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Re: Zenith Trans Oceanic H500. Mains potential at Volume Control
Yes, it's live chassis! The original US mains plug on the vacuum cleaner style sprung reel was reversible...
What plug is fitted to yours, has a previous owner wired a UK plug backwards? Another good safety feature was that the 90v HT battery connector is male, the female is on the radio end - what were they thinking? |
6th Aug 2020, 5:51 pm | #3 |
Octode
Join Date: Sep 2009
Location: Bath, Somerset, UK.
Posts: 1,033
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Re: Zenith Trans Oceanic H500. Mains potential at Volume Control
It has a UK plug on it.
I'll swap it around and check again (with a meter!!!) Cheers SEAN
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There are only 10 types of people, those who understand the binary system, and those who don't. |
6th Aug 2020, 6:29 pm | #4 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Zenith Trans Oceanic H500. Mains potential at Volume Control
According to a schematic I'm looking at, one side of the mains isn't connected directly to the chassis it's connected to the chassis via a 0.047uF and a 330k in parallel, on mains HT-ve isn't chassis.
On battery HT-ve is chassis, so far as I can make out. Lawrence. |
7th Aug 2020, 7:18 am | #5 |
Octode
Join Date: Sep 2009
Location: Bath, Somerset, UK.
Posts: 1,033
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Re: Zenith Trans Oceanic H500. Mains potential at Volume Control
Odd, I tried it in the house on a known good ring main - same result.
I've swapped the plug around - checked and it is now less lethal! SEAN
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There are only 10 types of people, those who understand the binary system, and those who don't. |
7th Aug 2020, 7:51 am | #6 |
Octode
Join Date: May 2009
Location: Stevenage, Herts. UK.
Posts: 1,515
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Re: Zenith Trans Oceanic H500. Mains potential at Volume Control
Lawrence is quite right, the chassis connection is not direct. It's a while since I've been inside mine, but obviously it's still safer if the CR go to neutral rather than live. Mine still has a US plug, but I've marked it so I know the right way round when plugged into a standard shaver adapter.
On my T-600 you have to have a US mains plug or you can't switch to battery operation. |
7th Aug 2020, 8:29 am | #7 |
Octode
Join Date: Sep 2009
Location: Bath, Somerset, UK.
Posts: 1,033
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Re: Zenith Trans Oceanic H500. Mains potential at Volume Control
So although not direct, you would expect 243v? That is what I measured. I took a photo and one of it in the kitchen. I didn't want to be the earth, so I stuck the black probe into the first thing I had to had, a lettuce. I got only 23v with a poor earth!
SEAN
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There are only 10 types of people, those who understand the binary system, and those who don't. |
7th Aug 2020, 8:47 am | #8 |
Octode
Join Date: May 2009
Location: Stevenage, Herts. UK.
Posts: 1,515
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Re: Zenith Trans Oceanic H500. Mains potential at Volume Control
Yes, the 330k // 47n will certainly give you a tingle and if you measured the voltage with a DMM with high input impedance you'd see virtually the full 240v. The capacitor reactance is only 67.7k @ 50Hz and that's before considering any leakage it may have developed over the years.
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8th Aug 2020, 5:43 pm | #9 | |
Heptode
Join Date: Mar 2017
Location: Cedar Grove, Wisconsin, USA.
Posts: 823
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Re: Zenith Trans Oceanic H500. Mains potential at Volume Control
Quote:
First thing I would do is replace the 47NF with a 1000 or 1600 volt modern cap. We don't have that problem, as we only use 120 volt mains. BTW, the Tolex outer covering is usually in rough shape due to carless handling and usually treated as luggage. Even here, it's hard to find a real well cared for example. Dave, USradcoll1. |
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