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Author Topic: A decent, inexpensive DMM  (Read 4343 times)
WA2ISE
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Posts: 879




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« Reply #15 on: August 01, 2016, 08:32:31 PM »

... getting across the line at an electrical service panel with a cheap meter with the test leads in the current position will likely turn the meter into a grenade. 
...  much more on a commercial or industrial site.

I've heard stories of electricians getting killed by a good quality DMM when they tried to measure the voltage on what turned out to be 13.8KV lines.  DMMs usually safely top out around 1KV.  A ham troubleshooting his vacuum tube linear amp could get into trouble...
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K8AXW
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« Reply #16 on: August 01, 2016, 10:06:29 PM »

This is why I pointed out not using a cheap meter on HV HIGH ENERGY sources.  We had an electronic engineer put his Simpson 260 probes across a 2600V source.....once. He wasn't much good after that and they finally let him go.
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G3RZP
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« Reply #17 on: August 02, 2016, 08:20:21 AM »

I bought me a x100 probe, rated to 40kV for HV work.......about $30 new. Don't use it often but when its needed.....

When using it, I have the DMM on an insulated board  and despite the probe having safety flanges to allow it to be handled for 'dabbing onto' HV points, I don't!

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K8AXW
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« Reply #18 on: August 02, 2016, 09:28:59 AM »

Peter:  I was fortunate to pick up two HV probes at hamfests  (a couple years apart) each for a song and dance.  (I find that "singing and dancing" is easier than parting with money!   Roll Eyes  ) I follow the same procedure as you (including one hand in the pocket) when checking my amps.  After 40 years working in a power plant and seeing some dreadful 'faults', I leaned one thing.  You make most mistakes in an amp......ONE time!
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G3RZP
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« Reply #19 on: August 03, 2016, 05:08:16 AM »

Al,

Quote
You make most mistakes in an amp......ONE time!

Yet I get the impression that there have been more hams electrocuted over the years by unwittingly putting up antennas that contact overhead power lines than by transmitters!
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WA2ISE
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Posts: 879




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« Reply #20 on: August 03, 2016, 06:40:49 AM »



Yet I get the impression that there have been more hams electrocuted over the years by unwittingly putting up antennas that contact overhead power lines than by transmitters!


I wouldn't put an antenna near powerlines because of the QRM powerlines generate. 
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K8AXW
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« Reply #21 on: August 03, 2016, 09:30:56 AM »

Quote
Yet I get the impression that there have been more hams electrocuted over the years by unwittingly putting up antennas that contact overhead power lines than by transmitters!

Peter:  You could very well be correct.  However, amplifier accidents seldom get news coverage because most people have no idea what an amplifier is.  Whereas most know what an antenna is.  Since antenna electrocutions involve the power utilities, they get the news coverage.

We had two drunk CB'rs near here buy the farm when their roof mounted (while mounting it) swung over and came in contact with about 18,000V.

I would hazard a guess that many amp owners have no idea of just what they're dealing with when they get to probing around, especially with the incorrect or inferior test gear.  (This is why I usually comment when the subjects of amps and meters are posted here)

A good friend of mine who had been a ham for over 50 years just about bought it when he came in contact with 1200VDC in his homebrew amp.  At the time he was about 75 years old and in bad health.  He was never the same after that when it came to working on his gear.
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G3RZP
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« Reply #22 on: August 05, 2016, 04:08:47 AM »

Al,

Totally OT.........But there's a report available about a fire on a train in the Channel Tunnel. The equipment for detecting something sticking above a truck didn't detect a CB antenna and it touched the overhead catenary as the train entered the tunnel. A lovely flash can be seen on the TV images and the whole truck cab  caught fire and burned up!

https://www.gov.uk/raib-reports/fire-on-board-a-freight-shuttle-in-the-channel-tunnel
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