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Author Topic: Use of an SO-239/PL-259 as a high voltage connector  (Read 4104 times)
NZ5N
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« on: March 26, 2011, 05:05:37 AM »

Hi,

Last year at my summer QTH in Slovakia I bought a homebrew GS-35b amp for 2 meters.  It came with a separate 3200v 1 amp power supply, which was connected to the amp with a piece of RG-213 with a PL-259 on each end, with an SO-239 on the back of each chassis.  At the time, a couple of my Slovak ham friends said that was not a good idea, as the HV could flash over with these connectors.  I used the amp all summer and did have have any problems.

I'm now getting ready for Slovakia 2011 and am wondering if I need to do anything.  Should I live with the PL-259s or are they dangerous enough to warrant changing?

73, Bill NZ5N
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G1YHE
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« Reply #1 on: March 26, 2011, 05:29:20 AM »

Please change that very dangerous set up.

High voltage requires the correct connectors.

73 Denis G1YHE.

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W8JX
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« Reply #2 on: March 26, 2011, 05:40:46 AM »

Please change that very dangerous set up.

High voltage requires the correct connectors.

73 Denis G1YHE.



I agree as the biggest danger here is the potential for very high voltage on a exposed PL259 end on it or being hooked up improperly.  The 213, while not the ideal choice here, is not the issue as much as the connectors are.
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AD4U
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« Reply #3 on: March 26, 2011, 05:49:11 AM »

213 will easily handle this voltage.  Under less than ideal conditions, the PL259 / SO239 will not.

Dick  AD4U
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KE3WD
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« Reply #4 on: March 26, 2011, 06:00:13 AM »

Mistaking it for an antenna connection would prove fatal. 

Multiply that by a factor of ten when contemplating use in a Contest Station environment, where mistakes are made in the heat of contesting and fatigue. 


The Millen HV connector with proper HV wire is recommended here. 


73
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N3OX
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« Reply #5 on: March 26, 2011, 06:34:13 AM »

I think your amp builder may have had some confusion about a typical practice (one that is, IMO, fairly safe in and of itself) for use of big coax cable as HV cable.  

I've seen a lot of solid dielectric coax cable of the RG-8 size used as shielded high voltage wire, with SO-239 and PL-259 SHELLS used to make the ground connection between boxes, but the connector pins and dielectric are not used.    The center contact and dielectric of both connectors are pulled out (or drilled) , and a long section of jacket and braid is stripped off the coax.  Then the HV connection is made somewhere inside the box far from grounded stuff.

Here's a picture:

http://www.timefracture.org/laserpics/coaxconns.jpg

In this case, the dielectric of the connector has been drilled to be a close fit on the dielectric of the cable.

This is a lot different than using a PL-259/SO-239 as a HV connector, but someone who saw that picture in a fully assembled state maybe wouldn't realize the difference, and then might use a regular connector pair as a HV input.

Even though I think the extended-dielectric PL-259/SO-239 shell setup is fairly safe, I do agree with KE3WD that at a station that other people were using, there's a chance for dangerous confusion between connector types.  I maybe would go for a connector that doesn't even look like  an antenna connector from the outside.
« Last Edit: March 26, 2011, 06:39:28 AM by N3OX » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
NZ5N
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« Reply #6 on: March 26, 2011, 08:16:38 AM »

Thanks for the replies.  In Slovakia, I do not have access to a work bench.  Is there any type of safer connector that would fit into the existing holes for the SO-239?  It would be tough for me to drill new holes in the chassis.

I should note that the builder apparently recognized the risk of confusion and at least painted the HV cables and connectors red.

73, Bill
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AC5UP
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« Reply #7 on: March 26, 2011, 10:36:27 AM »

As a general rule female HV connectors have their metal contacts buried deep in the insulation and the voltage source is always on the female side. The design assures no exposed pins will ever have voltage on them no matter how careless the operator might be. The HV cable you're now using is a 911 call waiting to happen and at 3200V / 1A the EMT's won't need the lights or siren for the trip to the hospital.

As for what's available to upgrade your situation, Google can help with that. Buy the good stuff for this cable.

BTW: I've been known to watch Noviny TV Joj on joj.sk and can usually follow what's going on even though I'm at something like 20% fluency. If you ever come across Janka Krescanko-Dibakova in your travels let her know she has a fan in the great beyond. Something about the glasses with those big blue eyes works for me............   Roll Eyes
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NZ5N
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« Reply #8 on: March 26, 2011, 04:55:44 PM »

Good old Janka, I probably will see her, Bratislava is not a huge city.

Well, I can see why he used a PL-259.  HV connectors are not cheap, like these for $139 from Surplus Sales:
http://www.surplussales.com/wire-cable/Voden/Voden-SHV_Connectors.html.  That's a week's salary for the average Slovak.  Surplus Sales also has relatively cheaper HV connectors, but even the Millen connectors, which I've heard are not the best, are $20 and up per pair (not sure why the yellow ones are so much cheaper than the red and black.  And these appear to be single wire connectors, where does the B- connect to?

I have not seen anything that would could be substituted for an SO-239 without drilling or modifying the chassis, suggestions welcome.

73, Bill
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W8JX
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« Reply #9 on: March 26, 2011, 06:01:55 PM »

Well in a pinch how about a Teflon "N" connector as it will handle voltage and you will not be able to cross it with a 259
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NZ5N
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« Reply #10 on: March 26, 2011, 07:56:23 PM »

One guy came up with an interesting HV connector.  It's a standard AC 240v power plug, with both prongs attached to the center conductor of a piece of RG-213.  The shield of the RG-213 is attached to a piece of wire that goes to the ground terminal.  See a photo at: http://www.myhamshack.com/HamShackPictureViewer/7309/HV-plug-for-2m-amp.aspx 

Even if this is considered safe, I don't think a matching female socket would fit into my power supply in place of the SO-239.
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W8JX
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« Reply #11 on: March 26, 2011, 08:40:53 PM »

One guy came up with an interesting HV connector.  It's a standard AC 240v power plug, with both prongs attached to the center conductor of a piece of RG-213.  The shield of the RG-213 is attached to a piece of wire that goes to the ground terminal.  See a photo at: http://www.myhamshack.com/HamShackPictureViewer/7309/HV-plug-for-2m-amp.aspx  

Even if this is considered safe, I don't think a matching female socket would fit into my power supply in place of the SO-239.

I do not like this idea as dielectric is not rated for that voltage while the teflon in a N connector will handle the voltage if it has too.   Plus you have two big potentially  hot prongs sticking out
« Last Edit: March 26, 2011, 08:43:21 PM by W8JX » Logged

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WB2WIK
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« Reply #12 on: March 26, 2011, 09:54:24 PM »

PL-259s, especially the Teflon insulated ones, will handle several thousand volts just fine.

But standard practice is to use the female on the end of the HV wire, plugging into a male on the chassis; thus leaving "exposure" to HV on the end of the cable much less likely.

MHV connectors which look like BNCs (but are not) are a pretty good choice, and they're not expensive at all ($5 each or so).  They're a little bit smaller than UHFs, so to fit one in a chassis already punched for a UHF connector would require a filler plate, which could be as simple as two large flat washers punched with the right sized holes, one one each side of the chassis wall.

I've mostly used Millen 7kV HV connectors on most of my homebrew amps for many years, because they can handle the application and are also cheap (just a few dollars each, and still readily available).  However they are not shielded and do not carry the ground return at all -- they're just single contact connectors, so a ground has to be provided separately.

The Millens aren't "perfect," but they are cheap and will handle up to 7kV at 1 atmosphere.  I've had them in amps I built in the 1960s and they still work after 45 years.
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NZ5N
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« Reply #13 on: March 27, 2011, 03:05:22 AM »

Thanks for the replies.  Steve, where can you get MHVs for $5?  Surplus Sales has the best price I've seen, $18 for a male-female set: http://www.surplussales.com/Connectors/MHV.html

Is there any difference between the Millen 37001 ($18 a pair from http://www.rfparts.com/hvconnector.html) and the Millen 37501 ($20 a pair for yellow, $28 a pair for red or black from http://www.surplussales.com/wire-cable/hvwire-2.html)?

73, Bill
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WB2WIK
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« Reply #14 on: March 27, 2011, 01:28:58 PM »

Thanks for the replies.  Steve, where can you get MHVs for $5?  Surplus Sales has the best price I've seen, $18 for a male-female set: http://www.surplussales.com/Connectors/MHV.html

Is there any difference between the Millen 37001 ($18 a pair from http://www.rfparts.com/hvconnector.html) and the Millen 37501 ($20 a pair for yellow, $28 a pair for red or black from http://www.surplussales.com/wire-cable/hvwire-2.html)?

73, Bill

Hi Bill,

I have an industrial account with Force Electronics and buy MHVs for $4.95 each.  Not sure what the "retail" price is supposed to be, but "Surplus Sales" has zero good deals that I've ever found.  The Millen from RF parts is the same as the Millen from Surplus Sales; Surplus Sales just charges more.  P.T. Barnum was right about suckers.  I have a lot of the red colored Millen males and females, purchased from Apex Electronics in Sun Valley, CA for $9 a pair a few years ago.
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