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Hit with 6kv yesterday... DON'T trust the Millen connectors!




 
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Author Topic: Hit with 6kv yesterday... DON'T trust the Millen connectors!  (Read 8710 times)
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WBear2GCR
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« Reply #25 on: December 18, 2018, 09:54:25 PM »

The ubiquitous 7-16 metric coax connector system works very well for HV, is dirt cheap, too.

Good to hear you'll be OK.

73DG

Have to admit, I do not know what that is!

Pix of that connector??

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W1ITT
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« Reply #26 on: December 18, 2018, 10:15:49 PM »

If you do a search on ebay for   7-16 DIN, that will get a few examples of the connector.  It's available for various cables and they have chassis mounts, as mentioned, all good for HV and easy to work with.  The connector is metric, and it's not " seven sixteenths" as some call it erroneously.  Cool people just say " seven sixteen din".  The two numbers refer to the size of the inner and outer parts in millimeters.  It's a good RF connector, used by many of the moonbounce boys on arrays and dishes.   I have used them in UHF TV omni panel arrays.
It's only specified for 3 kv dc and 4 kv rf, but it hipots much higher, and it won't jump out and grab you like that Millen connector.

http://www.spectrum-et.org/new_web2/adapters/pdf/InSeries/Inseries-7-16.pdf
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« Reply #27 on: December 19, 2018, 08:29:00 PM »

Thank God you're OK, Shane.  We need your wisdom and wit here... I don't think I've ever read one of your posts where I haven't learned something.  And this episode is no exception.

Thanks for sharing your experience. 

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WBear2GCR
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« Reply #28 on: December 20, 2018, 09:18:30 AM »

Henry used the pin jack setup for HV on some of the early 2K-3 amplifiers... They used a phenolic sleeve @ 3kv.
I rebuilt it (it was broken) using Delrin that I machined.

It fits into a corresponding connector that has the pin surrounded by a tube of phenolic, now delrin... of course
it is NOT as configured a positive locking connector. Could be made to do that, with minor mods...

The stock pin jack ends up down in the threaded delrin rod.

Sorry all I have is the 150x150px image... it's from 20 yrs back.


* HV-CONNECTOR-150jpg.jpg (4.7 KB, 229x162 - viewed 96 times.)
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« Reply #29 on: December 20, 2018, 12:14:19 PM »

7-16 DIN info:

https://en.wikipedia.org/wiki/7/16_DIN_connector

Great for RF,  as well,   and as Dennis mentioned,   dirt cheap.

FWIW,   Vic
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K1JJ
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« Reply #30 on: December 20, 2018, 12:38:25 PM »

Lest we forget....

A plate modulated rig like a single 4-400A at 3KV under heavy modulation can have 6-8KV peak voltage or more... [+ dirt arc factor]  on a HV jack/plug going into the RF deck.

Linear amps are more predictable, though 6KV DC (the topic here) is dicey.

I maintain it takes extraordinary measures to safely route HV above 3KV.

T
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
WD5JKO
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« Reply #31 on: December 20, 2018, 02:51:14 PM »

  A modified PL-259 / SO-239 can be easily made to handle 6KV DC. Plain old RG-8 Coax (non foam insulation) can handle a lot more.

I attach a picture of the concept.

This requires some fabrication and machining, but a doable solution.

A HVDC Power Supply maker, Glassman uses this approach on a variety of products. The company I work for buys a 40KV supply that uses this approach. The RG-8 coax handles 40KV DC (not RMS AC) for years without failure. The 40KV application has the center conductor extended 14" from the connector!

This approach done proper will remove the safety hazard so prevalent with the Millen.

Jim
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* Modified_PL259.jpg (254.91 KB, 935x860 - viewed 161 times.)
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K1JJ
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« Reply #32 on: December 20, 2018, 03:40:22 PM »

 A modified PL-259 / SO-239 can be easily made to handle 6KV DC. Plain old RG-8 Coax (non foam insulation) can handle a lot more.

I attach a picture of the concept.

This requires some fabrication and machining, but a doable solution.

A HVDC Power Supply maker, Glassman uses this approach on a variety of products. The company I work for buys a 40KV supply that uses this approach. The RG-8 coax handles 40KV DC (not RMS AC) for years without failure. The 40KV application has the center conductor extended 14" from the connector!

This approach done proper will remove the safety hazard so prevalent with the Millen.

Jim
Wd5JKO

Now dat's wat I is talkin' bout, Jim! That is by far the BEST HV connector solution I have ever seen. It even uses the shield as a saftey feature....  cut the cable and you have an automatic short circuit to pop the breaker. And brickhouse mechanically secure.

When I build a new HV rig, the connector, cable and feeder will look like that.

Thanks for sharing it, OM!


BTW, yes, foam coax is NG for HV. I have arced it over before. Stick with the high quality (RG-213 is a good example)  clear plastic insulation as you suggested.

T
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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« Reply #33 on: December 20, 2018, 05:29:53 PM »

'cept for one little thing... I don't know about yooze guyz, but I do not want ANY HV on an exposed
metal plug! The banana type plug shown on the end of the coax is fine when it is connected, but
waving around a hot end, not for me. So, I'd want a FEMALE looking thing that has no easy and
direct path to the HOT conductor. That looks like the reverse of what I'd like to see.

So, that's fine for a "goezouta" not a "goezinta"!

Opinions?

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W1ITT
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« Reply #34 on: December 20, 2018, 06:27:37 PM »

I gotta agree with the Bear on that one.  HV needs to be recessed, at least a bit.  I know we all mean to be careful, but if the breaker on the HV supply is inadvertently left on, and the remote start switch (if you have one) get activated, there's trouble exposed.  At 2 AM local time, dumb stuff sometimes happens.  I'd rather see an HV line go in through a cable clamp and be permanently connected in both the HV enclosure and the RF/modulator deck.  It would be a pain and more time consuming to work on, but it could be very inexpensive, and effective.
I'm trying to think if I ever saw a commercial transmitter that had a removable connector on the HV line.  Nothing comes immediately to mind. 
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KK4YY
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« Reply #35 on: December 20, 2018, 07:22:30 PM »

Even shielded cables aren't fool proof. Try to connect one with the power on and the shield as the only return path and ZAP. Not only does it need a recessed female end, but it should make-ground-before-hot and break-hot-before-ground. Of course, a separate DC return should always be used, but accidents happen. The best bet when using a separate power supply is to put everything in an enclosed rack cabinet. That will keep you, the kids, and your pets, far from high voltages.

But even the best safe guards aren't total protection. Treat every microphone as if it's on. Treat every conductor as if it's hot. Treat every  gun as if it's loaded. Safety is more in your head than in the engineers design.

Don
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« Reply #36 on: December 21, 2018, 11:59:47 AM »

Isn't it best to use connectors rated twice the expected voltage for safety?
I hate guesswork where stuff can go boom or the grim reaper lives inside.
These may not be for everyone. Not coaxial but the ratings are up there.
The plug is long and goes way into the socket and they have chassis mount.
http://hvstuff.com/high-voltage-connectors-plugs-sockets
There are others I suppose but these give you both sides of the connection.
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K1JJ
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« Reply #37 on: December 21, 2018, 12:12:21 PM »

I think Jim's idea is a good step in the right direction to getting us thinking about better HV safety.  Over the years, I've seen a lot of ham homebrew rigs. Some can be downright dangerous, especially when you look at the exposed backs of some plate modulated rigs with HV wires running from mod iron, chokes, power supplies, etc... and unshielded HV inter-connections between racks out in the open.

But then some rigs are very well done and safe. My test is this: Pretend the HV is on -  try as you may - can you touch any HV?  Can a cat or dog or child find a way to work his way into the HV if he tried?

I agree that a female banana  plug on Jim's example would be a better idea, though if there were 6 KV LIVE on a female banana plug, it would probably rock you badly if you touched it, recess or not.

I like the idea that when assembled, there is no way for Jim's plug assembly to work loose or pull out, be touched accidently, is shielded well and is so far above the required voltage, (40KV) it will (almost) never fail. (And remember to include the extra ground wire.)

Yes, commercial rigs often have permanant connections because they get installed for a long time. But most ham gear, computers and other rigs are meant to be moved from time to time and most will strip bare of cables when moved.

This homebrew plug example may cause many of us to break out of the box of old habits - Maybe we have not  been as safe as we should be.  Even though my shack passes the HV cat/dog test and uses shielded HV cables, I am looking at HV safety in a somewhat different light now.

T

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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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« Reply #38 on: December 21, 2018, 12:25:32 PM »

Really ANY HV interconnection should be made of a screwed-on ground wire AND COAX. The BNC HV coax connectors are cheap and plentiful.  They withstand 5 kV
ANY damage of the isolation or cable will result in a HV short and the HV can never be exposed. A minor damage will expose the grounded shield, not the HV
A normal HV cable will be very dangerous when damaged.
An RG58 and the BNC HV connectors will make a low cost and safe HV connection.
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Detroit47
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« Reply #39 on: December 21, 2018, 03:20:37 PM »

When I build a box that is two pieces. I treat it like any other piece of industrial equipment. The high voltage cable is inside conduit which is grounded. I use the flexible stuff no mice kids or customers can get at it. Plus I don't get sued for building a death trap. The connections are inside the cabinet either bolted or soldered.


http://www.afcweb.com/flexible-metal-conduit/


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« Reply #40 on: December 21, 2018, 05:38:56 PM »

I am glad you are above ground.

Yeah, 6 KV above ground  Grin

Good to hear you survived!  Cool And watch for delayed tissue injury, as I'm sure your doc has already briefed you. HV burns and high-pressure injection injuries are always worse than they appear initially.

Quote
A HVDC Power Supply maker, Glassman uses this approach on a variety of products.

I have a Spellman 60 KV x-ray power supply that also uses this approach. Not designed for long-term continuous use. The jack is recessed all the way inside the "brick" and the SO-239 thread is on the other end. About 8-9" of poly RG-8 leakage path.

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WBear2GCR
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« Reply #41 on: December 21, 2018, 05:42:07 PM »


The plug is long and goes way into the socket and they have chassis mount.
http://hvstuff.com/high-voltage-connectors-plugs-sockets
There are others I suppose but these give you both sides of the connection.

These look nice, but they'd be for a cable that was fixed on the RF deck side (or modulator)
and coming FROM the PS chassis. Perfect.

Going the other way, they don't seem to have a cable mounted female/chassis mounted male??

And as you noted they are not coaxial type... but one could use cable with a braid on the outside?

----------------------

DON, were you saying that in the case of HV DC on a coax cable that only has the braid grounded
on one end that it will try to arc over?? Not sure about your earlier comment...
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« Reply #42 on: December 21, 2018, 05:47:53 PM »

When I build a box that is two pieces. I treat it like any other piece of industrial equipment. The high voltage cable is inside conduit which is grounded. I use the flexible stuff no mice kids or customers can get at it. Plus I don't get sued for building a death trap. The connections are inside the cabinet either bolted or soldered.

http://www.afcweb.com/flexible-metal-conduit/

John N8QPC

Looks a lot like old school BX??

"gooseneck" material that they use on lamps might be interesting too... but for most applications
with semi-rigid stuff one is going to need a 90deg adapter at the ends, maybe not the best way to do things??

Then there is the flex natural gas line stuff too...

I'd be more apt to use a braid over HV rated wire.
I have 50kv rated silicone wire here. About the same size as RG-8 core, maybe slightly
fatter... I think a wire braid over the top ought to be pretty much safe??
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« Reply #43 on: December 21, 2018, 06:01:56 PM »

Bear,
DON, were you saying that in the case of HV DC on a coax cable that only has the braid grounded
on one end that it will try to arc over?? Not sure about your earlier comment...
If the coax braid were being used as the only return for the DC, then disconnecting it (a PL259), you'd be breaking the ground connection first. If you had one hand on the connector shell and the other on the chassis... bad news.

Don
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K1JJ
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« Reply #44 on: December 21, 2018, 08:12:38 PM »

If the coax braid were being used as the only return for the DC, then disconnecting it (a PL259), you'd be breaking the ground connection first. If you had one hand on the connector shell and the other on the chassis... bad news.
Don



This is a very important point worth exploring further!  I have brought this up in the past and it could be the most under-rated safety guideline - that many hams do not fear...


We all put lots of care into our hot B+ lead installation.  We all make sure it is isolated both electrically and mechanically - and for good reason.

Now look at the other part of the circuit, the ground wire or B minus.   As Don said what if the ground wire gets broken OR we forget to hook it up? Considering that a lowly, bare ground wire never gets the respect it deserves, isn't it possible to make this error?


I have a question about this:

Let's take a regular linear amp. The HV B+ is basically connected to the plate of a pair of 3-500Zs. In series with the tube's plate is a near-vacuum, essentially 10? megohms or more to ground if the tube is off or unkeyed.

Let's say the chassis is floating, not grounded. (you forgot to connect up the gnd wire B- and coax connector gnds, etc. )  Now if you put you hands across the chassis and the station ground, your body will be in series with the HV supply, in the negative lead.  X amount of voltage will drop across you depending on the ratio of the tube's vacuum and the resistance thru your arms.  Let's say you are 200K and the tube is 10 Meg+.   This puts about 60 VDC across you, not too bad.

Now, what if the tube gets keyed and drops its internal resistance... You are still 200K and the tube will struggle to drop more voltage across you.  The question is how much of the 3KV stays across the tubes with your body's series resistance of 200K?     At 200K this is 15 ma at 3KV, deadly current if the tube is keyed. Or will the 200K put the tube near cutoff and draw near zero current thru your body?   -  Am I missing something?

My point is, what are the voltages and currents involved when we get in series with the negative lead of a  standard 3KV supply into a typical linear amplifier?  Is this lowly ground wire a deadly concern we should pay more attention to?  

I suppose one way to find out for sure is hook up a 200K resistor in series with the gnd wire and measure the current and voltage across the resistor with the amp both keyed and unkeyed.  

T
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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« Reply #45 on: December 21, 2018, 10:26:07 PM »

And that's the reason that you ALWAYS need a screwed-on ground wire for safety return. And you also have the ground of the coax HV wire, but thats the safety in case of damage to the HV cable.
I used this years in big RF generators and never had an issue.
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« Reply #46 on: December 22, 2018, 12:10:54 AM »

Admittedly, I get a little lazy about using the 10-32 grounding stud on the back of radios. A wingnut makes it a bit easier, but it's always a darn reach-around knuckle-scrapping operation that I sometimes "forget" to do. Knowing that I'm not 100% compliant with this basic requirement, I have an alternative.

On units I've built, and old boat anchors, I like to install the very common chassis mount "computer" type AC connector, IEC 60320 standard. I did this recently with a DX-100 that I'm modifying. Those connectors have a ground terminal that "makes" before the line and neutral (the ground pin is longer). The cord-set is removable, which is a blessing in itself. When servicing the radio, pulling the cord-set from the back of the rig is a good way to make sure the power source is removed, literally. These chassis mount AC inlets can be had with built-in fuses and/or RFI filters. Some even have a switch.

As an alternative to a nice heavy braid ground-strap these connectors aren't perfect. Probably not very good from an RF grounding standpoint, but pretty good for AC safety grounding. As far as I'm aware, no one has died from having a poor RF ground (not that it's not important).

So, to the point at hand, having a continuous AC ground provides a path for a broken high voltage DC return.

Two-wire non-polarized AC cords need to go.

Don
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« Reply #47 on: December 22, 2018, 11:39:43 AM »

The question still remains...

Using a remote 3KV supply to power a  3-500Z linear amplifier or class C tube amplifier...  If the B minus DC ground return is broken and a human body is put in its place, (200K)  is this a lethal situation?


My current thinking is  NO....   because the 200K is in the cathode lead of the amplifier tube and acts like a big biasing resistor to cut the tube off, thus no current flow. (just like a big Zener diode normally does in the cathode)  No matter if we key the tube on or drive it with RF, the tube is still cut off with such a big cathode biasing resistance -  and the B+ 3KV drops across the tube safely and not across the "cathode resistor" human body. (with minimal "bias" shock)

Can someone tell me I'm wrong and why?

T
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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« Reply #48 on: December 22, 2018, 01:41:19 PM »

Tom,

I mostly agree. Probably not lethal, but probably a noticeable shock. Either way, I don't want to be a part of that circuit. What if one were operating SSB and got a small, non-lethal shock under the circumstances that you describe, that caused the usual "Ahhhhhh!" to be uttered, which then keyed the VOX. Suddenly it's not a small shock anymore.

This reminds me of a favorite movie scene from No Country for Old Men:
Llewelyn Moss: Just lookin' for what's comin'.
Poolside woman: Yeah, but no one ever sees that.

Don
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« Reply #49 on: December 22, 2018, 02:18:27 PM »

Tom,

I mostly agree. Probably not lethal, but probably a noticeable shock. Either way, I don't want to be a part of that circuit. What if one were operating SSB and got a small, non-lethal shock under the circumstances that you describe, that caused the usual "Ahhhhhh!" to be uttered, which then keyed the VOX. Suddenly it's not a small shock anymore.

Don


Hi Don,

Thanks for the reply -

Well, I'm sticking my neck out and saying that with a 200K human body cathode resistor in the B minus, it doesn't matter if the tube is keyed, driven hard or not....  the tube is so hard-biased-off it will not draw any meaningful current to produce a B+ drop across the 200K.  There will be a "bias" voltage generated for a small jolt, if any.

It's like when we key the cathode of a linear tube to ground. When it is unkeyed, there is no soaring voltage on the cathode. This is essentially breaking the B minus.  We may use a 50K clamping resistor there, but it's only a technique to keep relay contact sparks at bay when keying. Notice we can also get away with 1KV .01 caps from cathode to ground.

I'm thinking this is why we don't hear about 50% of ham HV fatalities caused by broken ground returns and 50% caused by accidental contact between B+ and chassis.  They are almost all caused by B+ contact.   The occasional ground break fatality can happen with rock stars on stage getting 240VAC jolts, but the ham amplifier  B-  break is a different situation.

Hey, you can bet I will continue to treat B- like B+ with respect... it's just that I want to understand what is really going on and not unduly fear something that is not really there.

T



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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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