help me not get shocked

[KD5TXX]

I am running a hallicrafters ht 37 and hamarlund Hq 145.  Today I had the ht37 unplugged from all power and the dowkey unplugged.  I was hooking the coax from antenna to dowkey and from transmitter to antenna.  When I grabbed the coax from the receiver I felt the electricity in my fingers.  I checked and was seeing 56 or so volts when I touched the two.  I unplugged the receiver and reversed the plug and replugged it and got the same result.  Can someone help.me out?

[Pete, WA2CWA]

The receiver has .01 mfd capacitors from each side of the AC line to ground. One or both are probably leaky and should be replaced.

[w1vtp]

The receiver has .01 mfd capacitors from each side of the AC line to ground. One or both are probably leaky and should be replaced.

Yup!  I've noticed that a lot with old gear.  Even HP test equipment with the round pin line connectors had a problem with the ground lifting internally (probably a compression connection letting go). That problem went away with the advent of the newer line connectors

Makes a case for a common ground between equipment.  I've included a couple shots of the copper pipe system I use. In any case, make a common connection between all station equipment

Al

[KA2DZT]

All your equipment should be grounded together including all your coax lines coming from your antennas.  Check or replace those caps that are on the AC line in the receiver.  If you can't replace them, cut them out, you don't need them anyway.  Any piece of equipment that has a power xfmr, reversing the plug will not change anything.

The shock is caused by multiple grounds that are not bonded together.  Also as previously mentioned by Pete, those AC caps on the AC line (in the equipment) may be leaky.  Replace them or get rid of them, as they can be a source of trouble.

Follow Al's tip, your should have a common ground buzz that all your antenna coaxes have their shields grounded to along with the chassis of your main equipment.  You can't always rely on a 3-wire plug for grounding the equipment.  Add separate ground wires from the equipment to the ground buzz.  This is especially important on old gear with only a 2-wire plug.

Don't electroplate yourself.

Also as a side note, if you see smoke, you made a mistake

Fred

[WA1GFZ]

AC flows through a cap limited by reactance.

[W2VW]

Those caps will produce a bad feeling even when they aren't leaky.

[ke7trp]

What I am reading is that you had a coax line hooked to the RX and you grabbed the other end with your hand. If this is in fact what you did, This is considered normal. Replacing the caps wont remove the voltage at the coax connector.  Its not grounding on the station.

You can take a receiver/radio lay it on the table alone, Plug it in and measure the voltage there at the coax connector.  Many, many of us have had that low volt shock.  Just remember to push the coax into the connector while not touching the radio or connector, Once its pushed in, Simply screw the connector on. The point is to make the shield connection from coax to the radio and DO NOT bridge that connection with your body or finger


The worst of the group for this is the FT101.  There you will find a full 90+ volts at the connector and it will light up   Out of the many many 101s I have owned, worked on and or aligned, They all have big voltage there.

The confusion from some posts here is a very real issue where you have a non polarized 117 volt two wire plug and failed/leaky caps.  This can cause voltage to appear on the case of the radio.  This can be removed by simply reversing the power plug. 

Most of us Install a 3 wire power cable/plug and properly hook the hot and neutral with in the rig.  Some rigs do not have a power transformer/isolation transformer.  I had an RME with no trans in it. These can be deadly if the caps are bad and the plug is backwards.   I was warned about this before I set out to repair it and sure enough mine had voltage on the case,  Had I touched the radio, I would have been lit up.

To measure if you do have voltage on the case of the radio, you simply hold the negative lead of your volt meter in your hand and touch the red lead to the case,  Voltage?  Flip the plug.  No voltage?  your good.   I have done this test hundreds of times. 


C

[KA2DZT]

Clark,

What are you talking about??  It's not normal to have a voltage difference between the receiver and the coax lines.  If you do, it's because things are not properly grounded and/or bounded together.  Your coax lines even when not connected to your equipment should have the shields grounded to the station ground.  The equipment is then also always grounded to the same ground point.  When you do this there will be no voltage between antennas and equipment.

Most ham equipment have power xfmrs which eliminates the need for polarized plugs, reversing plugs will make no change.  Of course equipment without power xfmrs are always a problem and in my opinion should not even be used without an isolation xfmr.  Especially when being used with external antennas or even connections to other pieces of station equipment.

As for the caps on the AC line, these things should be replaced with disc ceramics that are very reliable.  Paper AC caps on the line should be removed.  I would just remove any cap that was on the AC line to ground,  they're a disaster waiting to happen.  They're not needed anyway.  Of course there are caps that are specially designed to be across AC lines.  Most all modern TVs and like products have them as part of the line filters.

Fred

[w3jn]

ANY line bypass capacitors - leaky or not - will produce an AC voltage on an ungrounded chassis.   Remember, capacitors pass AC according to their reactance at a particular frequency.  As Frank noted the current is limited by the capacitive reactance.

For your .01 uF capacitors the reactance at 60 hz is 265K ohms.  And the reason you have 56 volts on the chassis is because you have capacitors on both sides of the line, acting as a voltage divider so you have the line voltage /2.  Just ground the chassis to the AC power ground and you'll be good to go.  DO NOT just ground it to another ground, unless that ground is bonded to your service entrance ground.

[KD5TXX]

To clarify.  The Chasis has no voltage on it.  It is the coax.  I touched and checked the actual receiver and got nothing.  It is when I touch the coax connector that I get a reading...and tingeling..

[KA2DZT]

To clarify.  The Chasis has no voltage on it.  It is the coax.

Ground your coax shields to the station ground.  Your station ground should also be grounded to your AC panel ground.  If you have a ground system for your antennas that is grounded in the earth that is not the same ground point as your AC service ground, this is a problem.  If you do, you should bond the two different grounds together.  Use at least a #6 copper wire to connect the two grounds together.

I run all my coaxes into the shack through connectors that are grounded at the entrance point.  I disconnect the short piece of coax that runs from those grounded feed-through connectors to the station equipment.  As you can see my coax antenna lines are always grounded regardless if they're connected to the equipment.

To look at the two .01 caps on the AC line to chassis,  I would get rid of them, they're not needed and can be a problem if they short or become leaky.  Non of my station receivers or xmtrs have them.

Fred

[ke7trp]

Kd5txx. They are stuck on the problem being ac on chassis. What u are seeing is a common situation with alot of older gear. You can go in and replace all of the bypass caps in the rf section and possibly alter the circuit or, you just be aware of the issue and dont bridge the coax shield with your hand.

[w3jn]

To clarify.  The Chasis has no voltage on it.  It is the coax.  I touched and checked the actual receiver and got nothing.  It is when I touch the coax connector that I get a reading...and tingeling..

There is a voltage potential between the two and you don't know which one is the source of the voltage.  Check the AC voltage between the RX and AC power ground when it's plugged into the wall but nothing else connected to it.  Do you see voltage?  If not then the problem lies elsewhere.  Perhaps the Dow Key's coil is leaking to ground.   Or the antenna is connected to something else that has an AC potential on it.

Clark, nobody is telling him to replace bypass caps in the RF section.  We're talking about the AC line bypass capacitors.  And they're there for a purpose.

[ke7trp]

For some reason you want to argue with me when I have done nothing wrong here. What I am understanding is the man is talking about is the potential from the center of the coax to the shield of the coax on the RX'r.

Now, If you have gone your entire ham life and not ever been shocked from a coaxial cable that is inserted into an old Radio, you need to put a meter across the center to shield to witness this voltage.

Some recievers have a COVER over the terminals so you do not get shocked.  Why? Cause there be fire dare man!

I am not saying that anything you said about the line bypass/voltage on chassis issue is wrong.   What I am saying is that this man is clearly talking about being shocked while holding the end of a coaxial cable he unscrewed from the dow key that ran to the RXer.  Many radios have voltage there.

I am sorry if I confused you and I did not want to make you upset man. I think everyone thought about the old two wire plug issue and jumped on that as a problem/solution. When clearly, This is a seperate issue.  

Sorry if I seem edgy today. My hero Andy Griffith died today.




C

[Pete, WA2CWA]

To clarify.  The Chasis has no voltage on it.  It is the coax.  I touched and checked the actual receiver and got nothing.  It is when I touch the coax connector that I get a reading...and tingeling..

You say "I touch the coax connector and get a reading" - Are you referring to the barrel of the connector? And, you're reading this voltage from what point (what physical thing) to what point (what physical thing)? Are you defining this voltage as AC or DC as per the meter reading? Everyone is making the assumption it's AC.

The HQ-145 has three screw terminals for antenna termination. They're labeled A - A - G. A set of frequency defining input coils are chosen by the band switch. At each position, one side of the coil goes to the left A, the other side of the coil goes to the middle A. They don't go anywhere else except that the calibrator output lead is also connected to the left A. If the calibrator coupling cap. was leaking some DC voltage might appear on the left A terminal, but receiver has to be powered up, calibrator has to be on, center A terminal has to be ungrounded. If you're using coax, the center conductor would connect to the left A and a mechanical bridge goes between the middle A and G and your coax shield is connected to both of them.

If you're getting a voltage reading from the barrel or center connector to some physical thing which you haven't yet defined and no voltage from the chassis to the thing you haven't yet defined, I'll leave the answer(s) up to the mentalists.

[KD5TXX]

I will try to take pictures and explain later.  Was just told I have to go shopping now...

[W1RKW]

I will try to take pictures and explain later.  Was just told I have to go shopping now...

or maybe draw a schematic of your setup. 

[vincent]

Maybe it's the voltage of the electrostatic charges accumulated by the antenna? Of course not 56 volts!

[N4zed]

Maybe it's the voltage of the electrostatic charges accumulated by the antenna?

Probably not a sustained voltage of 56v. It takes something like 5000 v before you can "feel" a static shock.

Ken
N4zed

[K3ZS]

Help you not get shocked-unplug everything-connect your coax connectors-plug everything back in.