Hum on my carrier w/ Henry 2K-4

[KX5JT]

I just acquired a Henry 2K-4 console linear amplifier.  The Henry is rated for continous duty and  AM. I'm very satified with the output from the two aging Eimac 3-500Z's but the 120 cycle hum that rides on the carrier is troublesome. It's there whether I'm using my Kenwood TS-570 or my modified Heathkit DX-60 to drive it. When I use the DX-60 (which I prefer for AM) making adjusting the tuning control will change the amplitude of the hum but never reduce it enough. Seems like when in resonance the hum peaks too. I have grounded the amp and the DX-60 via 10 gauge solid copper to an 8 gauge solid copper coming into the shack that's attached to the 8 foot copper clad steel ground rod right outside a couple feet away.
 
For some perspective, I have no audible hum from the Heathkit SB-200 and everything else the same. The SB-200 is setup for 120 volts however, not 220/240.
 
The Henry has full-wave bridge rectifier then uses an 8 henry (700ma) filter choke with an oil filled .1mf (7500v) in parallel then an oil filled 20mf (5000v) cap to ground.
 
I've been told those oil filled caps rarely go bad and usually last longer than we do. Any clues where I should be looking to solve this hum problem? Of course it's not really noticible on SSB but I'm sure it's in there as well.
 
73 and thanks for any tips and patience with this !
John KX5JT

[K1JJ]

John,

The hum can also cause intermod on ssb by mixing with your audio.  We sometimes hear a faint, buzzy hum as someone talks.

Anyway, check the obvious first -  make up a HV voltage divider and put the scope on the bottom resistor to sample the AC ripple on the HV supply.  Also measure that 1uf cap, as it's used as a resonant circuit in the power supply to improve regulation. Also measure the 20 uf cap to be sure it's still good.

Check the diodes to be sure one is not open, giving a 1/2 wave supply.

There's not much else for supplies in a GG amp using 3-500Z's.  Any problem with the fil choke wud give 60hz hum.

Another test is to disconnect the Henry HV and connect up the SB-200's HV supply (or other known good supply) to see if the hum goes away.

Try this stuff and report back - we'll go from there.


T

[Mike/W8BAC]

Tom, Could you use a X10 high voltage probe meant for a VOM for this? Thinking about it, I don't see why not! I just smacked my forehead. An Ah Haa moment, THANKS!

Mike

[DMOD]

Hi John,

As you know I also have a 2k-4 and can't say I have had any problems.

In terms of metering, is it showing about 3,300 volts at idle, and about 3,000 volts on transmit?

Did the previous owner report any hum problems?

Are you sure your DX-60 is totally without hum on a quiet carrier? Try looking at it with a scope across a 50 ohm load. The GG amp WILL amplify anything put into it.

BTW, I have a 10kV DC/AC probe so if you need to borrow it, so let me know. You might be able to interface it with a scope (be careful) and see if there is any ripple on the B+ under load.

Phil - AC0OB

[ke7trp]

I am going to bet the Henry is amping the hum from the radio.  Once you get up to that kind of AM power, The Hum really gets amped up. 

Put the DX on a scope, Use headphones or a Spec an to try to hear or see the hum. I bet its there.

C

[K5UJ]

He said the hum is there no matter which rig he uses as an exciter.  Assuming he uses the exciters the same way with the Henry that he used them with the 200, the problem has to be in the 2K-4.

[ke7trp]

More power output makes the hum louder. Just a thought.

C

[KX5JT]

Okay I went over a few things and hums can be very deceiving.... looks like the DX-60 may be the culprit and the Henry is doing a fine job of amplifying it.  Maybe it's time to put a 3-prong ground plug on the DX-60! *embarrased grin*  

I'm seeing a very minute bit of ripple on the scope with the TS-570 but others aren't hearing it, it's way down compared to the DX-60.

John KX5JT

[ke7trp]

Dont feel bad.  I had the same problem here.  It is almost always the Radio before the amp.  The henry is a fine amp with a big oil can thats probably still 100%.

Hope you get it fixed!

[KX5JT]

So, when installing a 3-wire grounded plug, I understand I need to install the green wire (ground prong connected) to the chassis in such a way that there is strain relief and that it is longer so that it remains connected and therefore the chassis grounded in the event the cord gets pulled out it would be last to leave the transmitter.  

Are the two live wires position critical in anyway as far as they're connection to the primary of the transformer?  Does the white have to go to a certain side and the black to the other or does it not really matter?  I don't wanna fry myself or my radio.
 

[ke7trp]

It does not really matter on a tube radio with a Transformer like that.  Its a Primary winding that is continued back.   Does the stock plug have a wider lug on it? If so. This is the white wire.  The White goes to the larger side on the wall.  Ohm it out with your meter and just copy what is there.

If not, This means you can plug the stock plug in two ways.. and it does not matter.

In fact, now that I think about it.. Flip the plug around in the wall and see if the hum goes away.. I forgot that I used that trick many times on old gear.

When ever I replace cords, I plug it in and then check the case with a volt meter.  Hold the neg prong in your hand, Touch the red to the case.. Should see no voltage.  I had ONE reciever that had NO isolation transformer that bit me as some idiot wired it wrong.  So now, I just test em with a meter.  This is an old repair man trick used in AC and heating.. This has saved peoples lives.


C

[KX5JT]

Yeah, I remember the musicians I would hang with would check the chassis or mike and if they were getting zapped. they would flip the plug around.  Hmmm.... I'm not even going to sweat it, I'm just going to put the darn grounded cord/plug on the thing.

[ke7trp]

I used to repair and restore american 5 band radios like hallicrafters.  I would leave them running in the kitchen for testing. I found that many of them had hum and when you would flip the plug around, it would go away.  If you put the cord on it and the hum is still there, Its time to double up the filter caps.  Today, with good recievers and good antennas, People are real picky if they hear any hum.  Caps are so cheap its no big deal, unless its the Big oil cans I need for my T3!


C

[w3jn]

I have grounded the amp and the DX-60 via 10 gauge solid copper to an 8 gauge solid copper coming into the shack that's attached to the 8 foot copper clad steel ground rod right outside a couple feet away.
 

73 and thanks for any tips and patience with this !
John KX5JT

John, Gary W2INR had an almost identical problem with (I believe) the same amp.  Be careful; when he was messing with it he got across the B+ and got a nasty zap.

I think your problem is a ground loop.  You should NEVER depend on your RF ground to be the safety ground for the piece of equipment.  It *must* also be grounded to the service panel.  That means both the xmitter, and the amp.

Let's consider the fact that despite the fact you have a relatively close station ground, it will still have a considerable impedance at RF, and thus there will be an RF potential between the equipment and the station ground.  If this ground is also being used as the safety ground, any AC leakage (which there most certainly will be, especially if there are RF bypass caps on the input of the AC line), there will also be AC line current flowing to the station ground in the lack of a safety ground.   Consider also there will be an RF potential between the xmitter and the amp, and you have a recipe for a ground loop.

Use a star station grounding system - ie every piece of equipment has its own direct run to the station ground rather than using a bus.  And make sure all equipment has its own safety ground.  Last, your station ground *must* be bonded to your service entrance ground to maintain compliance with the NEC.  This means a separate outside conductor connecting the two.  The reason for this is that there will be considerable resistance between the two ground rods, which of course means there will be a voltage between them if current is flowing into both of them.

Now, the fact that the hum is 120 Hz could be that considerable RF is getting into the DX-60 and riding on the B+ somehow.  The fact that the hum level is "adjustable" via the RF output of the amp leads me to believe something like this is happening.

[K5UJ]

when you wire the modern power cord to the dx60 you got your three prongs on the plug.  You identified the ground prong already.  The wide blade (I am talking about the NEMA 120 v. American 3 prong plug) is your neutral return.  the narrower blade prong is your hot.   you got your three wires on the opposite end of the cord.  Put a lug on the ground and bolt it to the chassis.  Maybe there is a hole you can put a screw through with and bolt it down with a nut and star washer.  Otherwise drill.  The rear chassis power cord hole may have to be widened out with a drill and unibit or a ream.  Use a grommet or one of those plastic cord grips to hold it for strain relief.  Use an ohm meter to make sure you have the right wire for the right prong.  The hot wire should go to the lead that runs to your power switch which is probably going to a fuse and one side of the power supply tran. primary.  One of the stock power cord leads probably connects to it now.  The other side of the stock cord connects to the other side of your transformer winding.  That is your neutral return.  So you should hook the remaining cord wire to that.   These should be soldered.  There are probably lug strips that hold all these connections.

The idea of polarized power cords is so that the hot is always connected to the power switch first so there isn't 120 v. sitting all the way through the winding and fuse before getting to the switch.

I just remembered that with a three prong plug you probably don't have the wide and narrow blade, they are both narrow because the ground prong forces the correct orientation.   But your outlet will have the wide and narrow slots, so see how they line up.  The blade prong going into the outlet narrow slot is your hot.  Wire the DX60 accordingly.

Rob

[W4EWH]

... with a three prong plug you probably don't have the wide and narrow blade, they are both narrow because the ground prong forces the correct orientation.   But your outlet will have the wide and narrow slots, so see how they line up.  The blade prong going into the outlet narrow slot is your hot.  Wire the DX60 accordingly.

I suggest you buy an outlet tester: most hardware stores sell them, and your local electric supply house will always have them. A typical outlet tester has three LEDs in it, and they usually light up "Green" if the polarity of the outlet is good. It's worth checking, because there's no way to tell if that outlet was wired on a Tuesday or a Friday, and even Electricians are human.

These testers aren't 100% foolproof - you know what they say about "new and improved fools" - and what I found in my home was that the wire connecting many of the outlets to the panel was an early version of two conductor "Romex", i.e., it did not have a ground, even though we had three-prong outlets. The former owner had tied the outlet grounds to the cold-water pipes, which would make the home inspector's tester glow "green", but which is (according to my brother W3TDH, who is an electrician) an open casket just waiting for a body. (I can still remember him screaming from my cellar "Come and look at this!", about every three minutes after he started my "heavy up" job).

Suffice to say, if your home is old enough to lack a grounding system, it's a good idea to check the whole electrical installation.

HTH.

Bill, W1AC, who thought he was the only insomniac on the board

[KX5JT]

This is why I love AMfone!  I'm going to nail this puppy with help from this community.  

JN, Looks like I will have to get some more #8 or #10 and tie my station ground to the service round.  I think it's about 30 to 40 feet away.  I will do that at my earliest opportunity.  "Ground" is a confusing concept to many and I am no exception.  For instance, "RF ground" is not the same as "Ground Plane" as in the case of buried radials for a vertical.  Or is it?  In my case I run a balanced antenna (of the dipole variety) but I have a "station ground" which I always read I needed and it consists of an 8 foot copper clad steel rod right outside the shack wall.  #8 gauge solid copper coming into my shack and at this point, my amps, my dx-60, my antenna tuner all have runs from chassis ground bolts to the entry point.  I don't have each one going all the way out to the rod but they do each tie in as close as possible to it without leaving the shack.  Now from what I am understanding from you JN, I should also run a wire, in the most direct, pratical path between my service ground rod at the electrical box (in my case it's under the service box that is mounted on a wooden pole from which the mains are being fed from overhead at the street and xformer there).  


Rob.  Excellent information on replacing the 2 wire AC cord/plug with the 3 wire modern grounded type.  The original DX-60 that I have does NOT use a polarized 2-prong plug.  It instead uses a FUSE PLUG with 3 amp fuses behind EACH prong in the plug housing.  Each line then has a .01 mF with one side going to ground.  Then I can see that one line goes through the mode switch, which is a wafer with one position for OFF and other positions to operate different modes while ON.  That was a bad design.... I use a stomp to activate "extension cord" to power it up and leave the mode switch in AM position.  Although during retunes, I will have to move it to tune or cw before moving it back.   I may see if there's some place I can mount a 3 amp CB on the "hot" side (between the plug and the switch).  That's how the DX-60B schematic shows it was done.  Then I'll be sure that the larger hole is the "hot" side on the plug.

Bah! HUM bug!  I'm coming after you HUM!

John KX5JT

[KX5JT]

Good suggestion Bill!  I will add that to my list too. 

[N3DRB The Derb]

always make sure your black wire goes to the fuse. never run a fuse on your white (neutral) wire.  those 2 fuzed plugs are DEATH. Git rid of them.

and just get into the habit of using 3 wire grounded plugs & wire for every piece of gear in the shack. i got hit with a ampeg bass amp that still had it's 2 wire plug, when I touched something else that was rotated 180 degrees in the socket.

only has to happen once and you're a believer.

also really bad : grounding gear through your coax shield. run real grounds to your op desk. Grounding for DC and safety is not the same thing as RF grounding. 

this article attached discusses transmitter grounding from a broadcast perspective, a bit lengthy but it's the real deal.

[KX5JT]

DMOD Phil: "In terms of metering, is it showing about 3,300 volts at idle, and about 3,000 volts on transmit?"

Sorry I missed answering this.  Your suggestion to look at my DX-60 closer seemed to be the key! 

The meter is showing about 3400 volts idle and 3250 on TX.  I'm showing 242 volts AC at the outlet, a bit high I suppose.  I wonder about the filament voltage, if that is higher than 5 volts due to the high AC.

[KX5JT]

Okay, I have tamed the hum quite a bit now.  I took the DX-60 off of the power strip with some items including a "wall wart" from a mic preamp.  I moved it to another outlet by itself, although I'm fairly certain it is still on the same breaker circuit.  It's quite usable now but I am still going to follow through with the 3-prong and running a direct ground cable between station ground and service ground.  Things are looking up!

[K5UJ]

  Then I'll be sure that the larger hole is the "hot" side on the plug.

No, the wide blade hole is Neutral.  Go back and re-read what I wrote.  Bill's suggestion is a good one.  If you don't know who wired your house outlets you should make sure some yahoo didn't carelessly get the hot and neutral mixed up.  Like Bill I live in a boatanchor house.  Fortunately the shack was done with all new wire in conduit, subpanel, + outside ground at the service entrance.   

[KX5JT]

  Then I'll be sure that the larger hole is the "hot" side on the plug.

........you should make sure some yahoo didn't carelessly get the hot and neutral mixed up.

Lord knows I get it all mixed up... but then I'm not wiring homes.

Okay I was lied too! The hum that remains is definitely 60 cycle hum.  I went to http://en.wikipedia.org/wiki/Mains_hum and down the page there's an audio file with 60 cycle hum and I did an A/B comparison.  That's it!  It's not 120 hz.  Can't find an audio file with 120 hz but I know it would be an octave higher.

[KB2WIG]

 " I took the DX-60 off of the power strip '

FWIW, most of these things are crap.  Maybee OK for computer crap and other 'low' power apps. Some of the strips are good. Wiremold is an example of a fixed power strip. The older style metal strips, which look like the close spaced plasdic strips, with a switch, are nice also.

I home brew extension cords. Use 'handy boxes', good quality receptacles ( AKA straps), and 12 Ga. SJ or SJT cables. Mo expensive, but mo better.

klc

[K5UJ]

Here's a professional grade power strip surge supressor from price wheeler but it ain't cheap:

http://brickwall.thomasnet.com/item/standard-surge-protectors/ten-outlet-rackmount-modular-surge-protectors/pwrm15?&forward=1

you get what you pay for.