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 on: Today at 02:35:20 AM 
Started by SA2CLC - Last post by SA2CLC
Ok, It does work, but there is nowhere near the voltage swing required to drive the screens enough to get any useful power output.
By applying 275v to one of the screens, I get a steady 8w output. Measured peak-peak voltage at the screens driven by 6sn7 and a  1khz tone is around 54volts, so still a long way to go.
Tested a backwards 70v line transformer, managed to get around 90v pk-pk, driving it from a signal generator. Power out was about half a watt.

Might play with the anode resistors at the 6SN7s but there will not be enough swing whatever.

Transformer is the way to go Smiley

 on: Today at 12:23:17 AM 
Started by K1JJ - Last post by w8khk

Again, with no load on the street pole pig (everything in the house shut off) the sinewave is distorted as pictured. A heavy load does not effect it.

I guess we doubled, or I did not determine whether the frequency was in use before transmitting.   I must be one of those dreaded automatically controlled data station, providing internet service to the fishermen in the north Atlantic.....  my sincerest apologies, Hi Hi!!

If you are seeing the distortion on the incoming waveform, and you have no loads on the service, then there is likely nothing you can do within your premises to resolve the problem.  The power company must determine whether the distortion is on the 7KV feeder, or if it only exists on the output of your pole pig.  If it is on the feeder, they will need to do further research to resolve the issue.  If it is only on the load side of your transformer, perhaps a turn or two is shorted, and the transformer is already running hot.  A replacement pig, perhaps a more well-nourished pig, say 25 or 50 KVA, would be a welcome upgrade.   Do it for the children!

 on: Today at 12:16:35 AM 
Started by K1JJ - Last post by w8khk

But you gave me a good idea - I will bring the scope into the cellar tomorrow and close off the 200A breaker to the house.. completely dead.  And then look at  the sinewave connected only to the street pole pig.  I haven't actually done that yet.   Thanks.

The idea here is to look at what is coming into your panel WHILE THE POWER SUPPLY IS ON.
Then you will be able to see if the flat-topping is present on the line coming into the house.  If it is NOT present at the panel, but it is present at the input to your power supply in the shack, then the current peaks are causing voltage drop across the drop to your shack, and NOT in the feed from the utility. Then the simple fix is to upsize the feed to the shack, even if it is sufficient for the average current.  The peak current is only for a short duration of the 60 Hz waveform.

An example case in point:  Back in the late 80s, we had  large HP mainframe, running on 3-phase 208 power.  The computer had MANY switching power supplies, consisting of a capacitor input filter right after the bridge rectifier.  All the supplies demanded max current at the crest of the incoming 60Hz waveform.  Now, to make matters worse, each supply in the system was connected to neutral and one phase, 120 volt into each supply.  The load on the neutral was THREE TIMES the current on each of the individual phases.   The feed to the computer was four number 10, plus ground.  We looked at the signal on each phase, and the neutral, referenced to ground, with a distortion analyzer.  The power supplies were, in effect, current starved due to the excessive neutral current.  Later designs of the computer power supply used 208 volt phase-to-phase, and had inductance in series between the rectifier and main filter capacitor bank feeding the switching power supplies, problem resolved.  But the interim fix for the earlier 120 volt supplies demanding excessive peak neutral current was to upsize the neutral feed from number 10 to number 6, for a nominal 30 amp 208 volt three-phase service.   (Then later version did not even have a neutral.)

The point I am trying to make is that the "metered" current on your feed to your shack is probably well within the scope of the wire size, but if most of the current is in short duration pulses, then expect significant voltage drop over the wire sized for average current.  Kinda like the wiring in your RF tank, no?

So measure the waveform at the entrance panel, with the transmitter power supply loaded normally.  If it is clean there but not in the shack, then you either need to reduce the peak demands with power supply design changes, OR increase the peak current carrying capacity of the shack feeders to minimize the voltage drop at peak current, which causes the flat top waveform at the power supply input.

 on: Today at 12:08:23 AM 
Started by K1JJ - Last post by w4bfs
hi Tom .... when I used to work for TVA as an unlicensed nuclear plant operator (glorified valve ape) I used to study the 500kV step up transformers .... 1200 mvar single phase I think ... 3 used at a time and each tranny about 15 ft on a side .... the nameplate data indicated 3% harmonic distortion .... this made for interesting Tesla coil type effects in the switchyard like walking up to grounded panels in the yard and drawing 2" arcs to fingers with no pain ... most of the other workers were glad for me to take the switchyard job evolutions  Cheesy

 on: Yesterday at 11:34:06 PM 
Started by K1JJ - Last post by KL7OF

Tom I have had some chokes that made noise and others that were silent....I have mostly used what was available rather than what was correct ,but in true hammy fashion was always able to make things go...  Just seems like chokes (in the neg or pos line)  ..just make everything smoother..nothing empirical ...just my observatio....n...let me now what you find...I'm interested.

 on: Yesterday at 11:21:07 PM 
Started by K1JJ - Last post by K1JJ
Rick -

The regulation is great. I measured the 120-0-120 drop in the shack and under FULL load each leg drops from 120V to 119V.  It is very good regulation to the shack and from the pole pig. But it screams like crazy when doing it... :-).

Again, with no load on the street pole pig (everything in the house shut off) the sinewave is distorted as pictured. A heavy load does not effect it.

I am fishing for someone to tell me that I have excessive distortion and yes, it will cause loud xfmr buzzing...   Wink

But you gave me a good idea - I will bring the scope into the cellar tomorrow and close off the 200A breaker to the house.. completely dead.  And then look at  the sinewave connected only to the street pole pig.  I haven't actually done that yet.   Thanks.


 on: Yesterday at 11:17:43 PM 
Started by K1JJ - Last post by K1JJ
Thanks for the replies, Rick and Steve - this is encouraging.

Well, I got rid of the PS chokes cuz they just added to the noise. My thinking is if there is any saturation/flat topping/ harmonic-rich waveforms, all magnetic iron hardware is going to be affected.  It is quieter without any chokes for now.  That is a clue.

BTW, my AC line scope pics are taken with almost everything in the house shut off. I can't imagine the 15 KVA street pole pig being loaded down. And when I put on a full load in the hose, the waveform does not budge. That's why I think it is occurring BEFORE it even arrives to the street pole pig.

Interesting on you pole pig rating comments. I used to have a 5KVA up there until I complained about my arc welding pulling it down. But most of the houses around here still use 5KVA units.

Rick, do you think there is enuff distortion on my waveform to actually cause this problem?  I've never heard about this before and have not come across very specific info on the web. There is a lot of talk about harmonic distortion and power factors and how to correct it, but no one has actually said it will cause power supply iron to start buzzing like this.

Steve, on the scope hookup:  Just connect the AC neutral to the scope probe ground lead and the scope probe to the hot 120V line. (X10 probe)   Minimal load in these pics.

 on: Yesterday at 11:17:23 PM 
Started by K1JJ - Last post by w8khk
One more thought.  Have you looked at the line waveform at the main breaker panel, or only on the drop into the shack feeding the QRO supply?  You could easily look at it on a different circuit that is not loaded, while your power supply provides the load on the shack drop.

If it is clean at the panel, and flat-topped in the shack, perhaps a larger wire circuit to the shack would be the simplest fix?  And again, it is not about sizing the wire for the average load, but up-sizing the wire to avoid the voltage drop on current peaks.  Standard size wire for the load current plus long distance from the panel to the shack may also contribute to the problem.

For my larger 120 volt loads, for example the Hallicrafters HT-32 linear, which runs at 120 volts, I use a 240 to 120 isolation transformer to cut the line drop in half.  You may be suffering the same issue with your 240 volt load.

 on: Yesterday at 11:05:55 PM 
Started by K1JJ - Last post by KL7OF
Tom..  Do you have any chokes filtering your supplies?   Or just Brute force capacitance?...curious as I am starting to figure my line supply as part of the system....I really haven't had to think much about it before...I will try to post some scope shots when I get the setup going..What is your setup for the scope patterns you posted? Are those loaded line patterns ? with the big rig on?
 Gud Luk..Steve

 on: Yesterday at 11:00:23 PM 
Started by K1JJ - Last post by w8khk
Tom, a 15 KVA transformer seems rather small, even if for only one home.  That provides only around 60 amperes at 240 volts. 

In my neighborhood, most homes have 150 to 200 amp service at 240 volts.  In my case, the pole transformer is 75 KVA, shared by three homes.  75 KVA is about 312 amperes at 240 volts; if equally loaded by the three homes, 104 amperes per home.  This allows for much higher peak load without flat-topping, and the peak loads are usually not simultaneous across the three homes.

I realize in normal use you would not reach this much load, but with air conditioners, water pumps, water heaters, etc. it seems 60 amperes is rather PW.

When you run a choke input power supply, most of the load on the service is just on the voltage peaks, when the rectified AC peak is just above the voltage charge on the filter capacitor.  Using choke input, with the additional filtering of the series inductor, spreads this load period over more of the input waveform.  The more inductance, the less peak current for a given average current.  I realize you can reach a point of diminishing returns, and the resistive losses in the inductor add to the problem.  But that is probably the only thing you can do, other than requesting a QRO upgrade to the pole transformer.

You could also offer to reduce the cost of the upgrade by volunteering to handle the recycling of the PW pole transformer now in service.  You might also mention that the flat-topping and power factor issue might be alleviated with an upgrade, thus avoiding a pole transformer crap-out in the future during one of your January old-buzzard shack-heater transmissions!

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