AM DA question

[stacker]

Replacing the rolling contact ($20) sure beats replacing a crunchy coil.

 

[WNTIRadio]

If you've had significant arcing between the coil and the rolling contact(s), you'll need to file down the rough spots on the coil and perhaps replace the rolling contact to avoid future arcing. At that point, you can use the DeOxit. Just use it sparingly. A little goes a long way.
DeOxit is the best product of it's kind that I've ever used. Far better than most "contact cleaners."

It's actually on the input to the coil, the roller is fine. But the whole thing is going to get a full cleaning, you can see the oxidation on it.

 

[WNTIRadio]

Here's the latest:

Cleaned everthing up with Deoxit, replaced a bolt holding the feeder onto the coil (the original one was charred). Dried and blew everything out, and now I can get tower #1 to come into parameters!

Of course, nothing is easy. As I get close with tower #1 (.115 +170) tower #3 does a literal 180, going from .420 +178.5 to .415 -177.0. As I move tower #1 away from where it should be, it snaps back to + phase.

At this point, should I send the monitor back to Potomac so I know for sure I'm not chasing my tail? However, the night pattern is spot on, and swapping out the sample lines to see if it's a bad module on the Potomac, it still is okay.

Sample lines look good, checked them from end to end this morning. No shorts, connectors are tight, no oxidation.

 

[Tom Wells]

Connectors are tight, but one or more somewhere have enough oxide or sulfide build up to cause high rf impendance.

Which is probably why as you come into proper parameters you got arcing right at the point where it was doing its work properly.

I bet one or more connections that seem beyond suspicion would test OK ohmically even if off-air but still act up this way.
Hope there's not too many, but I'd loosen and twist-polish the joints on almost everything in that tower 1 phasor cabinet that I could. Add Deoxit and twist some more, then retighten it all. May do nothing but at least eliminate these possibilites.
Where is this station located? How old is the equipment?

The can of Deoxit tell you that "working" the connector is an important step, and it is very true.
Just spraying it not of much use, friction is very important.

This reminds me of of a certain XTAL coplitts test osc I built with a roller coil... ramped smoothly on tuning when the coil
was clean but sort of wanted to "snap" to just above and below reasonance on the XTAL when the inductor roller wheel was tarnished.

 

[Doctor_Technical]

If I read this right, your tower #3 may only be doing a "literal 4.5", meaning it is simply increasing in relative phase from +178.5 to +179, then to +180 -- which is the same as -180, then to -179, etc.

Just means a bit more fiddling with the phase meter as you walk #3 back into adjustment across the +/- 180 degree point. Fully agree with suggestions to clean all contacts first.

 

[speakerman]

It usually works out just like cockroaches...if you see one you know there are others out of site. I would loosen-wiggle-retighten and clean all connections. That charred one has to be pretty bad to get to that point. I treated it as a preventative maintenance task. Its a hassle but always stabilized my system. You can slip Q-tips with Cramolin between the silver plated surfaces and follow with a clean tip often without pulling the hardware completely apart. Rubber gloves are quite useful if you have to work with a hot system. No fun working on a hot system...better if you can float the section.

The only other problems I had went away when I replaced all phase monitor lines with heliax. The connections to the sample current pickups would be worth checking also. Its summertime so not a freeze the fingers task.

It is possible the phase monitor could have problems although I seem to remember they used hermetically sealed relays which are very reliable.

Ground systems deteriorate also with time however those problems seem to show up more as the ground moisture levels change.

 

[stacker]

If I read this right, your tower #3 may only be doing a "literal 4.5", meaning it is simply increasing in relative phase from +178.5 to +179, then to +180 -- which is the same as -180, then to -179, etc.

Just means a bit more fiddling with the phase meter as you walk #3 back into adjustment across the +/- 180 degree point. Fully agree with suggestions to clean all contacts first.

Gotta agree with that assessment. You're on the right track.

 

[WNTIRadio]

Ahhh yes, the 180 flip point! In my frustration with it, my mind blanked on that. Duh! Okay, next time I'll slowly walk tower #3 back in.

Everything got a shot of Deoxit and loosened/tightened while I patched around the different parts of the phasor. Thank you to whomever put those quick disconnect switches in many moons ago.

 

[HadYourPhil]

And, if you send your monitor back to Potomac, get your wallet out... Expen$ive!!

 

[pstox]

I had a problem much like that several years ago, I do not know if it will help, but check to see if there is water in the isocoupler. The old Mosely gray Isocouplers were known for getting water in them, It is almost impossible to get water in the Kintronic.

I had the problem with water in the Mosely isocouplers before as well.

 

[WNTIRadio]

Well, got the DA into tolerance on all 3 towers today. Tuned up tower #1 and then slowly walked tower #3 into spec as well.

Left the room for about 10 minutes, and returned to that familiar smell of smoke. The same feeder originally mentioned had heated up and started to melt the bakelite holding the coil in place.

To review, I did/observed the following:

- Cleaned all connections with Dexoit.
- Loosened all connections and re-tightened them after wiping down the Deoxit.
- Cleaned the rollers on the coil with Deoxit and wiped off with a rag.
- Exercised all of the rollers with the Deoxit on them.
- Replaced the bolt holding the feeder to the ganged phasing coils with a new shiny one.
- Checked each tower for 50+j0, as well as the common point.
- Common point current jives with TPO.
- Tuning away from .115 +170 degrees to .115 +143 makes the heat go away.

Is the coil shot? Or is the bakelite that's holding it somehow breaking down. I really can't think of any other point where something is wrong. The night phasor tunes right up, all of the sampling lines are fine and the Potomac is in calibration.

Time for a new coil? Or is there a way to get new insulating substance in there and use the coil again.

Thank you to all for the help and suggestions in trying to narrow this problem down!

 

[speakerman]

Once bakelite starts to break down there is no turning back. Old tube amps had the same problem with instability when their bakelite circuit boards turned into resistors. The bias would often start drifting and take the circuit into melt down mode.

I would suspect some pretty high RF voltage at that bad connection. Fiberglas would be a better replacement for the bad bakelite. I'm no sure where to source what you need these days. I used to get stuff from Fair Radio Sales or Surplus Sales of Nebraska. Another possible source could be Max Gain Systems as they deal with a lot of high voltage RF components. http://www.mgs4u.com/index.html

 

[Koredump]

If I've read this correctly, the phase shifter is two coils ganged together. Sometimes the roller on one of the coils can loose contact with the coil. That will throw the phase off, but usually will cause a change in the ratio for the tower. You can check that by moving the crank a turn or so in either direction and see if anything changes. You will hear some arcing if that is the problem. Since you smelled something hot in the phasor, I would check the caps on both sides of the phase shift coils. Look for splits, or signs of something oozing through the body of the cap. A multimeter with a capacitance checker will tell you if the value has changed. Since you mentioned that a cap is feeding the phase shifter, that suggests a +90 network, so there may be a cap on the tower end of the shifters. Check that one also. My gut says you have a cap that changes value when it heats up.

That would be one of my first moves, also. Haul the old GR-1650 Z-bridge out of the van, and measure every one of those big mica RF caps on that tower's phase shift network and down at the ATU, while applying physical influence with a rubber hammer and some freeze spray. If you can get your hands on an OIB, and look at the tower's operating parameters while you tap around, you may locate a flakey component or connection that's causing your phase drift.

Good Luck!

 

[stacker]

Is the coil shot? Or is the bakelite that's holding it somehow breaking down. I really can't think of any other point where something is wrong. The night phasor tunes right up, all of the sampling lines are fine and the Potomac is in calibration.

Time for a new coil? Or is there a way to get new insulating substance in there and use the coil again.

I would suspect your coil is ok. If you think the bakelite insulator is breaking down, remove it and let the coil hang by the remaining supports till you determine if that is the cause of the smoke. If it is, replace it with a ceramic standoff. If that doesn't fix it....The heating at the coil input indicates that there is too much current at that point. You've cleaned up the contacts and they're tight, so you can take that off the table for now. You also mentioned that the night phasor works fine. Does it use the same tower and transmission line? If so, you can probably eliminate a transmission line problem. That really just leaves you with a cap changing value in the phasor as it heats under power, or an ATU problem (which could be a bad coil tap or a cap gone bad in the day ATU). If the ATU is tuned correctly, you should see your transmission line impedance if you insert an OIB between the phase shift network and the transmission line.

I've seen one instance where the input to a phase shift network got so hot that it actually burned through the bolt holding the connection together. In that case, there was a problem at the associated tower...a johnny ball at the tower had split, causing about 50 feet of guy wire to come into contact with the tower. Of course, that threw the tower impedance way off. Someone had cranked the phasor enough to get the correct readings on the monitor, however the mismatch between the phasor and tower was so great it eventually burned through the bolt.

Check the caps around the phase shift network. Check the caps at the ATU or anything at the tower that would cause a mis-match. Hope that helps. Good luck.