Flyback temperature

[Tubejunke]

Originally Posted by old_coot88

Aw jeez that is a bummer. Coupla questions..

Did you still get the initial 200ma reading after the eff. coil slug broke?

When the K current climbs to 250ma, what does the raster look like?

Gassy H output tube could be the cause of excessive current (since it starts out normal, then climbs).
Definitely don't run it like that, since it's hard on the fly.

OK, I am going to try to answer all questions based on this initial quote. I did get about the same readings after the slug broke. Just a chunk fell out of the back side under the chassis. The raster to me seems fine, but remember all along I have had barkhousen lines or some horizontal interference along with the distortions of the corona arching which I could never pinpoint, but sounds like it is inside of the HV rectifier. Oddly, when I did this check I had the polarity wrong on the meter, so I switched it to -DC. That was a mistake; probably a dumb one. The movement went the right way, but I did get a bit of a smell of something burning. Switched the wires, went to +DC and the arching was gone; just the runaway current....

I did save the old slug from the coil with the broken spool, but I can't get the new one to move at all and I fear it falling into a bunch of pieces and then finding out that the old slug is a different size of something. I don't know why that thing froze that fast except for possibly the coating on the windings heating up and gluing it in place. This set is driving me crazy....

[Electronic M]

I once brok a slug because I was being an idiot and using a metal hex key (BIG nono ) instead of a plastic diddle stick. Slugs can be replaced with ones of similar dimensions from other parts coils/sets as long as the threads of the inductor are not shot. It might be a good idea to look into a plastic safe lubricant for them...

EDIT:One thing that might loosen your slug is (provided the wire is thick enough to stand the current) with the set turned off connect a D cell battery across the coil and let it warm up until the slug loosens up, then remove the battery and the slug and then quickly try to clean any wax or other gunk from the slug and coil threads before it cools....IIRC I did that to free the frozen lin. slug on my CTC4.

[Tubejunke]

I may have to try that. The coil has three terminals as it is center tapped. I hate to, but I assume that I would connect the D cell to the outside terminals. Makes sense I suppose. If my old original slug is the same dimension as the Thordarson "direct" replacement then I am in business.

However, I tried adjusting after the current went high, so there may not be a reason to further try to turn the slug that was dipped to 200mA to begin with. Perhaps, and worse case scenario I will be able to find someone with a spare Zenith chassis that would sell me one, but I had zero luck with that before. Maybe this is why everyone has RCAs. Stick with what everyone has so you have resources for parts. I like Zenith and it's really amazing that the set works to the degree that it does being that old and dormant for several decades.

[Electronic M]

There are plenty of folks on this forum that have one or more Zenith roundys (my self included). The reason you don't see a ton of repair threads on Zeniths is that they are a lot more stable once working than RCA based sets (I also own some RCA based sets, and can tell you that the PCBs are a perpetual source of intermittents)....Heck a number of Zeniths that I own are still going on all original parts save for tube replacements.

[Tubejunke]

Yeah, they are supposed to be really great sets, as you said once working. I'm going to try to keep fighting that battle. I wish I could get that slug to move just one more time and slide the old one in there. Seems like they would be the same size one being a replacement part.

The thing was free as a bird just a few months ago. It doesn't seem to run hot, but does look like it has at some point as there is what looks like melted laminant that has run what would be down if the set were sitting upright, but it has been on it's side since I put that thing in. I'd give every N.O.S. vintage flyback and yoke I have for a couple of extra coils and maybe a spare fly just in case.

[Tubejunke]

Originally Posted by Electronic M

EDIT:One thing that might loosen your slug is (provided the wire is thick enough to stand the current) with the set turned off connect a D cell battery across the coil and let it warm up until the slug loosens up, then remove the battery and the slug and then quickly try to clean any wax or other gunk from the slug and coil threads before it cools...

I still may try this as I would like an intact slug in my new coil, but the other half of me says leave it alone; for now at least. I have actually ended up with some better results then where I was heading earlier. I thoroughly cleaned the cup that the HV rectifier sits in and eliminated (for now at least) the corona arc and resultant interference that it presents to the raster.

Also, I took out the regulator tube that I had put in the night I checked the cathode current as well as the H.O. tube and put back what had been in there before. I didn't really have a reason to change the H.O. tube other than to try to get rid of the barkhausen interference lines ever present on both sides of the raster. Most prominent on the right side which I think is covered more by the damper tube. I may be wrong in these statements and welcome correction. I say barkhausen lines meaning a light line that once was straight but now is twisted like a snake. Sort of like the horizontal hold is about to let go although it is stable.

The regulator tube was just one of two that I had that tested better on emissions and no gas. However, when I pulled it I noticed that there is a sort of a ring that you see on I believe the would be the plate or the upper portion. The dark coloring of that ring is gone and is copper colored as if some arching has gone on in whatever set it came out of. It is not from use in my set. I just picked it up in a box of tubes at the flea market. Even though this tube had a better emission, it has a shorter life test on my Hickok 6000A. At any rate my H.O. cathode current stayed around 200mA as long as I ran the set as opposed to the runaway current that I mentioned previously. I still don't know how it will perform over a long period of time, but I will find out and post.

Again, the coil would naturally be better intact and able to be dipped, but I certainly don't want to further damage it as I have absolutely no leads on another. I don't see why they are so hard to find; at least second hand. As far as heating it up with a battery goes I am afraid that I may short the windings by burning away the laminate. At least I had adjusted it before it froze up and being new I fear that the only way that it could freeze up was that it was somehow overheated and the insulation that melted is holding it in place. As long as it isn't shorted I am ok and I have the spec sheet resistance values.

Thanks so much for the tips everyone!

[drussell]

Originally Posted by Electronic M

One thing that might loosen your slug is (provided the wire is thick enough to stand the current) with the set turned off connect a D cell battery across the coil and let it warm up until the slug loosens up, then remove the battery and the slug and then quickly try to clean any wax or other gunk from the slug and coil threads before it cools.....

Originally Posted by Tubejunke

I still may try this as I would like an intact slug in my new coil, but the other half of me says leave it alone; for now at least.
...
As far as heating it up with a battery goes I am afraid that I may short the windings by burning away the laminate. At least I had adjusted it before it froze up and being new I fear that the only way that it could freeze up was that it was somehow overheated and the insulation that melted is holding it in place. As long as it isn't shorted I am ok and I have the spec sheet resistance values.

Can't you just lightly warm it up with a hair drier or heat gun wafted around the area or something so it's less likely to harm a winding trying to use it as a heating element?

[Tubejunke]

Originally Posted by drussell

Can't you just lightly warm it up with a hair drier or heat gun wafted around the area or something so it's less likely to harm a winding trying to use it as a heating element?

That is exactly what I was thinking. If a hair dryer will do it, that would be the thing to use. A heat gun puts out an incredible amount of heat and I fear that it would melt the spool which takes me all the way back to my original hunt for one of these. My spool had deteriorated to dust and the winding was just dangling. That may have been OK really as the slug was in there and the bulk of the winding was just as it would be with the spool, but the dangling winding's weight caused some separation of the winding and I was advised that just that would be enough to render the part bad.

I should have (back then) checked the H.O. cathode current while moving the winding around a bit to see what it would do.

[old_coot88]

OOPs! Duplicate post.

[old_coot88]

If the K current is holding reliably at 200ma., i would be inclined to not fuss with the eff. coil any more (despite not having been able to find the 'dip' earlier).
Back in the day, 210ma. when 'on dip' was considered nominal.
200 would have been all the better.

[Tubejunke]

Thanks and I am inclined to think the same as (correct me if wrong) if the set is holding for let's say 30min. at 200 or 210mA and then I once again see a rise, it's not going to be the coil causing the rise and adjustment would not rectify the problem. I hope my thinking is right on this. That way I can move on to getting the video back to being clear and the color working once again.

I get so frustrated because at first this set played so beautifully and then the bottom fell out. First loss of color which has reemerged a time or two, followed by a pretty nasty picture. I'll have to post some pics I took of it playing the Woodstock movie. I WILL get it back to that state; 'with a little help from my friends.'

[old_coot88]

Originally Posted by Tubejunke

Thanks and I am inclined to think the same as (correct me if wrong) if the set is holding for let's say 30min. at 200 or 210mA and then I once again see a rise, it's not going to be the coil causing the rise and adjustment would not rectify the problem. I hope my thinking is right on this.

I would agree with that approach.
In addition, i would consider putting a #44 bulb in series with the plate of the H out tube. It's rated at 250 ma at full brilliance, so it'll run a little dimmer and oranger at 200 ma. Thus any brightening will give a visual alert of current rise.
Either that or keep a milliameter in the cathode leg.

[Tubejunke]

Originally Posted by old_coot88

Either that or keep a milliameter in the cathode leg.

With that thought in mind, or perhaps fusing the circuit; I simply broke the cathode leg and soldered in two strands of wire long enough to reach well outside the chassis. So far I have no permanent mounting and not sure what I will do there. No big deal, but it is really convenient to be able to wire in my Simpson 260 for these checks. When I'm done I just throw on a wire nut and go about my business.
I used stranded wire as that is what I had on hand. I think in the present case of the wires moving around a bit and for future routing purposes that stranded was the right decision.

I hadn't thought of using a bulb really. Sounds like a good idea if you know the nature of the bulb meaning what it would look like at it's brightest lumination and 'normal'. It would look a bit raggedy, but you could simply have it dangling under the set to be observed while watching the set. For that matter I guess you could put it in the tuner indicator! LOL

[old_coot88]

For comparison, the bulb's 'normal' is at its rated 6.3V (/ 250ma.).

The bulb would need to be located physically at the plate cap, because there's several thousand volts of pulse there. Running wires around would introduce an arcing hazard.

The alternative would be the cathode leg since there's no arcing hazard and you can run wires around with no problem.
But in the K leg, the bulb will introduce a few volts of negative grid bias plus a bit of negative signal feedback. This will reduce the gain a bit, which may or may not be a problem.
The feedback can be cut by bypassing the bulb with an electrolytic (maybe 1000 uf @ 10V.).

Of course a milliameter in the K leg would be ideal since it's essentially a short and would need no bypassing.

[Tubejunke]

Mr. Coot, I must stop for a moment here and say thanks so much for reading into what is only limited information and trying to help someone sort out a situation like this. I am often amazed at the amazing amount of information retained and conveyed through people like you who I can only assume must have been lucky enough to work in the electronics field when it was what I refer to as real electronics.

As a student of the discipline myself I have often felt cut short by what has in many ways become a dumbed down craft both in education and in "the field." A lot of it has to do with the throw away society that we have evolved into that simply leaves no place to exercise the kind of knowledge that was once almost commonplace. I could go on and on in a rant here, but I work every day around "techs" who can't even read an analog meter. If they understood what they are looking at, they wouldn't understand how to use multipliers. There are those who by the grace of God know AC from DC, but really just the terms more than what they really are based on electron theory along with the fairly rudimentary understanding of the sinusoidal wave and how it can be altered to create the later. They don't have a need to know for one thing I guess to give them credit. It truly is a plug and play world now and I can't say enough in thanks to those who help pass the torch of what could become a lost art. Certainly, were a long way from vintage color TVs and such, but I truly believe that it takes a vast understanding of electronics to be successful at doing what we do here at VK and other places like it. I think the common Radio and TV repairman of yesteryear would bear the same or more knowledge than that of someone with a graduate degree these days.