Flyback temperature

[Tubejunke]

Can someone please give a roundabout idea what temperature (in Farenheight) that an average 60s color set should produce when healthy. My set is the 64-65 Zenith, but I am making this separate thread and hoping that we can be non brand specific.

This way I hope future vintage radio & TV people will have a reference to what is an important and most often talked about topic. I have just never seen a specific temperature range for this. Certainly it will be a range due to the many variables involved, but it would be good to know more than if the wax is not melting off, or if it's not smoking then it's OK.

With today's myriad of cheap electronic devices to play with like a laser thermometer, it will be really easy to monitor this.

[Tubejunke]

Wow, I'm surprised at no feedback on this one! I saw a YouTube video once where the guy is checking his with a laser, but he never said what range of temps would be acceptable.

[Username1]

I think its more a measure of cathode current through the horizontal output tube that is important. If the current is right, the picture is the correct size, no yoke problems, then you can make a temperature measurement and that will be the temp. Also picture tube current should be correct.

Don't forget it's the current draw on the transformer that generates the heat......

And on the primary side it's the drive current through the winding.....

[Tubejunke]

OK, that helps since I have already been through the cathode current measurement and come out just a little above 200mA after installing a replacement for a broken horizontal efficiency coil.


Frankly I was a bit surprised at how little difference a lot of turns of the slug of that coil makes. I figured that in tweaking it I would see a vast difference, but not really that much.

[DaveWM]

It should make a big difference, have you checked the cap (or caps) across it? You should see a fairly sharp tune range (again with a subjective statement).

The prob with temp input is there are so many variables, ambient temp, line voltage, horz out emmisions, and then there is the lack of consistent measurement (kinda hot, slightly warm, barely warm,hot, very hot) so it becomes very subjective.

I generally use a LED targeted IR gun, aim for the hottest spot (often the point near the output lead to the HV rectifier).

I don't think polling peeps is going to get much good info due to all of the above.

That being said I personally think that if you were going to use a tube type tv with an RCA style fly, then active cooling would be in order as most of my RCA and clones get too hot for me to leave them running for hours on end.

a small muffin fan that moves the air around the fly makes a HUGE difference.
consider that the FLYs can not be easy to get AND they are 50+ years old make me think this is a good idea. And NEVER leave on unattended. The down side to a fan is IF they were to catch fire you would have a blow torch on your hands.

[Username1]

Dave is right that coil should have a peak, and if I remember right, you tune it for minimum cathode current.....
There should be a number in your manual....

[Electronic M]

I generally go by the bath water standard for flybacks if it's hotter than you want your bath water to be then odds are there is something that needs further work...If I plan to run a set all the time I do tend to try for cooler operation though.

Power supply transformers on the other hand are sometimes MEANT to get hotter.

[DaveWM]

fyi, I noticed you said you have a zenith, I am not positive on this, but IIRC a lot of those did not even have a eff coil. Zeniths seem to have a lot less issues with flyback. If you give me the chassis/model I can look at it.

[Tubejunke]

Originally Posted by DaveWM

It should make a big difference, have you checked the cap (or caps) across it?

I replaced the single cap across it when I installed it. I hope that I didn't connect it across the wrong lead. There were three and I wasn't working in the best light or position unfortunately. I would think that if I hooked up to the wrong lead that I would see some fairly major indication of it. I hope so anyway. Guess I'll get out the schematic and double check that.

[Tubejunke]

Originally Posted by DaveWM

fyi, I noticed you said you have a zenith, I am not positive on this, but IIRC a lot of those did not even have a eff coil. Zeniths seem to have a lot less issues with flyback. If you give me the chassis/model I can look at it.

Yes, it's a model 5111 and most certainly has the efficiency coil. It's stamped in the chassis and I have ordered and replaced it. Anyway, the Sam's folder that I have says that it is a 25LC30/U chassis. It's Sam's Set 722 Folder 4 if that helps. It will come in handy to see if I have the single cap hooked up wrong.

[Tubejunke]

Originally Posted by Username1

Dave is right that coil should have a peak, and if I remember right, you tune it for minimum cathode current.....
There should be a number in your manual....

Well, about 200mA seems to be the generally accepted in the realm of this vintage of color television from what I can tell. Now, what I don't know is about what kind of peak I should be seeing with this measurement. First I want to say that I am using a Simpson 260 and I use the 50 volt scale. So unless there is a big variation that I would see here a difference in say 100mA isn't going to look like a lot of deflection of the pointer.

To be specific, the lowest point which was around 200mA is as low as it goes and it doesn't go way high from there. Now I have noticed that the slope is pretty sharp in that it doesn't take much of a turn to make the difference. Really, this is probably a good thing as I wouldn't think that you would want the potential for some way high, possibly damaging amount of current to flow, and of course if it were way to low there would be other issues.

My thoughts of possibly botching the install of the .15mfd cap look to be wrong. The schematic shows (as well as the old unit I removed) the cap across the two outermost terminals, and it is. So the only thing I think that I could botch would be mixing the conductors up, so I checked to make sure that #2 terminal which is a center tap, was connected to a .1mfd which it is. The other two leads I think could be swapped and it wouldn't matter since they are both across the 1 ohm winding.

I have a good raster which is linear both vertically and horizontally. The only battle right now is the hissing of I guess corona arc inside the HV cage which causes interference in the picture. I just know that flys are very critical with these sets and being transformers we all know that we don't want them running too hot, so I thought that I would try to get an idea of a reasonable temperature and HOPING that the arc or whatnot is not somehow internal to the fly if that is even possible. I am not familiar with the symptoms of shorts or other conditions that may occur with flys.

[Tubejunke]

Still trying to get the corona arc out of this set and to make a long story short I changed the H. Output tube and damper. Then I hooked up my Simpson 260 to the cathode circuit and the set now initially holds about 200mA, but after several minutes builds up to about 250mA which I think is critical if not dangerous to the fly.

I should have just recapped this set, but I wanted to repair it first and see what I have, then consider a full or partial recap. Can someone advise me on what would cause this climb in cathode current and am I going to fry the flyback. It does seem to be running hotter, but not too hot to touch or anything. The darned brand new efficiency coil that seemed to be the only one in the country that I could buy seems to be frozen already! Can't understand that one. It was n.o.s. by Thordarson. I tried turning it from the rear and a chunk of the slug fell out. Geez!

Might have to sell this one to one of the "roundie" pros here!

[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.

[init4fun]

Originally Posted by Tubejunke

I should have just recapped this set, but I wanted to repair it first and see what I have, then consider a full or partial recap. Can someone advise me on what would cause this climb in cathode current and am I going to fry the flyback.

Hi Tubeguy ,

Any time I've encountered runaway cathode current , it has always been found to be either the grid circuit capacitors failing and driving the grid positive or a bad tube as old coot suggested . I've seen both gassy and tubes that have developed "secondary grid emission" do the runaway cathode current thing , but mostly find it in the capacitors slowly going partially shorted .

[old_coot88]

Originally Posted by init4fun

Hi Tubeguy ,

Any time I've encountered runaway cathode current , it has always been found to be either the grid circuit capacitors failing and driving the grid positive or a bad tube as old coot suggested . I've seen both gassy and tubes that have developed "secondary grid emission" do the runaway cathode current thing , but mostly find it in the capacitors slowly going partially shorted .

I was going with a gassy tube since he said it starts out normal at 200ma then climbs gradually. Whereas a leaky grid coupling cap woulda put the current high immediately.

But that cap should always be replaced as a matter of course anyway. Same goes for the grid coupling cap feeding any power stage (audio output, vert. output).