flyback cooling
 

My recently replaced flyback in a CTC-12 gets pretty warm, like 150f after about 45 min running, it looked like a NOS fly, dripped out quite a bit of wax. I have read in old service manuals that it is not uncommon, and indeed most of the sets I find that have OEM flys do indeed have a moderate to large amount of wax loss. I have checked out the HV and it all seems well (correct HOT cathode current and screen voltages, regulation current, HV setting).

I was considering installaing a small muffin fan on set. I would do this by fabricating a new top for the HV cage, with a small (1" to 2") fan blowing down and a vent hole next to it to allow the air to escape. would add a thin non conductive divider to act as a plenum down to the fly to make sure the air path is not short circuited. I have seen many sets that just have the HV cage removed, perhaps to aid cooling?

I realize the down side is the large volume of air will result in a large volume of dust, if that is the case maybe a airfilter on the intake side. I don't think I will be using it frequently enough to clog the filter, I would just like to watch a 2 hour movie and not be fretting of a too hot flyback.

oh and ROLL TIDE...

some more ideas, thin cardboard formed duct (like a tube from a paper towel roll), down the side of the cage, open up to a shroud around the fly. Fan mounted inside the tube. Reason for the fan in tube is to try and better muffle the sound of it running which has been my main reason for not using them in the past. Two exit holes on the top part of the cage that swings over the top. I suppose to be safe I should put a metal cap over the hole (spaced to allow air to escape) as an X-ray stopper although I highly doubt X-rays would be a problem.

I have discussed the issue of Flyback heat with another member of this forum, unsure of exactly what is causing the heat, since a lot of it seems to be in the HV tire, also since I am sure the insulation on the wire is fine at these temps, there may not be a problem even with massive wax loss other than the mess and perhaps the loosening of the mounting of the fly tire itself to the frame.

I am guessing here that the HV at say 25kv and 1-2ma avg about 35watts some of that will go to heat in the tire...

With the 6BK4 and the focus rectifier inside a small enclosed cage doesn't help the situation either...

Yea the shunt tube does make some heat as well, all inside a sealed up metal box, and ALL of its shunting goes to making heat, as well as the filament.

...

My biggest worry about forced-air cooling an HV cage would be dust. If you ever looked inside a computer case that has been run for a few years, there is an amazing amount of dust that coats the internals, even when operated in a "clean" environment.

At least in a PC, the dust just impedes proper heat dissipation. Inside an HV cage, it will cause leakage currents and eventual arcing, with a possible fire hazard.

If you want to go this route, I would suggest using the fan to pressurize the cage (rather than sucking warm air out), and fit a proper dust filter on the inlet side of the fan. Then, of course, you need to remember to change or clean the filter occasionally....

I am on the 128v tap now, that reduced the HOT current some. Its at about 198ma shunt it about .8-1ma, HV is about 23kv.

control grid of the HO tube is -47 with with a vtvm, screen is 140v grid drive is 200v PP with the correct form, replaced the .01 coupling cap, adj the eff coil for max dip.

Diff 6DQ5's were used there where minor changes in both current and screen voltage, I settled on the one with the lowest cahode current and screen voltage.

How about a small liquid cooling system with a heat exchanger on the back with a fan? You could use plastic tubing that wouldnt conduct the hv.

Having a fan blowing directly on the flyback would blow stray electrons throughout the room and cause x-rays to collect on the nails in the walls.

Or how about this....stick one of those slant flys in there that work in just about everything and see if it gets as hot.

...

interesting I ran it with the back of the cage off for nearly 1 hr and it was just warm. Oh well maybe that is the answer for now. I will try it again and see how it goes.

perhaps it just needs some natural convective cooling a good sized opening on the bottom and the top right over the shunt with some spaced off caps I just hate the idea of cutting up the cage.

Duh make one, I have some scrap metal and its a very simple part to make.

a quick shot on the fly after about 30min 125 was the hottest spot, the shunt was about 310f

for you fluid dynamics types, I assume a smaller opening on the bottom near the base and a larger opening on the top would work best? I am thinking of about a 2" round opening near the base and a 3" opening on the top.

after 1 hr it was at 140f, too hot for me, so I placed a 3" 12v fan on a 9v battery right at the base, within minutes it was down to 100f so looks like I will stick with forced air cooling. I have some other sets that have much harder to come by flys that will also get the treatment.

5 more min and its down to the low 90's wow...

will be interesting to see it spike when I turn off the set (and remove the power from the fan).

This might be good information for the investigation into why certain 60s GE color sets would explode, along with the nails being sucked out of the wall. (see the old, old thread) Must've been real good airflow in those sets, good updraft, maybe? Low-budget particle accelerator. The guys out there working on clandestine fusion machines, or whatever they are, might be very interested in this. I am mostly joking :)

Dave,

Before doing any mods, take a look at RCA's patent for the CTC12 HV cage - there are MANY safety concerns in the design of the enclosure. The US patent is 3273021.

Aside from what has already been proposed, I'd use a solid state HV rectifier, and make sure the regulator was a 6BK4C, not a 6BK4 or 6BK4A. The 6BK4 was the worst of the regulator tube designs - RCA pulled all of them when they brought out the 6BK4A (actually a Sylvania design, improved upon by RCA). The 6BK4C/6EL4A employs all of the improvements. It seems RCA, in an effort to improve the 6BK4's reliabilty, punched holes in the anode to help in outgassing of the tube at manufacture. The holes allowed the escape of X-radiation, so they inserted some baffles to mitigate the X-radiation (6BK4A) and later added both the denser (leaded) glass envelope and improved anode to further deal with the X-radiation threat that exists when the regulator tube is operated even marginally out of it's normal parameters (25KV, 1 to 1.3mA).

Hope this helps in some way,

http://www.google.com/patents?id=lq9...page&q&f=false

interesting reading. looks like adding forced air cooling IF the flyback were to catch fire would just create a blow torch out of it :yes:

I still like the idea of the cooling air flow, but will def look into the late model shunt.

after reading up on that patent, I decided to try another experiment. this time I have some thick cardboard slid in between the shunt and the fly. I had noticed in the past that the top part of the fly was the hottest, which also happens to be closest to the shunt. Perhaps radiant heating is in play, so will see if this helps. The patent shows separation between the shunt and its own cooling slots away from the fly, keeping the fly in a sealed fire proof box.

Adding combustable material into an area with potential for a high voltage RF arc is a bad idea. It can start a bonfire in a heartbeat.

Finally, a good use for all of those asbestos heat shields that people pull out of old radios and throw away :)

A shield redirects heat, but doesn't make it go away. Unless it directs heat out a ventilation opening, I wonder if it would make a significant difference inside a sealed box, once the system reaches full operating temperature.

Phil Nelson

Well, there are 3 different ways to transfer heat; radiation, conduction and convection. Why not use all three?
1. Paint the inside of the box black to absorb the heat *radiated* from the tubes/flyback.
2. The heat would be *conducted* through the metal to the outside surface.
3. Mount cooling fins on the outside of the box so that natural or fan-induced *convection* can carry the heat away.

jr

the cardboard did not help much so I stopped when it hit 125f. So I am back to the active cooling idea. I plan to hit the surplus joint and buy some sheet metal prob copper or alum since its easy to work, and check out the different fans.

That was indeed an interesting read about the cage design. Makes one realize there was a hell of a lot more thought put into design than one might think at first!

Dave... curious... did you happen to compare temperatures with other chassis using wax flys?

They seem to be all over the place, but most run hotter than I like. I have never had one that was under 100f after a long run like 1 hour or more.

I just got back from the surplus store. here is what I cobbled together, starting with some 1.5" ID foam pipe (used for insulation) I taped the seam, then using a soldering gun I melted out a square shape at the top so the square muffin would sit down into the pipe, the ID of the fan was about the same for a smooth transistion thru the duct. this is the top the fan will sit outside the fan cage. near the bottom of the pipe I cut a rounded slot that fits loosely over the tire, with enough room to allow the air to come out and flow over the tire. On the bottom I fashioned a foam plug that seals the bottom and conforms to the same cut out. With hindsight would have just fille it with some foam and then used the solder gun to cut the slot on the bottom, but it should work well enough to see if the idea has any merit.

I have the fan running on a 9v battery (12vdc rated fan), its much smaller and less air than the larger muffin that I was using before, but will see if it works or not soon Oz is on now will run for about 30 min and check.

this requres no mods to the cage but for a new top with a hole cut in it for the pipe and an outlet hole. since the top is swung open completly right now I will test it again with the fan/pipe out and the top wide open to see how much is fan and how much is just the open top.

I did buy some copper sheet as well to fashion a new top JIC it this works out. I really need to incorporate a couple slight bends to make it fit better as the flanges of the cage made it a bit of a tight fit coming out, but that should be an easy fix.

being a man of science I think I see if I can zip tie on a thermistor to the fly on the core and take some resistance over time measurement to see if I can get a better feel for what works best.

If that does not work then she is a witch, burn her....

Flyback/6BK4 Cooling
 

DaveM said: "will be interesting to see it spike when I turn off the set (and remove the power from the fan)."

Now that you are designing cooling systems, :D you need a 555 timer, a relay, thermistor, and a constant 12v power source to keep the fan running after the set is turned off until the fly cools. I'm kidding of course!

I was just going to use a 2000uf filter cap...JK

120f after 45 min with fan and duct tube

running test with no fan but top open

Watching THE game during the test.. roll tide...

Just be careful that the horizontal flyback pulse doesn't couple into the thermister leads, else the ohmmeter may get confused. And also don't create a sneak path for high voltage static discharge if you connect the DVM to it, there's a risk the meter may get zapped.

dont think I will bother with the thermistor, the experiment has proven to me the only way to really keep it under 100f is a 3" muffin right at the base. I will prob just figure a way to mount it there and leave the cage off. I am not worried about fire as I never leave it running unattended, and I assume the x rays if any are still going to be shielded by the reaming 1/2 of the cage which effectively blocks the front (where I will be viewing).

While a 12 flybeck is not that hard to comeby my CTC-5 and CTC-9 are a bit harder. I was hoping to learn about best ways to add active cooling on this set but the real target are those.

I may get motivated and build a cage with the bottom cut out for the larger fan.

I used some very thin copper clad (both sided) material to fab up the cage. It was very easy as the material would bend sharply and you can burnish in a nice 90 degree bend. holes and cut outs are easy with some curved small scissors.

I folded in the tops about 1/2 inch and lap seamed with solder to hold its shape.

I still need to fab up a top, but will wait on that until I test it out.

cut a large round opening that puts the fan right at the side of the fly, used some silicone dabs in the corner of the fan to hold it in place, spaced up the fan just a bit from the copper (I am hoping that will keep the vibes from the fan from being amplified by the thin copper).

I will take some pics tomorrow after the silicone has a chance to setup. I only have about 1 hr total fab time into it so if it does not work its no big loss.

I will still have to make up a DC power supply, I think the filaments would be fine with a 1/2 wave and a 100uf filter cap.

I could not wait, the silicone had set up enough to hold the fan so I installed the cage and hooked up a 9v battery.

Its very quiet

when the HV comes up the fan slows down, perhaps the fly is effecting it, like when the neon bulb lights up near the tire.

the air is restricted by the close fitting back, I can put some spacers on the cage that should keep at least some clearance for air to get by, but its not ideal, and there is no real good way to mount it as one side sits next the horz out tube, one side is against the side wall and one side is on the back. I may have worked better if I just mounted it on top and aimed it down but I liked having the fan right up near the fly.

ok not gonna work, I had some arcing from the fly to the fan, that can't be good and the fan does slow down a LOT that close the the tire.

so its back to mounting the fan on the top and just letting it blow down. so will try that again.

That would certainly slow me down!! :yes:

yea you could hear the fan slow to about 1/2 speed as the HV came up, yikes.

I think keeping the orig cover with the top off and a sheet of mylar to guide the air downward may work as well. Other sets with more room would prob work fine, like my CTC-5 which has the top of the cage that can be removed and has plenty of space for a fan.

one more try , this time with the fan on the outside of the box, far enough away from the fly to not slow down, but it would be completely outside the back of the set which would mean I would need to cut a square hole in the masonite back, not going to happen...


but it sure works well, been on for over 1 hr and its about 95f, and does not seem to be getting any hotter, I suspect I could run it all day and thats as hot as it would get.

So one more try this time I will try side mounting 3 of the little fans along the side by the HO tube. Since they are small I am pretty sure they will fit there, so I will have a 1" wide by 3" tall hole on the side.

I think I got it worked out.

I cut a third hole this time on the fly cage side next to the side of the cabinet, I can stack two of the mini fans in there and get them pointed right at the flyback, about 1" away from the tire. the fans suck air thru a very tight dead space, but there is at least a 3/4 inch space so they are not starved off and the back can go back on.

The down side is the fans are very noisy so I will have to see if I can do anything about that. I would love to get the 3" fan back on the side I just dont think I can get it to fit and still be able to install the cage.

Mentioned at the start of the thread - running sets without the HV cage. If this did help cooling a bunch, is it a good idea other than that? I was thinking it might be asking for trouble if a wire elsewhere in the set happened to stray over there while it was running, though precautions could be taken in that case. Other than that there is the basic safety factor of some kid sticking a screwdriver thru the back or whatever. Also would lack of the cage make arcing less of an issue, since then there wouldn't be a cage there for arcs to jump to?

Also mentioned was using a solid state HV rectifier. I still do that in some of my color sets (not my b/w sets), but have heard scary things about them possibly shorting and then taking the flyback out along with them. I have left them in though. I also use the little solid state focus rectifier substitutes and worry less about those since the voltage is only 1/3 of the ultor voltage. I simply like the idea of taking those two filament loads off the flyback so it doesn't get as hot in the first place regardless of cooling methods, but I guess if one of the SS plugins ever does kill one of my flybacks I'll change my mind. : )

I've thought about adding fans and such but as noted, I would definitely worry about that bringing in lots more extra dust. In the long run, I run my sets infrequently enough and for such short periods when I do, I'm not really worried about the flyback getting any more melted than when I got the set, nor about those SS diodes shorting out.