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#1
11-29-2012, 07:54 AM
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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... 
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#2
11-29-2012, 08:09 AM
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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... Last edited by DaveWM; 11-29-2012 at 08:25 AM.
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#6
11-29-2012, 12:53 PM
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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....
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#7
11-29-2012, 02:26 PM
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Quote:
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.
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#8
11-29-2012, 03:04 PM
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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.
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#11
11-29-2012, 05:20 PM
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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.
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#13
11-29-2012, 05:47 PM
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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.
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#14
11-29-2012, 06:24 PM
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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). Last edited by DaveWM; 11-29-2012 at 06:29 PM.
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#15
11-29-2012, 09:20 PM
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Quote:
__________________
Bryan
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