flyback cooling

[Findm-Keepm]

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,

[DaveWM]

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

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

[DaveWM]

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.

[old_coot88]

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.

[Phil Nelson]

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

[jr_tech]

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

[DaveWM]

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.

[Charlie]

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?

[DaveWM]

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.

[DaveWM]

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.

[DaveWM]

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....

[wkand]

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, 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!

[DaveWM]

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

[DaveWM]

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...

[wa2ise]

Originally Posted by DaveWM

being a man of science I think I see if I can zip tie on a thermistor to the fly on the core

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.