flyback cooling

[andy]

...

[N2IXK]

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....

[DaveWM]

Originally Posted by andy

Most RCA chassis have a high line voltage tap on the power transformer primary. This can help a lot with flyback temperature. Also, make sure your HV system is operating properly (check HOT current and shunt regulator current). The shunt regulator should see about 1mA on a black screen.

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.

[ctc17]

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.

[bgadow]

Originally Posted by ctc17

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.

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

[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.

[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...

[andy]

...

[DaveWM]

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.

[DaveWM]

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.

[DaveWM]

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