[Amps] tank coil heating

[Will Matney]

Chuck,

If the tank coil is copper tubing I come up with a way of cooling them if you have a pressureized chassis by a blower. What you do is take a piece of teflon rod or something similar that's RF safe, and drill a hole through the middle the same diameter as the tubings O.D.. In one end you push in the end of the coil or the tubing into the hole, and use a small set screw in a tapped hole in the side to hold it in. A person could glue it in with epoxy also, just don't plug up the tubing. The botton of the rod goes through the chassis and is held in place by two nuts, one on either side of the chassis making a it a standoff. For this, the other end of the rod needs to be threaded. You can use a piece of 3/4" O.D. teflon rod to make this where a regular die can be used to cut 3/4-10 threads. You want to use thin nuts here to mount it with, plastic if possible. The other end of the coil where it meets the high frequency end towards 10 meters needs to remain open (not blocking the inside of the tubing where air can flow through the tubing). Essentially, the pressureized air from under the chassis comes up through the teflon standoff and enters one end of the coil / tubing, flows through it, and out the other end thus cooling the coil.

Another way I seen in large commercial amps is to come up out of the top of the chassis with a piece of tubing around 1/2" + O.D. to where it's vertical height comes out just under the center line of the coil. On top of the tubing, they put a 90 degree elbow on it and aim it at the coil. The end of the elbow should come out about the center line of the coil. The pressureized air comes up through the tubing and is blown across the coil when it comes out the end of the elbow. I seen them use copper tubing/pipe in one, but that might not be a good idea around a tank circuit over stray C and L. Plastic pipe like PVC would probably work. They were doing this to cool the finned anode connectors on top of the tubes.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 5/10/06 at 7:54 PM Partain, Chuck wrote:

>I'll go peruse the archives again but I'm going to post this here anyway.
>I noticed while on 20m tonight running about a kw that the tank coil was
>getting 
>HOT, one of the wires connected to it (the 20m section) was turning a nice
>shade
>of darker! the coil is warm.
> 
>also When I pulled the cover (I was looking to see where all the hot smell
>was comming from)
>I noticed that a doorknob cap I have installed next to the load vacuum cap
>was also warm!
>i'm using that cap to get me on 80m its in parallel with the 1000pf vacuum
>cap
> 
>everyone I talk to with it said they notice NO noticible difference when
>its on or off only
>a few s units higher! (no audible distortion)
> 
>the cap I am using is labelled n4700   591m 30kv  706h and has a c with an
>m inside of it.
> 
>are these suitable for what I am doing? hell, its 30kv! why warm? what
>should I be looking for?
>the amp seems to load up pretty good into the vertical with an swr of less
>than 1.3 to 1
> 
>thanks for any help
> 
>chuck, ka1mwp
> 
>the schematic is at
> 
>http://home.comcast.net/~ka1mwp
> 
> 
> 
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