If you don't disconnect the parallel fixed padder across the C2 in the
Pi-network on 14 MHz,
you may end up in serious heating trouble, as well as using a very unsuitable
operating point for the PA tube.
The pi-network calculations for a tube this size calls for
a C2 in the order of 200 - 250 pF on 14 MHz for a loaded Q of 12.
600 pF results in a loaded Q in the range of 25 - 30, and the coil losses will
be in the order of
5 - 10 times higher than normal due to the fact that tank circuit losses are
proportional to the square of the circulating currents. They are in turn
proportional to loaded Q.
A doubled loaded Q means 4 times higher coil losses.
73/
Karl-Arne
SM0AOM
----- Original Message -----
From: "Partain, Chuck" <Chuck_Partain@maxtor.com>
To: <amps@contesting.com>
Sent: Thursday, May 11, 2006 1:54 AM
Subject: [Amps] tank coil heating
> 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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