[Swan] WtB Swan sw-240

Kenneth G. Gordon kgordon2006 at verizon.net
Thu Jan 24 20:53:59 EST 2008


On 24 Jan 2008 at 13:42, Rick Gouge wrote:

> Hi all. I am looking for a swan sw-240 tri bander for parts. must
> still transmit because those are the parts i need. I am sure the
> problem is in the final section. Had an RF fire for a brief moment in
> the final cage when i was on AM. Transmitter still works but it will
> not tune so i can have 160 ma.

UNDOUBTEDLY, your final RF choke is a large, spiral-wound piece of 
carbon by now. The bypass capacitor at the bottom of the RF choke is 
simply bypassing all your RF to ground.

If the RF choke is open, the screen grids of the final amp tubes are 
probably toast as well.

A Swan 240, when operated on AM, shouldn't be loaded to more than 60 
watts input. 

160 mA, if your plate voltage is around 700 VDC, would be 112 watts 
input. If it is 800 VDC, that would be 128 watts input, which is a +100% 
overload for the rig in AM.

Even at 600 VDC, 160 mA would be almost 100 watts input (96 watts).

If you have been running it at 160 mA, no wonder it burnt up.

At 800 VDC on the final, you shouldn't load it to more than 75 mA on AM, 
and if your power supply puts out 600 VDC, then 100 mA is maximum 
input.

I would the check final amp plate RF choke and replace it, and check the 
final amp tube(s) screens to see whether or not they still exist.

Good luck.

Ken Gordon W7EKB


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