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Problem with output power-linear amplifier
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tzitzikas
electronics forum beginner


Joined: 20 May 2010
Posts: 2

PostPosted: Thu May 20, 2010 3:32 pm    Post subject: Problem with output power-linear amplifier Reply with quote

hi, i have construct this linear amplifier for mw band: http://tzitzikas.webs.com/linear500w.jpg with 12 mosfets IRFP360.
some photos from my project here:
http://tzitzikas.webs.com/linear_photo_1.jpg
http://tzitzikas.webs.com/linear20.JPG
http://tzitzikas.webs.com/linear20a.JPG
http://tzitzikas.webs.com/linear21.JPG
http://tzitzikas.webs.com/fet21.JPG
http://tzitzikas.webs.com/pompos20.JPG
http://tzitzikas.webs.com/T3.JPG (photo of /t3 broadband transformer)

for ferrite beads i am using FB-43-7351 from https://www.amidoncorp.com/items/44 but i have also orderedFB-43-7352 and the FB-43-1020 ferrite beads.
The manufacturer claims that with only 2w input r.f power it gives 500w at the output at 110vdc (13A current). But with 5,5w input power at 106vdc my linear gives only 220w output r.f power (7A current) at dummy load 50ohm.
(here you can see a photo from prototype: http://tzitzikas.webs.com/linear_first.jpg )
Also, the other problem is that the T3 transformer and the resistors R9,R10,R11,R8 and the r.f choke VK200 are very warm when the linear operates.
But the basic problem is to increase the output power.
The mosfets are from Siliconix but i have ordered and i will try to use International Rectifier's IRFP360 mosfets.
Do you have any idea what is the problem for the low output power? Do you have to propose any change to broadband transformers to increase the output power? I tried to change the value of C4=3,9nf capacitor but the output power was more low.
Thank you.
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