hi. The manufacturer and another radio amateur claim that this linear amplifier
which they have constructed works perfectly and stable, and gives 400w minimum
r.f power at output stage (with 110vdc power supply-13A the current). i don't
know spice simulation.
The linear which i have construct gave to the output stage (at 50hm dummy load)
190w r.f power with perfect modulation with 106vdc power supply. the current in
this test was 6A.
The problem witch i am trying to solve is to find why my linear gives only
190watt at the same voltage, and why every time i was trying to increase the
input r.f power, up to 4 watts, the circuit get into oscillation and the
ferrite broken. Something goes wrong but i can't find what exactly.
The only difference between my amplifier and the prototype is that i use 6
ferrite beads at output transformer and the designer of the prototype uses only
4, as you can see in photos.
The other difference is that i am using Siliconix IRFP360 fets and the designer
of prototype using International Rectifier fets. Moreover his operate frequency
is 1650khz and my operation frequency is 1431khz. So i worry if i must use
another ferrite material of 43, something like 77 material.
What do you think?
--- On Tue, 4/20/10, Boye Christensen <oz7c@cool.dk> wrote:
From: Boye Christensen <oz7c@cool.dk>
Subject: Re: [Amps] 160m mosfet linear amplifier problem with ferrite cores
To: "sasas asasas" <tzitzikas_ee@yahoo.com>
Date: Tuesday, April 20, 2010, 9:47 AM
Hi
Have u tried to run a simulation e.g with spice
to se if this works ???
You can dowload LT spice free to try ?
As far as I can se this fet with 2 x6 pcs will not work
Ciss 4.5nF * 6
Crev 490pF *6
Cout 1100pF *6
a lot to control !
http://www.vishay.com/docs/90292/sihfp360.pdf
73 Boye OZ7C
----- Original Message ----- From: "sasas asasas" <tzitzikas_ee@yahoo.com>
To: <amps@contesting.com>; "'David Cutter'" <d.cutter@ntlworld.com>; "Alex
Eban" <alexeban@gmail.com>
Sent: Tuesday, April 20, 2010 5:09 PM
Subject: Re: [Amps] 160m mosfet linear amplifier problem with ferrite cores
> the manufacturer who construct the prototype and use mica to the fets,
> propose to me. to not use mica, but to take the drain for the 6 fets from the
> heatsink. He told me just to use some thermal silicon paste for low thermal
> resistance.
>
> --- On Tue, 4/20/10, Alex Eban <alexeban@gmail.com> wrote:
>
> From: Alex Eban <alexeban@gmail.com>
> Subject: RE: [Amps] 160m mosfet linear amplifier problem with ferrite cores
> To: "'sasas asasas'" <tzitzikas_ee@yahoo.com>, amps@contesting.com, "'David
> Cutter'" <d.cutter@ntlworld.com>
> Date: Tuesday, April 20, 2010, 2:32 AM
>
> First of all the guy INSULATED the FET's from the heatsink!
> You can see the mica insulators of the side plate where the transistors are
> mounted.
> He also used a WIDE copper strip to connect the drains; parallel connected
> FET's are notorious for breaking into oscillations using the stray inductance
> of interconnecting wires as a resonating circuit. I've seen a pair of them
> running off merrily at about 80 MHz , in a circuit supposed to work at DC!
> It's probably more an issue of the way it's built than a real electrical
> problem. If stray coupling causes oscillations, then it can also explain the
> cracked cores in the output transformers.
> My recommendation is that you rebuild it along Tzitzika's model, with good
> short wiring, insulated transistors and good bypassing.
> It's like cooking: first time copy the recipe exactly. Improvise on the
> second run! At these power levels it takes very little to go from a working
> circuit to a catastrophe!
> Alex 4Z5KS
>
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of sasas asasas
> Sent: Sunday, April 18, 2010 3:05 PM
> To: amps@contesting.com; David Cutter
> Subject: Re: [Amps] 160m mosfet linear amplifier problem with ferrite cores
>
> The linear have been constructed by me (if you mean the manufacter of linear
> amplifier).
>
> The prototype have been constructed by schematic designer and you can see a
> photo here:
>
> http://www.tzitzikas.webs.com/linear_first.jpg
>
>
> Also, this linear have been successfully constructed by another radio
> amateur. You can see photos here:
>
> http://www.tzitzikas.webs.com/linear_working3.jpg
>
>
> http://www.tzitzikas.webs.com/linear_working1.jpg
>
>
> http://www.tzitzikas.webs.com/linear_working2.jpg
>
>
> Both of these linear are using International Rectifier IRFP360 mosfets.
> I use this time Siliconix IRFP360 mosfets. Both of amateurs claims that their
> linear amplifier gives at least 450w r.f power at the outupt stage.
> --- On Sun, 4/18/10, David Cutter <d.cutter@ntlworld.com> wrote:
>
> From: David Cutter <d.cutter@ntlworld.com>
> Subject: Re: [Amps] 160m mosfet linear amplifier problem with ferrite cores
> To: "sasas asasas" <tzitzikas_ee@yahoo.com>, amps@contesting.com
> Date: Sunday, April 18, 2010, 4:56 AM
>
>
>
>
>
>
>
> Are you using the same manufacturer as your friends?
>
>
> If so, yours should be the similar performance unless something is wrong.
>
> David
>
>
>
>
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>
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>
>
>
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