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.
---------------------------------------------------------------------
http://tzitzikas.site90.net (tzitzikas site)
http://forum.tzitzikas.site90.net (tzitzikas forum)
---------------------------------------------------------------------
--- 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, 4:49 AM
Are you using the same manufacturer as your friends?
If so, yours should be the similar performance unless
something is wrong.
David
----- Original Message -----
From:
sasas
asasas
To: amps@contesting.com ; David
Cutter
Sent: Sunday, April 18, 2010 12:12
PM
Subject: Re: [Amps] 160m mosfet linear
amplifier problem with ferrite cores
hi. i am not use insulators between mosfet and heatsink in order to have
the minimum thermal resistance. I
am using only silicon thermal conductive paste to
decrease the thermal resistance. So, the heatsink is connected with the
drain of each mosfet and the
heatsink has the drain voltage.
I am
using 12 Siliconix's IRFP360 mosfets, but i have order and soon i will
replace them with International Rectifier IRFP360 mosfets. Propably
this
is the reason, that the amplifier don't give many watts at
outupt.
The other reason, is that the material of ferrite cores (43
material) is not the proper for 1-2mhz frequences. What do you
think??
--- 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, 3:50 AM
I see you are using hex socket screws. It
is very easy to over-tighten screws to fix plastic devices to a
heatsink, I've seen them crack after a little time in the field due
to
expansion and contraction against an over-tight fixing. The
crack can be invisible to the naked eye initially but causes
failure of the device. Mounting torque is 1.13Nm which is quite
low.
The mounting tab is the drain and you could look
at the heatsink isolation. Is there an isolation insulator
under each device or is the whole heatsink
isolated?
I could be drifting off the subject, but fixing
small errors can often chase away the big ones.
David
G3UNA
-----
Original Message -----
From:
sasas
asasas
To:
amps@contesting.com ; David
Cutter
Sent:
Sunday, April 18, 2010 10:41 AM
Subject:
Re: [Amps] 160m mosfet linear amplifier problem with ferrite
cores
Some additional photos from my
linear:
http://tzitzikas.webs.com/fet20.JPG
http://tzitzikas.webs.com/linear20.JPG
http://tzitzikas.webs.com/linear21.JPG
http://tzitzikas.webs.com/linear22.JPG
http://tzitzikas.webs.com/fet21.JPG
http://tzitzikas.webs.com/pompos20.JPG
---
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, 2:35
AM
I've looked again at the jpg and I
think you have used trifilar windings, so, that's my
first idea more or less gone. Imbalance can be
due to poor coupling between the windings themselves or
imbalance in the driving currents. With high voltage
supplies, balance error should be small (compared to say a
12V amplifier where a small difference in voltages can show
a large imbalance %). If you could measure the current
in each half of the primary that would tell you the whole
story: you will need a HF current probe, preferably 2
probes
and dual trace scope which will also tell you about
cross-conduction.
Another thought: you have 6
transistors in parallel in each half and emitter (sorry
- source) degeneration. Did you try matching the
FETs for gain or phase delay? If not, it's conceivable
that one side is conducting harder or for longer than the
other side and causing an imbalance. I don't know if
the source resistor is the optimum value for
mis-matched FETs, but a higher value would increase
negative feedback and help with this; you have oodles of
gain to sacrifice. Along the same lines, the input
drive to each FET may need optimising for the same
reason. Check all your resistor values, one might
be a dud.
This is all armchair speculation, I
don't have enough experience for better detail.
Someone with modelling experience could probably do this
quite quickly.
Alex has probably got the answer
regarding core material.
David
G3UNA
-----
Original
And how can i repair this
problem???
You might consider imbalance
in each side of the primary which will cause a
net
dc to pass, saturation and over-heating.
This may be rubbish but it could get others
thinking along a different
path.
David
G3UNA
> HI. i
have constructed this linear amplifier 500w rms
(2kw pep) (50ohm) with 12 mosfet irfp360,
http://tzitzikas.webs.com/linear500w.jpg
for 160m band.
> When i gave 3watts of
driving r.f power, it gave to output only 190w at
106VDC (6A current). Two radio amateurs who have
construct this linear claim tha it gives
500w
> r.f power at 110vdc.
> But when
i tried to give 4watts of driving r.f power the
ferrite Cores (43 material)
> of transformer
T3 broken! Which do you think is the
problem??
>
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