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[SOLVED] 160m mosfet linear amplifier problem with ferrite cores

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tzitzikas

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HI. i have constructed this linear amplifier 500w rms (2kw pep) (50ohm) with 12 mosfet irfp360, https://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??

some pictures
https://tzitzikas.webs.com/linear20a.JPG
https://tzitzikas.webs.com/ferrite_broken1.JPG
https://tzitzikas.webs.com/ferrite_broken2.JPG

the feerite cores that i use are:
https://uk.farnell.com/fair-rite/2643626402/ferritecore-196ohm/dp/1463423
from manufacter:
https://www.fair-rite.com/cgibin/ca...ound+Cable+EMI+Suppression+Cores#select:freq1
Round Cable EMI Suppression Cores
Broadband Frequencies 25-300
MHz (43 material)
some radio amateur told me that maybe this cores are improper for these frequences. But the designer of this linear
claims that we must use 43 material cores for the transformers.
from amidon site:
43 Material Round Cable Beads
* > Round Cable Beads
Suppresses 25 to 300 MHz

31 Material Round Cable Beads
* > Round Cable Beads
31 material. Good for 1 to 300 MHz


77 Material Round Cable Beads
* > Round Cable Beads
Great for RFI in 2 to 30Mhz range
Thank you.
 

Have you a link to the original article other than just teh circuit? I don't understand the winding descriptions such as T3: "5 turns 25r on 1 bead 43 ferrite +1 turn".

What is 25r? Isn't 5 turns +1 turn = 6 turns?

Even T1 "... on 4 43 ferrite beads" could be interpreted in different ways, such as parallel or series.

Keith.
 

keith1200rs said:
Have you a link to the original article other than just teh circuit? I don't understand the winding descriptions such as T3: "5 turns 25r on 1 bead 43 ferrite +1 turn".

What is 25r? Isn't 5 turns +1 turn = 6 turns?

Even T1 "... on 4 43 ferrite beads" could be interpreted in different ways, such as parallel or series.

Keith.
Click to expand...
The presentation of this linear amplifier is in Greek language, but you can see a photo of the prototype amplifier and the T3 transformer. 25r means 25ohm coaxial cable.
http://www.tzitzikas.webs.com/linear_first.jpg


The follwing photos are from the same linear, which have been constructed by other greek radio amateur who claims that is working perfectly.
http://www.tzitzikas.webs.com/linear_working3.jpg
http://www.tzitzikas.webs.com/linear_working1.jpg
http://www.tzitzikas.webs.com/linear_working2.jpg
 

OK, so T3 is a transmission line transformer. I am still puzzled by the "+1 turn". The drawing shows a black line going through the core - presumably the +1 turn, but I am not sure what that represents on the circuit diagram. Is it supposed to be R810 (or is it R8 and 10 ohms)?

With transmission line inductors/transformers you need to make sure you connect them correctly, as shown in the diagram.

It is a while since I have done any work on transmission line transformers although I have the first edition of Jerry Sevick's book on them which seems to be the sole reference on them.

I guess all you can do is wind another, make sure it looks like the photo and try again. In particular, make sure you connect the screen to the core as shown.

Keith.
 

keith1200rs said:
OK, so T3 is a transmission line transformer. I am still puzzled by the "+1 turn". The drawing shows a black line going through the core - presumably the +1 turn, but I am not sure what that represents on the circuit diagram. Is it supposed to be R810 (or is it R8 and 10 ohms)?

With transmission line inductors/transformers you need to make sure you connect them correctly, as shown in the diagram.

It is a while since I have done any work on transmission line transformers although I have the first edition of Jerry Sevick's book on them which seems to be the sole reference on them.

I guess all you can do is wind another, make sure it looks like the photo and try again. In particular, make sure you connect the screen to the core as shown.

Keith.
Click to expand...

look at here to understand how the T3 is connected.
http://www.tzitzikas.webs.com/connections.JPG
the black line is the +1 turn. is insulated wire
R8=10ohm resistor/2watt
 

Ahh. that makes more sense now. My concern would be whether the single turn polarity is correct. If it wasn't though, I would expect you would end up with an oscillator.

Mind you, your picture shows two beads and the instructions say one bead.

Keith.
 

the manufacturer is using only one turn. and the other radio amateur amateur for primary coil of T3. They claim that their amplifiers gives at 110vdc 450-500w r.f power(the current is 13A).
But my amplifier gives only 190w at 106vdc (6A current). The only difference is that i am not use International Rectifier mosfets but Siliconix, and the second difference is that at the output i use 6 ferrite beads instead of them they use 4 ferrite beads. look the pictures

my linear
http://tzitzikas.webs.com/linear20a.JPG

prototype
http://www.tzitzikas.webs.com/linear_first.jpg

another amateur
http://www.tzitzikas.webs.com/linear_working3.jpg
http://www.tzitzikas.webs.com/linear_working1.jpg
http://www.tzitzikas.webs.com/linear_working2.jpg

Do you believe that the +2 ferrites i am using in output transformer are responsible that my amplifier give not much more power?
 

tzitzikas said:
Do you believe that the +2 ferrites i am using in output transformer are responsible that my amplifier give not much more power?
Click to expand...

I really don't know. I have had a quick look through my transmission line transformer book and it never uses multiple ferrite, so I am not sure of the effect.

Some of the pictures seem to show twisted pairs instead of coax for T3.

Are you sure your connection of the single turn on T3 is correct?

Keith.
 

you can see the prototype photo and T3 photo for the connections
 

Hi
You can't use 43 up to 160Mhz. Obviously it will be broken.... Any more, that's why you can't get higher power.
You can try 61.. Good luck.
 

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