60w rf amplifier

[Ziddik]

the one who drew this schematic says this circuit has 60W Rf output power using a single IRF840 Power mosfet! Is it true and does this circuit work?

This is what he said in his website

""The IRF linear amplifier can be
connected to the out put of
popular VWN-QRP to get an
output of 60 Watts. The circuit
draws 700 ma at 60 Volt Vcc.
Good heat sink is a must for the power transistor. Alignment of the circuit is
very easy. Connect a dummy
load to the out put of the
circuit. You can use some small
bulb like 24V 6Watts as the
dummy load. I have even used 230V 60Watts bulb as
dummy load with my IRF840
power amplifier working at
120Volts. Adjust the 10K
preset to get around 100 ma
Drain current. I used gate voltage of 0.8V with my
linear amplifier. A heigh gate
voltage can make the power
transistor get distroyed by
self oscillation. So gate voltage
must be below 2V and fixing at 1V will be safe. Bifalar transformaer T1 is
wound with 8 turns 26SWG
on 1.4 x 1 balun core.
The coil on the drain of IRF is 3
turns 20 SWG wound on 4
number of T13.9 torroids (two torroids are stacked to form a
balun core). The RFC at the Vcc
line is 20 Turns 20 SWG wound
on T20 torroid.Thank you""

 

[Mikebits]

The IRF840 is a power fet not an RF device.

 

[Ziddik]

so, doesn't this circuit work? He lied then, right?

 

[carbonzit]

That must be from one of those notoriously unreliable Indian electronics sites that Colin talks about, eh?

Ziddik, you need to learn to apply some common sense on your own.

The author says:

The circuit draws 700 ma at 60 Volt Vcc.

So how much power is that? Do the math for us.

 

[Ziddik]

That must be from one of those notoriously unreliable Indian electronics sites that Colin talks about, eh?

Ziddik, you need to learn to apply some common sense on your own.

The author says:



So how much power is that? Do the math for us.

thats what i am talking about.. Most of this author morons dont make any sense!!

 

[carbonzit]

You need to keep in mind the age-old advice: "If it sounds too good to be true, it probably is."

 

[Ziddik]

You need to keep in mind the age-old advice: "If it sounds too good to be true, it probably is."

why dont u go and stick around with a 1.5v battery and some leds? Maybe u will surprise when the led glows

 

[geraldfryjr]

When setup properly as a Class E amplifier the IRFxxx FET's work great!

jer

 

[4pyros]

Yes it is a old indian ham radio circuit thay made in the 80s with parts thay had and it worked.
I dont know about 60 watts but it worked for them with what thay had at the time.
You can do alot better with newer parts ment for RF amplification.
Andy

 

[Ziddik]

so does the circuit work?

 

[geraldfryjr]

Yes, those FET's will switch well into the RF range !
Just Google up Class E Amplifier there is a ton of stuff!
There is a site that is dedicated to such amplifiers.
There was an article that was published in QRP that got 500watts out of a IRFP460.
There also is a program that will help you determine the parts values in the circuit based upon the parameters that you enter.
If done right it is much cheaper than some rf devices But remember that these are Class E and are not A or AB linear type amplifiers and will require a modulation circuit for AM mode.


jer

 

[Ziddik]

does it work on 88~108mhz FM band? ..would give a try if it does..

 

[alec_t]

does it work on 88~108mhz FM band? ..would give a try if it does..

And cause interference to annoy legitimate users of the band? That's rather anti-social (and probably illegal, depending on the country you're in).

 

[geraldfryjr]

Rarely have I seen hexfet's used in anything above 50mhz.

 

[4pyros]

does it work on 88~108mhz FM band? ..would give a try if it does..

As far as I know its only been tried with AM. Why would you even what to try it with FM, its a sh#$% amp.

 

[geraldfryjr]

Actualy it is more suited for FM use than anything else.
It is one of The more efficient designs of today, >90%.
It can be a little tricky to understand and setup.
But it was the First time 500watts of RF power came from a $3 part.
Show me a dedicated RF device that can do this for $3 or less!
It has also been know to emit less harmonic radiation than some of the older standard designs without the extra filtering on the output.
It made its debut in the 80's.

jer

 

[Mikebits]

That FET is full of parasitic capacitance. CGD and CGS thus rendering them unsuitable for RF. Look up miller capacitance.

 

[4pyros]

It made its debut in the 80's.

Can you show us?

 

[geraldfryjr]

Yes,some FET's have a high gate capacitance and are unsuitiable for rf use ,Because of this they can take as much power to drive them as they produce.
They must be drivin by a low impedence source in order to generate enough current to charge and discharge the gate's capacitance at high frequency's.
I will try to dig up some links for you to check out.

jer

I had made a mistake in an earlier post and said that the article was in QRP it was not,It was in QST magazine,Sorry for the miss info.

 

[Ziddik]

i know its illegal to use such a high power transmiter but i just want to know if anyone of u had any experience with them..