MRF186 good for 120w maybe this with MRF9180 push 200w

Made a start with the amp. Then hit a wall as the kit was missing a length of 25ohm coax, which isn't available locally. So it'll have to be eBay.

No expense is spared. Had about 5mm spare wire after winding the coils.

There was also a 10ohm and 1k resistor missing.








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The amp will easily do 200W+ on only 24V! The gain on this design is insane!


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Maximus wrote: ↑Thu Mar 02, 2017 10:11 pmThe amp will easily do 200W+ on only 24V! The gain on this design is insane!

Be careful, that FET is fragile - don't breathe on the input! That board is OK for the price but could be improved. The bias is critical and varies significantly with temperature and the output circuit is quite basic and would benefit from techniques to improve linearity. It's not as linear as the manufacturers suggest and not uncommon in amplifiers of this type for around 10dB more 3F than 2F. For this reason, and the look of the filter, I'd be surprised if your measured 200W is all on Band II.

Yes I found out the hard way with the bias.

Fitted a Freescale transistor and the thing is rock solid.


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Some more pictures








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I have a version of this board made for the MRF186. Can I just swap in the MRF9180 for more power output? It seems to run at the same voltage and matching on these devices seems pretty generic, so it should work right? Maybe just some bias adjustment?

Yes AFAIK the boards and components are the same. The bias may need adjusting though.


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So I found these boards on ebay and it looks like they're using the MRF9180. They are using an extra coil between the two drains and also two resistors. Do you think adding that on your design might improve things? Surprised they only say 150W though.

Anyway I just bought some MRF9180s to replace the MRF186 to see if I can get more power. What should I adjust the bias voltage to?

I think the extra coil and resistors are in place to stop the thing 'taking off' if the bias or drive would suddenly develop a mind of its own. Probably isn't critical.

Can't remember the exact bias voltage, but I know the variable pot barely adjusts it.

Also had different results from the transistors. The supplied (used) Motorolas were absolute crap and kept on popping. The Freescale versions are very reliable and rugged.

You can easily push 200w into a good matched load without harmonics. I wouldn't recommend going much over 150w as the transistor runs cool and can easily survive a big mismatch (using Freescale).



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With a few modifications, the amps have many other uses. Especially DAB, when combined with some good filtering on the output.


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hello from me guys!few questions for 9180 mdifications!how much amps needs?any changes of materials in output filter?or the same values?bias voltage?cables of 25ohm doesnt burns?

Hello Mr Steven!
As far as I know? the 9180 is interchangeable with the 186 with no modifications? Teflon based coax will be fine for this design!
As mentioned several times! Bias voltage cannot be specified for any given design! The important part is the drain quiescent current, When the transistor goes from an off state to conduction? This varies with devices and would normally be around 100ma for class B operation but as it is dual FET 200ma would normally be seen?
You need to monitor the drain current (with no RF drive) and set the bias voltage accordingly!

sir sinus
thannks for responce and answer some of my questions!if i put dirctly 9180 vs 186 what i take from this change with the same volts,ampes?

Hello Mr Steven! Glad to help!
I could just tell you the answers? But you would not learn anything that way!
To get a grasp of what you are dealing with? The datasheet is always a good start! One thing you have to bear in mind is the manufacturer will deal with absolute maximum ratings in a perfect environment! In your application this will not be the case, it will likely be half of their figures!
Take a look at this regarding bias!
When we look at the ON state characteristics? we can see that the Vgs(th) in a common source configuration @ Tc=25c is between 2 - 4v? But its Vds is only 10v (supply voltage)
Now the max voltage I would expect you to use is 24 - 26v supply! I would still stick to an absolute max gate bias of 4v just to be safe!

Now how much current will the whole assembly consume in operation assuming the Vds stays constant? And you want 170watt out? In a fantasy world, the transistor would be 100% efficient and only draw 170watt from your PSU?
The reality is that at best the transistor will only be 75% efficient? Therefore your transistor will be dissipating around 215watts!

215w divided by 24v = 8.95A So you would need atleast a 10A PSU to achieve anything near that output!

thanks again sinus for answers buddy!!!!i lost for moment 2 mrf186 without reason probably some of them in put drve with 3,5watt !!!any tip to safe the features one?some resistor in gate(resistor safe )?any tip also in input or output stages?i put 100pf across in 10ohm resistor and push it to get more power with this change!

I don't know where to measure the current. So I guess I can't just power on the amplifier with no drive and measure the current from mains. I get 800ma when I do this. It looks like there is a bridged pad under the teflon balun leading to the drain of the mosfet. Should I measure here?

OgreVorbis wrote: ↑Sat May 27, 2017 8:19 pm I don't know where to measure the current. So I guess I can't just power on the amplifier with no drive and measure the current from mains. I get 800ma when I do this. It looks like there is a bridged pad under the teflon balun leading to the drain of the mosfet. Should I measure here?

Hi Mr, OgreVorbis. Here's a link to a radio amateur who describes how to trim the 100Watts RF final stage with MRF186 and I'm going to do the same with MRF 9180. Have a kit with MRF 9180 but has not built it yet.
http://g4fev.atspace.com/mrf186linear.htm

Thanks for the link. It'd probably explain a few problems that I've been experiencing with the amp.


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Maximus wrote: ↑Thu Mar 02, 2017 10:11 pm The amp will easily do 200W+ on only 24V! The gain on this design is insane!


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Hi Maximus,
Have you got 200W out of MRF9180, I only get 150W and I feed my with 27V.
Has set the total bias to 350mA, has tested 400mA but it does not give much more anyway. The drive power is 1.5W so it should suffice because with MRF186 I have 100W. What bias current have you set? according to the data sheet, it should be set with 2x700mA.