BLF177 solid state HF Linear Amplifier

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BLF177 solid state HF Linear Amplifier

Post by VK4DD » Wed Apr 22, 2009 8:56 pm

Hi All,

I decided it was time to make a solid state amp for HF and possibly 50Mhz as well.
After looking at the pros and and the cons of many different devices I settled for the BLF177.
A very rugged Fet with a max VSWR of 50:1 and it is also an NXP/Phillips fet so very good quality.

The whole idea is not just based on theoretical simulations, no it is based on a Phillips application note which decribes the whole amp.
I compared this with the a similar concept from Motorola and am favouring this design.

One PCB runs of a 48V power supply. The minum power supply for 1 PCB is 600W but if you combine two boards a 1500W switched mode would be a smart choice.
That would give you 600W to 700W output power.

The PCB's are right now produced and I expect them to arrive in a week or 2.
Just in time for the Barcfest here in Brisbane.

The BLF177 is between 50US$ and 60US$ so quite affordable too, especially if you consider that they are tough devices, compared with other Fets.

Have a look also at the attached the application note.

You can contact me if you need circuit boards. High quality, professionally made boards produced in the factory.
A singel amp will roughly 10W drive for 300W out, but knowing NXP the output will be higher than just that.
Please read the attached application note for more details.

Will it do 50Mhz?
According to the application note the current amp rolls of at 40 Mhz but the Fet can easely do 50 Mhz.
As such higher frequency response has to be found in use of different ferrite material.

BLF177 HF PA.pdf
The Phillips application note
(164.59 KiB) Downloaded 1327 times


Re: BLF177 solid state HF Linear Amplifier

Post by VK4DD » Mon May 11, 2009 1:58 pm

Hi Gents,

The all new 2 x BLF177 HF Printed Circuit Boards have just arrived.
The big hole in the center is for a temperature switch.
In the centre of the PCB near the devices an temperature switch is mounted.
These switches are sold by Jay Car.

The board is based on a Phillips application note. So you will have lots of documentation on how the amp is designed and how to build it.

I have made vey little changes to the original Phillips board but are a few things I have changed.
I have allowed for 2 bias trimmer resistors. That will allow you to use also not matched pairs.
You can set the bias current up for each individual BLF177.
I have added a cut out near the Fets were you can mount a standard temperature switch.
Jaycar sells these things and you can mount one the heat sink.
It is nice to have such a switch so close to the Fets. Of course you can also mount a temperature sensor.

This PCB is now available in my web shop, and in the short time that it has been there it has been an absolute winner.
I am surprise how quickly these boards are snapped up by Hams. Apparently there is quite a big group of builders on HF/50 Mhz intrested in these.

Last edited by VK4DD on Thu May 14, 2009 7:31 pm, edited 2 times in total.


Re: BLF177 solid state HF Linear Amplifier

Post by VK4DD » Wed May 13, 2009 6:49 am

Hi Gents,

I got some feedback from Fred N1DPM. Fred writes that he has seen a pair of BLF177 in the Harris FM broadcast transmitters running 500W.
Off course this is in Class C. But than again it shows how special these parts are. Phillips has rated them as 150W devices and Harris uses them commercially at 250W per device.
I have never seen that with a Motorola device. So don't be fooled by these BLF177. It's brute power and build like a tank. It is a very nice part and that is basically the reason why I made these boards.

Fred has send me a picture of a modified Harris board which he converted to 6m amp doing 450W. The inductance in the output circuit is created with 2 thin 50 Ohm coaxes parallel.
As such you get a 25 Ohm. A very basic amplifier circuit. The same can be done for 2m as well, except the coax would be shorter.
Probably no reason why you could not fit this on the circuit board I have, if you like to experiment. On the input you have to make a different input design or use the design from the application note and tweak the capacitors or the ferrite. I have asked Fred to make a sketch of what he has done, and I will post that when I receive the info.

Harris has mounted these devices on a copper heat spreader, probably because they going to the limits. I was just planning to mount them direct onto an aluminum heat sink this time and run them very conservative at 300W. If you want to push them to the end, than it is probably best to mount them on copper.

73 Ron
6m amp with 2 x BLF177 (450W out)
6m amp with 2 x BLF177 (450W out)


Re: BLF177 solid state HF Linear Amplifier

Post by VK4DD » Tue May 19, 2009 10:11 am

Hi Gents,

I got some questions about splitters and combiners for HF.
I found a supplier who can combine 2 boards for HF.

They got 2 port combiners for 1kW out.
They also have 2 port combiners for 600W out.
It is up to you which one you use. I would probably go for the 1kW out 2 port one.

They also have 4 port combiners, max 2kW out.
This would combine 4 HF amplifiers.

Picture 1: An example of a ready made HF only combiner for 2 PA boards.
Unfortunately 6 m is not covered by these combiners.
May be if you change the ferrite to material 61, it would do the job.
This is something I suggest to discuss with RF power systems

First attachment: Application note from Phillips for making your own combiners.

LAST BUT NOT LEAST.... where do i get parts, fets etc etc....

Second attachment. These are suppliers you can use to source my bits for the BLF177 amp.
Not limited to the BLF177, the ferrite etc.

73 Ron
Notes on materials BLF177 PA.xls
Preliminary... where do I buy the parts for this project...
(9 KiB) Downloaded 849 times
1kW combined 4 x 300W.pdf
Application note Phillips
(58.79 KiB) Downloaded 1633 times
An example of a ready made 2 port combiner for HF
An example of a ready made 2 port combiner for HF


Re: BLF177 solid state HF Linear Amplifier

Post by VK3XIL » Tue May 19, 2009 3:11 pm


Communications Concepts have a similar product




Re: BLF177 solid state HF Linear Amplifier

Post by VK3XZ » Fri Jun 26, 2009 12:26 pm

Hello all,
I am looking for someone who is building this HF amp on Rons(VK4DD) boards. I now have my power supplies, FET's and boards with some parts. I am planning to use a 12 inch version of thw 2 meter heatsink and will be using copper spreaders purchased on this forum. I am using Rons Pic board and Display for remote control of the amp. Is there anyone out there who can give a progress report on their amp? I am needing to know in case of any issue encoutered. I still need parts for the amp. I will usue 61 Material to try and get it to work on 6 meters also. Thanks for any advice, updates you can give. My Mobile in melbourn e is 0408584410


Re: BLF177 solid state HF Linear Amplifier

Post by VK4DD » Sat Aug 01, 2009 11:35 am

Hi Gents,

I received a question where the all the components go for the bias circuit.
I could not use the lay out of the Phillips application note since they use only one bias potentiometer.
This forces you to use matched pair FETS etc.

That was the reason I just doubled the bias circuit and came up with this solution for the lay out.

The big hole in the center is for a Thermostat (bi metal).
You can leave it out, or make a protection with it. That is up to you.

Note that some components are doubled... like R3, R4, R5, R6 and C3 and C6.
I have drawn a red wire which connects the two bias supplies of both Fets.
That will go to a sequencer board. Which turns the bias on and off.

The rest of the lay out is identical to the Phillips application note.
So I suggest to keep using that.

73 Ron
lay out bias circuit.PNG


Re: BLF177 solid state HF Linear Amplifier

Post by VK4DD » Thu Nov 05, 2009 5:35 pm

Hi Gents,

I did some work on the HF/6m amplifier and sweeped the input with my home brew VNA.

Why am I doing this?
I like to test amplifiers without voltages or Fets soldered in place.
This is a safe way to experiment and it allows you to get a feeling of what is going on before you go "live".

Here is the used method....

I had no BLF177 soldered in place in stead I looked up what gate capacity they had and soldered these to gnd.
Also I made a temporary bridge between the pad with the 4 resistors to the gate.
This should represent the input impedance of the FET.

I first wound the coil as per the application note, and found that it was a bit hard to constuct.
It is so tiny and keeping the coupling between the winding nice was too difficult for me.
So here is what I ended up doing. I had a binocular ferrite. (A binocular piece of ferrite is a piece of ferrite with two holes in it).
I made a 4:1 balun (so 2 winding: 1 winding). I will show you later some detail pics. It is actually a very easy to construct balun.

Any way here is what happened... the VSWR for HF to 30 Mhz was good but above 35 to 40 Mhz the VSWR went up ...
almost upto VSWR 3:1 on 50 Mhz. Even other compensation caps or the trimmer cap had not much influence.
After some experiments I noticed that the balun wanted to see a bit more inductance for 50 Mhz.
(Hey it is so nice to have a VNA in the shack :) but instead you can also use a simple antenna analyser and measure the VSWR :idea: )
Resulting in a return loss of -18dB on 50 Mhz, -18dB on 30 Mhz and better towards 14 Mhz.
The worst VWSR was at 1.6Mhz about -16dB return loss.

Results are pretty good... The frequency range from 1.6 to 50 Mhz is huge for 1 piece of ferrite.
I had to use some frequency compensation techniques to extend the frequency range beyond the 50 Mhz.

Please note in this topic I prefer not to talk about my home brew VNA. If you have questions about it than send them to my personal email address.
That will keep this posting easier to read for others who are experimenting with these circuit boards as well.

I mention experimenting because that is what I do as well.

As far as the scale... the best way to read this graph is to look at the VSWR at the markers in the top left corner.
The numbers in black represents the frequency and the numbers in blue represent the VSWR.
The grey bottom line is VSWR 1:1 the grey line in the middle is VSWR 2:1 and the grey line on the top is VSWR is 3.
The horizontal axis is the frequency starting at 1 Mhz (linear scale middle is 30 Mhz) and the end is 51 Mhz.
The markers will help to read you this as well as they are positioned at strategic points.

Will post the the modification to the PCB shortly (just a piece of wire inserted to form a small inductance).

Any way I am pretty pleased with this result so far :)

73's Ron


Re: BLF177 solid state HF Linear Amplifier

Post by VK4DD » Mon Nov 09, 2009 5:35 pm

Hi Gents,

Just done a little bit of work on the output circuit this weekend using a home made ferrite core from material 61.
Different also from the one in the application note but much easier to wind and to make :).

The idea was to see if it works on 50Mhz ... and it does with material 61 :mrgreen:
It is lacking some inductance on the lower bands and that is why I have lost 1.6 MHz in the attempt to use 50 Mhz.
I suppose that the balun can be made a bit bigger and if you double the length of the core than perhaps 1.6 Mhz can be used as well.
But I haven't tried this. If you don't operate on 160m than I suppose you could build it like this.

I will document later what exactly I have done, and I will also show you how you can measure this at home using simple instruments.
You won't need a vector network analyzer... that is just handy to make a pretty picture that is all.
Off course if you have one than you can over see the whole band in one view.
But don't stop experimenting because you haven't got a VNA... you don't need one to get it right.

Basically I soldered 4 x 27 Ohm and 1 x 330 Ohm (parallel = 6.25 Ohm) to ground simulating the BLF177. I also soldered a 240pf (220pf in my case) to gnd.
This is the impedance of the FET as per the model (see also application note).
Just see it as a dummy load. All the 2:1 transformer has to do is match this to 50 Ohm.
As such you could run a little bit of power into the rear of the amplifier with a QRP rig, or antenna analyzer or a Vector Network analyzer to see what the impedance is.
Very simple, no difficult stuff :)

I did the measurements and optimized the compensation capacitor over the ferrite balun to get a good VSWR across the band.
That is all...
If you see what I have done that you will realize there is no difficult stuff going on.
Just testing the amplifier without a FET, before I solder the fet in place.
This gives me a better idea what goes on in the amplifier.

VSWR is good (read return loss) across the band from 80m to 50 Mhz.
160 m can't be used because of high return loss. That is the sacrifice I make with this solution.
(note that with twice as much material 61 cores this might be different again).

Happy so far... I think it going to work like a rocket :wink:

As far as the VSWR... Granberg (former chief design engineer Motorola RF) who is an authority on solid state amp designs uses VSWR 2 or even above than at the band edges from some of his designs.
All it means is that the Fet has slightly less efficiency at the frequency. But most of the time you will find that fets work better on lower frequencies, so it would not surprise me
that the efficiency on 80m is better than on 50 Mhz. These FETS are specified VSWR 50:1 as such no drama with this load.
At the end of the day the real impedance of the FET will be slightly different. Fets used in broadband amplifiers are made so that they can cope with this.

The plot of the output circuit looks good. 80m starts off with a VSWR of 2:1 but most bands upto 50 Mhz are below VSWR 1.3 and a nice and flat over most of the frequency range.
I think this should work perfect.

73 Ron
BLF177-mod_vk4dd_61_Output circuit sweep.PNG


Re: BLF177 solid state HF Linear Amplifier

Post by VK4DD » Mon Nov 09, 2009 5:53 pm

Hi Gents,

Well it is getting better... I just tweaked it a little bit better with a 1nF capacitor in series with the output.
Resulting in a VSWR of 1:1.65 on 80m 8) and down to 1:1.08 on 40m remaining quite flat across the band.
On 50 Mhz a VSWR of 1:1.21 perfecto :mrgreen:

See attached graph.
Hey this is fun to tweak the amp :D

BLF177-mod_vk4dd_61_Output circuit sweep_mod2.PNG


Re: BLF177 solid state HF Linear Amplifier

Post by VK4DD » Tue Nov 10, 2009 11:02 am

Hi Gents.

Here is a link to the input ferrite I used.
Just one of these 2-hole binocular type core.

For the input ferrite I used a BN-43-202. When I make 2 windings I measure 13 uH.
But when I enter 2 windings in the calculator on the page below It calculates 8.8uH.
Normally the margin from batch to batch is about 40% so don't be surprised when you measure a different inductance.

Will also need to look up what the Amidon part number is for the material 61 output ferrite.

73 Ron


Re: BLF177 solid state HF Linear Amplifier

Post by VK4DD » Wed Nov 11, 2009 10:09 am

Hi Gents,

The output balun I used is made from material 61 ferrite. It is know as part number FB-61-6873.
Amidon calls this type of ferrite a "round cable beat".

You can use it to put a round a cable or use it in a power transformer in an amplifier.

I found it on this page.

I used 150pf compensation over the terminals of the balun to get a nice flat SWR curve over the whole range.
Too much capacity will overcompensate. Under or over compensation works on some frequencies it does not work well over the whole frequency range..
As such you got to experiment to find that capacitor that will do that for you.

It is best to solder the items on the PCB and test the SWR measuring into the circuit.
You could use antenna Analyzers or even a sensitive SWR meter with a QRP rig als long as the resistors don't get to hot.
I think that a Vector Network analyser or simple Antenna analyser is probably best.


I got some ferrite also from an other manufacturer called "fair rite". This ferrite material happened to be very close to the material 43 spec.
It had less inductance when tested with my meter and came closer to the 8.8uH as specified by Amidon with 2 windings.
The result was that from 3 to 50 Mhz the curve was more or less the same return loss. But on 1.6 Mhz this core had slighly higher return loss.
So there might be a little difference between batches of material 43 ferrite.
If you want to take that out of the equation than you need to use a longer material 43 piece of ferrite to cover 160m.

The same is valid for the output balun. You could make a 4:1 balun with 4 of these cores and probably cover 160m as well.
I haven't got the cores, so I can't test it.
The 4 cores can still be fitted on the PCB if you mount two above two cores. But if you have space than a long one is probably better (less leakage inductance).

In the input circuit there is a trimmer capacitor to gnd.
That capacitor needs to be trimmed for flattest SWR over the whole range.
But there is an other approach possible you could also trim it for best VSWR over 1.6 to 30 Mhz and switch in an extra capacitor when you transmit on 50 Mhz.
That will give absolute super VSWR on the input circuit. But there is absolutely no need for that. I think it makes things more complicated because the VSWR is good enough any way.

In the attached picture you see on how to measure on the input and the output.
I have replaced the FET by its equivalent impedance's.
On the input the gate capacity to gnd. (note is the same as in application note except they use 1 x 240pf (which is the same as 2 x 480pf because for the load of the transformer they are in series).
In order to keep the inductance of the leads short I chose to solder 480pf to gnd for each gate fet, allowing us to do the measurements better.
On the output the output capacity to with an 6.25 Ohm output impedance to gnd (as per the phillips application note).

Note for all measurements I happen to have some silver mica caps. You can use also normal ceramic caps because in the final design they have to go any way.

73 Ron
A picture can say more than a thousand words....<br />Here is one... with some words in the picture....
A picture can say more than a thousand words....
Here is one... with some words in the picture....


Re: BLF177 solid state HF Linear Amplifier

Post by VK4DD » Wed Nov 11, 2009 12:48 pm

Hi Gents,

I think most hams have a license to experiment with ham radio gear but very few do....
That is a pity because you can learn a lot from your experiments, reading about it, doing measurements, making mistakes (you learn the most from this)....
and than hopefully in the end susses !

The idea about this posting is to give some help on what is needed to make the baluns from.
But firstly I need to correct something... In the picture (of the previous posting) you see 2:1 on the transformer.
The 2:1 is actually the winding ration and not the impedance transforming ratio.
A transformer with 1 primary winding and 2 secondary windings is a called a 4:1 balun or transformer.
I think I should have called this a 4:1 transformer but instead I wrote down the 2:1 which I must admit is a bit confusing :!:
As long as you do 1 primary winding and 2 secondary windings you got the picture what I done.
The primary winding (low impedance winding) is the winding which is connected to the FET. This consists of a brass tube and a shorting PCB on the other end connecting these brass tubes.
The secondary winding (high impedance winding) is the winding connected to the outside world. This is made by 2 windings inside the brass tube.
It is preferred to have Teflon Isolated wire. I used silver wire with a Teflon sleeve around it.
The thickest wire you can fit inside the balun is usually fine. (rule of thumb VK4DD :wink: ). What matters is that the losses are low and the thicker the wire the lower the loss especially on HF...
But to be complete I will attach an application note so you can have a look how others think about this topic....

I bought some brass tube from a shop specialized in model airplanes. That is what I use and the sizes happen to line up with the holes in the cores.
Amazing these model boat and airplane shops have a very broad range of brass so usually you will find the right size.

So that is my variation on the Phillips application note. You could experiment with this alternative or build it as per the original application note.
But the way how you measure and tune the ferrite is the same.

I am now going to look into if I can change the design a little and make the BLF147 work in this PCB.
This is a 28V FET also very good inter-mod specs and 50:1 VSWR. This would be a perfect for in the shack because I run all my amplifiers of 28V.
(this probably means I need 3 secondary windings instead of 2 secondary windings for the 48V FETS).

It's great to see we got now over a 1000 hits with this posting :D

73 Ron
VK4DD has a license to experiment with ham radio equipment :P
PDF on how to construct baluns
(208.92 KiB) Downloaded 620 times
Baluns and brass tube...<br />Not shown on the picture... but I use now PCB material to solder to the brass tube.
Baluns and brass tube...
Not shown on the picture... but I use now PCB material to solder to the brass tube.


Re: BLF177 solid state HF Linear Amplifier

Post by VK4DD » Wed Nov 11, 2009 5:26 pm

Hi Gents,

I have been comparing some FETS and in specifically the feed back capacity.
The lower the feedback capacity the flatter the gain characteristic and better stability of the FET on low frequencies.

If you compare the BLF177 with the MRF150 from Motorola they you notice immediately how much better the BLF177 is.
The Motorola MRF150 has similar input and output capacities ans the BLF177 not surprising because it similar voltage level and similar power level.
But the real difference is the inter-mod spec and the feedback capacity. Motorola calls this capacitor: Reverse transfer capacity while NXP (old Phillips) call this capac

MRF150 C reverse transfer = C feedback = 40pF :(
BLF177 C reverse transfer = C feedback = 14pF :D

The difference is clear. The BLF177 amp does not need gain compensation or difficult feedback circuits to keep the amp stable, while the Motorola MRF150 amp needs this!

The other difference is BLF177 has VSWR of 50:1 and the MRF150 has a max VSWR of 30:1.
It is the difference between chalk and cheese.
No wonder I am a big fan of NXP :wink:
For US$ 50 to 60 you can buy these BLF177 Fets so price of these FETS are also pretty good.

As far as the BLF147... it is not going to work in this circuit, it needs a different circuit like the one used in
the FT1000MP MK V. One of the best finals YEASU ever made. ICOM uses in the IC7700/7800 cheap Chinese Fets and later the MRF150 after lots
problems with their finals. Very expensive rigs but not always good value.

An other nice thing about the MK V is that the final can be run in class A, but the power is than reduced to 80W.
All in All yeasu designed a very conservative final for good IMD performance and stability. 200W out of 2 x BLF147 is nice and conservative design. Well done Yeasu.

A final needs to be clean. This means more than good harmonic suppression, it also means a nice a narrow signal on the band. Look for high suppression of IM3, IM5 and IM7 (distortion products)
when you buy a linear. The other advantage of such a clean signal is that all the Energy is in this narrow band, it is not spread out over 50 Khz but is is used in 3 Khz wide signal :idea:
The 2.5 to 3Khz base band signal that is the signal you want to transmit, not all the rubbish around it. Rigs with bad ALC control and bad solid state and tube amps, in combination with phase noise
make a big mess of our amateur bands :cry: Sot the idea is to see if it is possible to make something better (and cheaper) ....

73's Ron


Re: BLF177 solid state HF Linear Amplifier

Post by WB9YYS » Wed Sep 29, 2010 11:27 am

VK3XIL wrote:Hi

Communications Concepts have a similar product


I e-mailed RF Power Systems to quote an approximate price on their 600 watt power combiner/splitter. They declined to quote a cost and suggested I get in touch with their distributor. The distributor turns out to be Communication Concepts and their website also excludes pricing info.


Re: BLF177 solid state HF Linear Amplifier

Post by KB1GMX » Thu Jan 06, 2011 3:43 am

What I've not found for this or the 2m BLF278 (PA0V version) is your version of the schematics. The ap notes are helpful but not exactly what you built.

Also for the 6M BLF177 how critical is using the copper heat spreader rather than a very heafty aluminum heatsink?


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