144 MHZ and 432 MHZ AMP Gallery

[VK4DD]

Hi Gents,

Please upload a picture and a short description of your home brew tube amp or transistor amp here.
You can tell what you like about this amp and what you think can be improved...

73's Ron VK4DD

[VK4DD]

Hi Gents,

This is the amp from Ken N0GZ.
He made a separate box for the power supply and the amp.
This reduces the weight of the individual items. I noticed one complete amp including power supply is quite a heavy box...
Probably because all the aluminium and copper.

Congrats to Kenn NOGZ for getting his amp almost ready.

[VK4DD]

Continue N0GZ power supply.

Kenn did a beautiful job with his power supply as well.
It includes shunts to measure the current.
One shunt for each power output.
RF chockes to get rid of the noise in his power supply.

The power pole connectors on the back allows him to feed or the other amp.
Well done.

73 Ron VK4DD

[VK4DD]

Hi Gents,

I just got an email from a friend in PA country.
He is building a QRO amp for 2m with a Siemens tube.
Any way have a look how nice this is made.
The tube is rated 3.7kV and 1.1Amps.
Still some hams tend to increase this and tweak a bit more power out of these tubes.
I estimate that this tube will do 3 to 4kW SSB on 2m.
Ideal for MS and EME work, great stuff.

Cheers
Ron VK4DD

[VK2GOM]

Great picture - lovely build quality. I can almost smell the corona from here HI.

73 - Rob VK2GOM

[VK4DD]

Hi Gents,

Here are the pictures from N0GZ amp.
It is now finished and fully operational.
640W PEP and 600W CW.
Ken N0GZ writes the CW power is limited by the power supply 28V/40A.

Ken used 2 x BLF248 and the Wilkinson combiner boards from VK4DD.

I am pleased to see an other amp is finished.

Cheers
Ron VK4DD

[VK4DD]

Hi Gents,

Here is the fully commissioned 2m amp from VK4CRO.
This is a 330W 2m amp based on the SR401. The SR401 is made by polyfet and the input/output impedances are very close to an BLF248.
As such it can be used with these BLF248 boards.
The RF part has been tested in November 2008 (from the top of my head).
But now the box, the protection, coax relays, sequencer etc.. has all been put together.

It works like a dream. On the input circuit the extra ferrite one hole material 61, 3 turns trough the ferrite.
This improves the balance/to unbalcanced transformation. It also my increase the output of the amp, as the left and the rigft are now equally loaded.
It also increased the output power in this situation by 10%.
Previously this amp has been tested and gave 300W out. Which is good for a SR401.
With the modification on the input circuit the amp runs 330W out.

You can see that Ron VK4CRO made a very nice stainless steel enclosure.
(Ron is now retired, but used to be fitter mechanic, and that helps a great deal)

The relays are 12V each and are wired up in series, with a diode in reverse over each coil.
That seems to work well, and no extra 12V regulator was needed.
The SWR detector came from an old Pager transmitter and works well in this amp.
This was installed because we did not have the SWR sensor from the Wilkinson board.
I gave Ron also a little bit of a hand with wiring up the protection and the sequencer.
But the credit for this project definitely goes to Ron VK4CRO.

Well done Ron VK4CRO.

Ron is now considering building a switched mode power supply into the box, and possibly an SWR meter on the front.

He just put an order in for a 2m Elecraft Transverter for his K3.
I am positive we will hear more from Ron once he is on the air.

Can't wait to see the next amp in this gallery.

73 Ron
VK4DD

[VK4DD]

Hi Gents,

Just got hold of the latest pics from Ron VK4CRO his amp. Output max 330W on 144 Mhz with 15W drive.
It has the Fans now fitted and the last changes have been made.
A little bit of alignment on the SWR protection LED and all that.
The fans are 2 x 12V and run when the amp is on. They have an 16 Ohm resistor 10W in series to drop the voltage a bit.
This reduces the noise and two fans are more than adequate. In fact one Fan would have been fine too.
The big fans run remarkably quiet, I think that this is probably an advantage of using big fans.

According to Ron the box is a bit big, but it has enough space to build in an 28V switch mode power supply or build an other 300W module in.
So plenty of space for the future.

I also like the finish of this amp. The XYL said it would even look good in the kitchen
No honestly it is a very nice box. It is quite difficult to make this out of stainless steel.
An the quality round the edges is excellent. I am impressed.

Good stuff Ron VK4CRO

Congratulations on finishing this project.

Ron VK4DD

[VK4DD]

Hi Gents,

More and more amps are being finished, as such this will certainly not be the last one we will see.....
This amp from John VK4MJF Amplifier uses also a single SR401 (alternative for a BLF248) just like the one from VK4CRO.
John made his own box from stainless steel and cut it with a laser cutter... So that's real high tech . It was the very same laser which also made the box from VK4CRO.
John was making the boxes with the laser, while VK4CRO was making and organizing other things. Real team work from the VK4WIE club.
Any way real nice laser technology and even the holes for the N-connector, the Fan, the Switches... they were all made by the laser. Nice!
No more drilling was needed. Except off course a few holes in the heat sink and the copper heat spreader.
This box is more compact than the one from VK4CRO. And believe it or not it just happened to be the same width as my favorite FT225RD (with Mutek front end).
I like this setup !

Looks great. Nice Job John !
John had some assistance from VK4DD with the electronics... and that speeded things up.
Any way good to see an other amp going over the finish line. Congratulations John VK4MJF.

Coax relays...
A Tothsu CX140D was used. I received an email from VK3 that these relays have some problems and arcing can occur where you solder the coax.
I have used semi rigid with a telfon core and I have removed the flux with some a special flux cleaner.
When solder flux is around in a strong RF field arcing occurs much quicker than when the surface is nice and clean.
The clearances are real small, as such it would have been better to use a different type or relay.
I guess none of us was aware of this issue. But it is good to pass this on to others... who can learn from this.

The results in VK as far as amps build (other amps finished outside VK are not included in this score).
VK4BG has build 3, My amp, VK4CRO, VK4MJF. I think the score for Queensland is now 6 amps finished, so far none from the other states in VK.
I think that is one of the reasons why VK4 is called the Amplifier state .
I would be good to know which state comes next, VK2, VK5 or VK3 ??? I have got no idea.
But I am sure they are all working hard on it and we will see more of it. (please do not respond to this topic about the coax relay).

Specs...
Last but not least this Amp gave 380Watts on the bird meter. If I push it real hard (not good causes splatter) than 400W can be achieved.
The power supply I used had enough grunt to supply 2 or 3 of these. So this amp is not limited by the power supply.
For SSB it does 350W real easy.
Just for the sake of using round numbers the name plate indicates 400W

I am sure we will hear more of John VK4MJF when he gets his power supply organized....

Greetings.
Ron
VK4DD

[VK4DD]

Hi Gents,

You probably want to see how the outside looks...
Well here are the pics from VK4MJF 2m amp on the outside.

The left red led indicates that the power is on. (I would have chosen an other color, like green or blue).
The led in the middle indicates that the SWR is high. It lights up bright when SWR is 2. But at SWR 1:1.5 it starts to glow weak.
A coupler was cut out from an other experiment PCB we had available here. Those who have the Wilkinson board don't need to worry about this, because it has got one the board.

The switch on the left is in series with the PTT. So if it is down, the amp starts to transmit when the transmitter is keyed.
If the switch is up, than the transmitted signal will bypass the amp via de coax relays, using the same path what is used for RX.

73 Ron
VK4DD

[VK4DD]

Hi Gents,

Congratulations to Karl VK2GKA has got his amplifier going with the BLF248. He received his FET last week and a couple of days later I received an email.

Hi Ron,
It’s working!!!!

Drawing 17A@27Volts and 15W drive.Output around 275W without
optimizing anything…. Very cool with the 3 fans…

Attaching Photo
73’ Karl VK2GKA

Later it appeared that the was driving the amp with 10W only.
When he corrected this he got 320W out with 15W drive. Than he started to optimize and moved C6 a little and got 350W out.
So that is a simlar result other have got including me for the green BLF boards.
Karl has also measured the Harmonics and noticed that the Harmonics level out was better than what he drove the amplifier.

Here are his measurements.

Measured levels:

Output 350W now.

288Mhz 432Mhz 576Mhz
-35dB -52dB -60dB PA input
-45dB -60dB -60dB PA output

All levels in reference to 144Mhz
Actually looks pretty good and makes the IC 206 look better after the amp….
73 Karl VK2GKA
Karl

I suggested to Karl to improve driver to use a 1/4 wave stub on the driver
(this will improve the second harmonic from the rig driving the amplifier).

Any way good to see the first VK2 getting the BLF248 to work.
According to Karl it was quite easy to get it going.
Amazing how much power you can get out of such a small FET..

Power supply...At the moment Karl is using 2 x 13.8V power supplies in series.
(one power supply modified to be above gnd).

Karl thinks he is going to use only 2 fans. Because it runs so cool...

73 Ron
VK4DD

[VK4DD]

Hi Gents,

Here are the latest pics from Karl VK2GKA. Karl worked hard to finish his PA within a week.
Showing us that this is not a mega project, but something what can be done quickly.
He ordered his switch mode power supply from computronics and paid Aud$ 15 for shipping.
http://www.computronics.com.au/meanwell/psp-600/
I think he actually enjoyed building this project, because he kept going and going. Nothing could stop him....
He really got the hang of it when he saw the watt meter going to the end of the scale.

Karl is still looking for a power/ reflecto meter with roughly the same size as his Amp meter.
Perhaps there are hams out there who have spare instrument out of an SWR meter?
Please email Karl VK2GKA kahamer (at) bigpond.net.au direct if you can help him out.

I normally install a ferrite clamp between the power supply and the PA. This is is better for the switcher, because you don't want the RF into the supply.
Other suggestion is to spread out the windings on the 35 Output coax. (a short in the windings is not good, the outer conductor carries RF)
For that reason it is better to change the Iron powder core to a Material 61 core.
If there are no problems with RF into other gear... well no big drama leave it in.

Install protection with a thyristor. But all these things take time, and you can expect to finish that in 1 week...
Even dough the fet is rated SWR 50:1. It is rated for a short time only. (how long is not specified in the data sheet).
All in all I think this is a very nice lay out. Congratulations. I like the way you have done your coax relays.
(I think CX-520 from Tothsu) Thank you for sharing these pictures with us.

I don't need the noisy 4cx250 amp any more, it is so nice and quiet in the shack and no more delays...
I got now more power and less noise.... In the past I missed contacts because usually the other party was gone when my 3 minute filament warm up time was over.
Now I just got instant power when I need it. Its great I love it. I am also very pleased with the power supply, it has got a remote on/off and I hear no noise on HF.
It is quite a good supply for the money. But that is not all ... I also Australian warranty also on it.
Karl VK2GKA

You are certainly together with VK4BG one of the rapid PA builders here in VK.

His amp is now on the air... and hopefully we will get some good inversions in the morning and your signal will come trough.
Other than that, Karl is planning to install a second yagi and add an other 3dB.
Together with the amp up grade will improve his station by 6dB. I am pretty sure that this will make a difference.

73
Ron
VK4DD

[VK4DD]

Hi Gents,

I was just going trough my old emails... deleting them one by one.
And then I found this one about the pigs... I am sure many of us will remember this email on the VHF reflector.

29 july 2008:
G'day,

Ron I am not questioning your skill as a power amplifier designer , however as a professional ditto for many years I know that there is many a slip twixt the cup and the lip and therefore I am not about to buy a pig in a poke. The poke must be opened and the pig allowed to run free for all to see. If this is not done --- no sale !

There you go already,

Gordon VK3ACC.

Good old memories from VK3ACC..

Well the truth was I had never designed an amp with a FET... so he should have questioned these skills...
But logic, care full steps, measuring and old techniques I used with tubes... but above all common sense.
Resulted in a great project. I certainly learned heaps.. out of this project.

The poke must be opened and the pig allowed to run free for all to see.

Yes .. Right here it is for all to see..

73 Ron
VK4DD

[VK4DD]

Hi Gents,

Here is an update on the VK4CRO amp and the VK4MJF amp.
After many hours operating some faults have developed.

Firstly we got problems with the Small Tohsu CX-140D relays on the output of the PA.
Apparently 300W SSB is more than they are can take, and as such a bigger relay was installed to overcome this problem.

Second issue was false trips.
Firstly I used shielded cable from the Coupler to the W6PQL pcb. That helped a great deal, but we still saw the red light flickering.
Than I removed the SWR sensor wire from the PCB and it red SWR led was still triggered.
As such the problem was diagnosed quickly. We were getting RF into the sequencer PCB because it was not shielded.
Instead of shielding it like in my amp with feed trough caps a different approach was used.
A few additonal 1nF SMD capacitors fixed the problem quickly.
See attached picture how and were we placed the 1nF SMD caps (marked by the red squares in the picture) to fix this problem.

The RF was picked up by the wiring, as such we choose to decouple most wires also the ones to the coax relay and the solid state (fet switch).
But most sensitive for RF was the LED circuit with the red led, which was direct connected to the trip circuit.
That was the most likely cause for RF getting into the sequencer.

Posted in the interest of sharing this solution with others.

John VK4MJF also reported the same issues, and his amp was changed accordingly with same good results.

From Karl VK2GKA I have heard that he is still happy with his amp. He loves it because it runs so cool, and always plenty power and is very quiet compared with his old 4cx250 amp.
Karl is planning to move, as such the planned antenna upgrade is not going to happen on this QTH. The antenna (farm) will be reviewed when he moves to a new QTH.
We keep our fingers crossed that your new QTH will be just as good as your old one Karl, but that is almost impossible with such a good location.

73 Ron
VK4DD

[VK4DD]

Hi All,

(this topic can be best viewed if you click here.
This will put the two postings behind each other).
viewtopic.php?t=8285&start=14

Ron VK4CRO has updated his amp. He says the amp has been improving.
The smaller Tohsu relays caused problems mainly because of limit power switching capability.
We have heard this before from VK3 and learned this lesson now as well

Any way the relays have been exchanged and we choose to use 1 relay in combination with a 2 coax connection to the transverter.
In that way we would need only one coax relay and a preamp could be installed with out having to worry about sequencers etc.
Other than that it saves also 1 relay

The Amplifier protection board was upgraded to the latest version, and the old board was given to Mick VK4NE to keep the cost down for his amp.
The solid state switch was removed because we had issues to interface it with Jims new PCB.
Apparently all the signals are low active. And the solid state switch we have needs a high active signal.

Initially we also had false trips due to the fact that the SWR pick up cable was not screened and it picked up pulses from the coax relay.
As such we used a thin coax cable for the reverse power sensor and used a diode over the coax relay coil.
Any way that solved the issues of false trips.
We also learned the hard way that we could not use a red led with a build in resistor.
That caused the trip circuit not to work properly.

But now all is well, so that is good.

Adjusting the max VSWR was easy after we used a 1/4 35 Ohm coax to create a VSWR of 2:1
Initially we tried to adjust it to 50W into a not connected antenna, but that was impossible.
The alternative would be to use a T section with with on one end a dummy load and on the other end an antenna.
That would also create a VSWR of 2:1. The amp is than set to trip at half power level.

Last but not least a first step was made to get the amp connected up to a display.
A picaxe monitor PCB was build in and wired up to a analog meter, using the PEP hold amplifier of this PCB only.

Some wiring changes were made to make it look neater.
And last but not least a piece of ferrite rod was build in to ensure no noise from the switched mode power supply would be radiated by the power lead

Nice to see the amp of Ron VK4CRO going trough an evolution.
Starting off with no power supply, than power supply build into the amp, later mains filters added, and now also power indicator added.
Last but not least the latest Jim W6PQL protection PCB which locks out the amp for bad VSWR.

Cheers
Ron
VK4DD

[VK4DD]

Hi Gents,

More pics added to previous posting.
Follow link to see main posting belonging to these pics
viewtopic.php?t=8285&start=14

73 Ron

[VK4DD]

Hi Gents,

More and more hams get on the air with their home brew amps. This is not the first BLF248 PA and certainly not the last one either.

The VK4NE PA is also completed. Mick will be on the air this Friday 4 Sept 2009 in the evening. He gets upto 390W out (FM carrier on 2m).
I suggested to do 300W max FM. In SSB there is less stress on the Fet with 390W.
Efficiency peaks at 72% @ 390W out !

It is a very compact amp and 390W is serious power on 2m. Mick has an excellent take off (north and south) from Brisbane so I am pretty sure the VK2's will notice a big signal during Aircraft scatter in the mornings and evenings. VK4NE, VK4CRO and VK4MJF are all quite active from about 19.00 hrs to 20.00 hrs on 144.200 in the evening.

VK4MJF cut the stainless for Mick with a laser. And Mick Mick VK4NE is a specialist in welding stainless steel, aluminum you name it.
He also build a lot of antennas. But this was a new experience.

Cheers
Ron
VK4DD

[VK4DD]

Hi Gents,

Here is a picture I got from Laurent F8DHB. He is building a 2m PA using a module from I0JXX.
You also see a sequencer PCB from Jim W6PQL and a Picaxe Station Monitor PCB from VK4DD.
He also uses the VK4DD GLCD display to read Power, Volts amps and temperature for remote controlling the amp.
He can switch the amp into standby mode with the GLCD and read out VSWR trips and a few other alarms.

There a so many options these days to make your own gear.
Laurent reported that he had the GLCD working a day after he received the parts in the mail.
Than we had some communication problems with the PICAXE/Station monitor PCB but that was because the software was not loaded
in the picaxe for the GLCD. And now he reports that it works on the bench.

Thanks Laurent for emailing me this picture.

73 Ron
VK4DD