300W BLF278 PA 48V (PA0V Nanko)

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Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Sat May 23, 2009 6:20 am

Hi Gents,

Ok well here is my solution for the 4:1 coax on the output circuit.

(see also calculating mean Z from previous posting....)

Phillipe F1HQM about coax. Can I use RG142?
While RG142 is specified to handle 2400W on 100 Mhz it is certainly capable of handling a lot of power on 2m.
However the cable is not a semi rigid, and as such you will have trouble soldering the shield to the PCB and to the other cables.
The second problem is that you will get an air gap between the shield and the insulation.
As such the whole coax is sort of distorted.... I would not recommend to go that way.

If you don't have access to big flea markets where people sell the coax Nanko was showing, than I suggest to use my idea.

My idea is to use parallel 2 pieces of Sucoflex SM-141-35. That is 3.5mm semi rigid (hand formable) with an impedance of 35 Ohm.
This is actually quite ideal, as parallel it becomes an 17.5 Ohm coax.

On top of that layer as the second layer use a single layer of this same coax.

In the first layer the currents will be much higher as the impedance's are very low.
17.5 Ohm = 2 x 35 Ohm parallel is a perfect impedance to have here :D
(check the schematic of see one of the previous postings MRF151G data sheet).
The second layer the impedance are much higher.
As such the voltage will be higher and the currents lower.
Lower current means less heat. So a single layer is enough.
Other than that, I think 35 Ohm is a real good impedance to have here :D

If you buy 1 meter of this coax you will be able to get at least 9 pieces out.
Which means it is enough to build 2 of these PA modules.

I actually think this is quite a good solution.
I tried bending a few coaxes and it fits really nice on the PCB.
Will post some pictures later....

More to come on the coax... keep on reading...

73 Ron VK4DD
The VK4DD stepped impedance 4:1 matching network...
Patents pending :-D
Last edited by VK4DD on Fri Jun 05, 2009 1:03 pm, edited 4 times in total.


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Fri May 29, 2009 1:00 pm

Hi All,

Nanko PA0V emailed me the other day a picture from a Nokia surplus power meter he had for sale... (about 2kg)
Shipping to VK made it too expensive.

I really liked the Meter it self... :idea: so I asked him if he could scan the scale and email it to me.
I just happened to have an identical instrument, but with a voltmeter scale. So all I need to do is print it with my DYMO label printer and I have an adhesive scale :D
Stick on top of the existing scale, cut of the edges with a sharp knife.
And there is my cheap power meter... with Power and SWR scale.

If you want a 600W scale, you can put a multiplier above the scale or edit the number in paint....


An other option is to download software from the internet. And design your own scale.
I have downloaded this software, played hours with it, but never been successful making a good scale that fitted my meter with this software.

Watt meter from Nanko PA0V
Make your own watt meter with this scale...


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Sat May 30, 2009 3:51 pm

Hi Gents,

On the input I am using a coax 316 (teflon) it is 2.6 mm thick.
Because the input is low power, this material is ideal for the balanced to unbalanced balun.

The length for coax can be calculated with this formula.

F = Freq in Mhz
L= length in Meter
V=velocity factor (for Telfon coax 0.7)

A 1/4 wave length is

F = 144 Mhz
Teflon V= 0.7 (=70% velocity factor)

L = V x 300/(4 x F)
L = 0.7 x 300/(4 x144) = 0.365 meter. or 36.5 cm.

This is not the coax for the output, this is the little coax rolled up on the input circuit.

73 Ron


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Sat May 30, 2009 5:11 pm

Hi All,

I hoped to build this amp in one day..., but I got stuck when I run out of parts....
I decided that the amp was going to be for SSB only, as such I think it should be possible to mount the BLF278 direct on the aluminum.
The BLF278 is cheaper, so I am willing to take a little more risk in that perspective...

The base of the heat sink is almost 10mm thick and that helps also to spread out the heat.

Any way.. I you want to build it in a day, you don't want to start drilling and mounting copper etc.

I also used some ATC's on the input, which is not mandatory. But I had them in stock, so I decided to use them.
They are nice and small and I like to work with them.

I have used 35 Ohm coax for the output circuit.
The first layer has 2 x 35 Ohm coax parallel resulting in quite a bit of copper for the center conductor.. (that is the main thing).

I did some calculations and compared the center conductor of a 50 Ohm, 6mm teflon coax with the 35 Ohm center conductor.
And believe it or not, there is only 0.2 mm difference in thickness between these 2 cables.
However 2 x 35 Ohm center conductors has 75% more copper compared with a 6mm 50 Ohm center conductor.
So I believe that 35 Ohm solution will run cooler than the 6mm 50 Ohm coax.

The second layer is only 1 x 35 Ohm. That is because the impedance is higher and as such lower currents trough this piece of coax.

First I bended the coax in shape and stripped and bend the leads in position. Than I soldered the first two 35 Ohm coaxes (which are parallel) together from below.
I bended them again into shape. I tinned the PCB. And than soldered them to the board using two solder irons. I think you need at least one 80W Iron and a 40W iron.
Any thing less does not have enough heat. Soldering bit by bit, making sure it stays clear from the gnd.
I would not say that soldering these coaxes is an easy job.... there is not much room, but if you don't make a mistake, it will fit just fine.
The third coax on top was easy to solder. Connect the leads as shown in the picture.
All the shields are interconnected and soldered to the big "U" on the circuit board.

Any way have a look at the pictures...how it all worked out.

A few words about the coax...
Soldering the 2 x 35 Ohm cables is possible, but it is a bit of a challenge. If you can get the thick 6mm cable, go for it.
That would be easy to solder.

After soldering the coax, clean up the solder flux with alcohol or other special flux cleaner
(I used nail remover, very agressive and not optimal... but make sure it does not solve the green coating of the PCB).

But at the end of the day, I think it is going very well :D
It all seems to fit, and need to order some bits on Monday.
I need to chase these parts up in VK. No idea were I can get a big compression trimmer...

73 Ron
fuse view.JPG
The ATC is used as a pilar and a piece of copper is used as a bridge between the coax and the ATC.
You can't see the 1NF ATC, but it is there soldered to the GND.
Top view.JPG
This is the top view, some components still need to be mounted... like the trimmer capacitors.
Balun view.JPG
Here you can see how VK4DD made the balun on the PCB with UT141-35 (35 Ohm coax)
Last edited by VK4DD on Fri Jun 05, 2009 8:00 am, edited 2 times in total.


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Sun May 31, 2009 9:48 am

Hi Gents,

I received some questions about which heat sink I am using...

I buy my heat sink mostly from Ebay.
Seller: barrredboss

5 3/8 WIDE

I ask barrredboss to cut this heat sink for me ==> 10 inch long.

This is how it looks on his Ebay site...

You will also need a 120mm FAN to produce air across the heat sink.
This will give you this nice low heat resistance you are after.

73 Ron
Ebay Seller: barrredboss
5 3/8 WIDE


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Mon Jun 01, 2009 6:22 pm

Hi Gents,

Pino IK0SMG emailed me an interesting schematic he uses for the protection. It uses a thyristor for the protection.
I would like to use this idea to change the cicuit from W6PQL because I prefer to have a reset when a fault occurs.

The circuit I got from Pino uses a PNP transistor Q1 to interrupt the 12V to the coax relays.
Q2 activates the PTT and energizes the coax relays.
Different jumper settings for JP1 and JP2 are possible depending on how you activate the PTT circuit. (to GND or not)

The rectified voltage from the coupler should be just high enough in a fault situation to trip the Thyristor (SCR). One the Thyristor is tripped (actived) it will start to conduct and the LED (DL2 ALARM) will come up.
Coax relays and Transistor Q2 will be cut off from the +12V supply because Q1 has stopped conducting.
The coax relays will no longer be energized. The amp is tripped.

RV2 sets the level at which the Thyristor (SCR) trips. Some damping capacitors are on the gate of SCR to reduce false trips.
(note that some transmitters have very bad function of ALC and that they reduce very large power spikes when the power is reduced to several watts, the capacitor should not be increased
for this sort situations, because it makes the circuit too insensitive).

I think that Q1 should be an NPN, but that is probably because the drawing needs to be updated.

The standby/reset switch will have to be opened so that the Thyristor will no longer carry current.
It will stop conducting and the circuit is reset.

Ideas for further improvements by VK4DD

I think this is a good circuit, but I am going to make a few changes to it....
I would like to use a sold state relay or big FET to replace the function of RLY1.
This would cut of the current to the amplifier much quicker, which will allow the fet to live longer.
I would also like to double the trip circuit so that an input over drive circuit can be added as well.

Thank you very much Pino for emailing me this very good and simple Amplifier services schematic.
I am sure we are going to see more of Pino's work.


Continue to next page


Last edited by VK4DD on Sat Jun 06, 2009 6:54 am, edited 6 times in total.


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Thu Jun 04, 2009 1:02 pm

Hi Gents,

I got my BLF278 going 300W on 144 Mhz with 4.2W drive, but I made a few changes in the design, which I have documented in previous postings.
This is because I don't want to double up postings and create confusion. (I will write on a posting, which date it was updated...)

I drove the amp with 4.2W because that was full power from my little Icom hand held radio.
Half power gave from my HT is 1.8W. That was good for 240W out. The input VSWR is excellent, but I made some changes to get it down further.
The trimmer PA0V specified was to big. I found that the optimum was with the plates fully open (minimum capacity).
As such I changed the trimmer for a smaller one from only 20pF. This trimmer is now nearly at minimum capcity.
My guesstimate is that this capacity of is now in the order of 5 to 7pF. As such the 20pF trimmer is a better choice.

I also noticed that PA0V had a small capacitor in series with the coax. I think that was done to improve the VSWR, but there was no need for it in my case.
Perhaps because I used different and ATC caps on the input? perhaps because this is a different PCB?
When I drove the amp with 4.2W I could only just see the meter moving when I measured the reverse power.
As such reverse power is 30mw ? 50mW? too small to measure with a 10W bird slug.
This means that the return loss is about 20dB :D I did not even bother to further improve this.

Output circuit...

I had only a 4-50pF compression trimmer, so I decided to use it and have a 47pF ATC parallel.
The power was less at minimum capacity so I changed the 47pF ATC for a 68pF ATC and started tuning the compression trimmer again.
I could not find a sharp dip of peak... so I increased it to 100pF parallel on my compression trimmer.
That gave slightly less output, so I went back to just one ATC of 82pF, also tested 100pF, and even 200pF.

Best results: with 2 x 39pF ATC on the output.
One ATC can only just handle the 300W. But the 2 x 39pF is a better choice as it will also be capable of driving a VSWR of 2:1 load.

I got 9.8 Amp x 48V = 470W input, output was 300W on the bird.
300/470= 64% efficiency (bias was set to 0.2Amp each fet).
I think that is spot of what can be expected for a BLF278 on 144 Mhz.
My bird meter should be spot on, and my amp meter is a digital meter from Fluke.

Bias current

Firstly make sure the trimmer resistor is not set on maximum voltage to the BLF278...... that will give you 10Amp idle curerent or more... :shock:
I accidentally did this :roll: It is suggested to avoid this. I recommend to do first bias alignment with 3Amp fast fuse for this reason....

Class AB is recommended for SSB use:

For 144 Mhz you need to measure 0.9A. That means each fet gets 450mA (2 fets in one transistor). I suggest to setup your bias on a warm heat sink.

If you going to use it at WSJT/FM just set it at 0.4 Amp total (2 x 0.2A). that is enough.

It is clear that the lower the bias current, the higher the efficiency.
It is also clear that the higher the bias, the more linear the amp....
In SSB the amp needs to be linear so that is why the idle current is higher.

On the input I made a few minor changes, which I have noted under the material list in bold letters.
You can try both, and choose what is best for you. Lets us know what you did and what the results are.
(I am very happy with this input VSWR).

The amp appeared to be nice and stable, no funny things. Very good indeed.

Bias resistor...
I used a 510 Ohm/5W resistor and connected it to the 48V.
If you use 24V or 12V to switch your bias, just change the value.

But at the end of the day, I am a very happy chappy.
The BLF278 works like a rocket 8)

300W out, for very little money, that is excellent.

More goodies to come... I will make a posting on how to make an Harmonic filter, how to combine two amps.
I will also be happy to answer specific questions. Please feel free to email me these.

73 Ron

See the action pictures...
The bird meter proofs 300W out at 9.7 Amps/ 48VDC. Drive power 4.2W
Good to see that it works.

Bird meter fitted with 1000W slug.
Use lowest scale. 20 = 200W, 40 = 400W.
Picture of the input circuit, smaller trimmer capacitor and ATC used. With excellent return loss.
It is not a good idea to tune it with a metal screw driver. If you have no plastic, turn the amp off, move the postition, turn on and repeat procedure until optimal position found.
Last edited by VK4DD on Thu Jun 04, 2009 6:43 pm, edited 2 times in total.


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Thu Jun 04, 2009 3:04 pm

Hi Gents,

I have updated the parts list. See posting 3.
I have also updated other pages, to make them more accurate..please read all postings again :mrgreen:
I will attach a picture showing you how the compression trimmer is replaced by 2 x 39pF ATC.
This is not only a cheaper solution, it is a better solution also.
I have blown up many compression trimmers over the years, besides that, they can start to arc etc.
I just don't like these things in a final and will get rid of them if possible.

Attached is a picture showing you how I used these 3 islands (or dots on the PCB).
The ATC have a narrow and a wide side.
I soldered the ATC next to each other with the narrow side up.
This gives them more clearance from the gnd.

Here is more data on the amp.
400mW in gives 80W out.
1.8W in gives 240W out.
4.2W in (well into saturation level) gives 300W out.

No copper heat spreader was used. That seems to be fine for SSB work.
Modes like FM/WSJT will require a copper heat spreader. A fan will need to be used in combination with the heat sink to keep the amp cool.

35 Ohm SM141-35 coax.
After running it in the test, it was still only finger warm. Very good.

Gerd DJ5BV emailed me also that he is working on getting 35 Ohm real cheap.
But so far I am still waiting on him. I think he is planning to buy this stuff in bulk as other hams in Germany are also interested in it :D
Gerd told me he is using this 35 Ohm coax to match his DK7ZB 28 Ohm yagi. Any way it seems that the applications for the 35 Ohm coax have grown
steep after the BLF248 PA, the BLF278 PA. I hope to see one day 6mm 35 Ohm for sale by the meter as well ...

I noticed that http://www.rfmicrowave.it is also selling 25 Ohm coax. UT141-25.
This really close to the mean Z of 22.3 Ohm we calculated earlier.

The only disadvantage is price and the fact it is rigid. Semi rigid is ideal. But I am sure you can bend it... :wink:
It is 17 Euro per meter, but 1 meter is enough to build 3 amps... so that is less than 6 euro coax per amp.
This would also be the guy where you can purchase ATC's etc.
(apart from me off course... I got about 1500 ATC's size 100B, but not the complete range...., that is probably enough for my own experimental needs :D )

That is probably the easy way to build this amp. Only one coax of 25 Ohm on the bottom, and one coax of 25 Ohm on the top.
1 meter should be enough to build 3 of these amps.
That would make soldering the 4:1 balun into a piece of cake 8)



Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Fri Jun 05, 2009 2:10 pm

Hi Gents,

I have experimented a little bit more...
with a 39pF and a 27pf parallel I get 320W out at 10.5 Amps/48V.
That means the efficiency is 63.5 %
a little bit more, power efficiency only 0.5% less...

I don't recommend to get more power out of your BLF278, I think the 300W is already enough.

Next step would be to build an harmonic filter.

Well here is one..

http://www.dj9kw.de/dj9kw/projekte/afu/ ... owpass.htm

if you find etching difficult, or you have no access to pcb material than here is an other method to make the capacitors...
UT-141 coax has a capacity of approx 1pF per cm.
So 34pF is 34 cm.
It is best is you cut this into 2 pieces of 17 cm. Than connect the begin with the end so the coax is a loop.
Don't cut it to short try first with a longer piece and make sure you end up with the correct capacity.

You can solder the coax direct to blank (not etched) piece of FR4 PCB.

It is that easy.


73 Ron


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK5AYD » Fri Jun 05, 2009 9:54 pm

Good evening.....
I am looking at buying one of the devices from simpli_city212 on ebay.....am wondering if anyone has had problems with this supplier before I make a move......
Thanks for any comment......


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Sat Jun 06, 2009 7:26 am

Shipping with that guy is US$ 35... so your BLF278 will cost US$110 landed. No experience with this seller.
Suggest to contact VK3KAI, he bought 2 x BLF278 for this project via Ebay for US$85 each.
2 x BLF78 is a very conservative way to make 400W (legal limit VK) that would not stress the devices very much at all.

73 Ron

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Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK3PF » Sat Jun 06, 2009 1:21 pm

Hi all,

I bought my 2 devices from "subrata1979". US$170 for 2 devices plus US$40 for P&P for the pair (he normally charges US$30 for 1 device for P&P), so US$210 total. Took just over a week for the devices to arrive - very well packaged.

Now I just need time to chase all the info and to assemble the rest of the pieces, and start with the soldering iron!

Peter VK3KAI


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Sun Jun 07, 2009 6:33 am

Got an email from David VK5AYD, and am passing on the information:
I will have a couple BLF278 for resale ..if any one wants them...
I will also need some coax.

I am in Coober pedy grid square PG70JX and you want to get into Air craft /Tropo/Es.
I use an FT857 and 11 ELement yagi
David VK5AYD and Nora VK5NYD
David/Nora. Cooper pedy is probably one of the best 2m locations in VK to work all states.
It would also be interesting to know how the path is to VK6.
Let us know when your 2m station ready.

I am very pleased to see you building the amp, and I will sponsor some coax and ATC caps.
It will be great to see you on the air. You are exactly the sort of station people want to see on the air.

73 Ron

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Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK3PF » Sun Jun 07, 2009 10:52 am

Hi all,

Is anyone interested in a group buy of the BLF278?

I have received an email from the guy from whom I bought my 2 devices. He has a very interesting offer of 20 devices for USD1000, so only USD50 per FET! That would be about $65 per FET plus P&P within VK.

I can afford to spend that much, but I would need enough people to commit to purchasing the devices - I do not need any FETs, but am happy to facilitate others getting the devices.

Email me direct at vk3kai@wia.org.au

Peter VK3KAI


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Sun Jun 07, 2009 10:18 pm

Hi Gents,

I will supply 20 PCB's to a radio club in VK3 for 20 x 300W 2m PA. This club buys Fets and parts and offer a kit at a crazy $/watt ratio...that will never be matched again in VK.
Note this is not for export, but to promote more and better stations on the air in VK.
In order to promote 2m activity VK4DD has sponsored this with low prices and will do the same with other radio clubs who want to do these things in high volume.
Provided that the amps will be sold and used in VK. Well done Peter !

I am happy to do this also with other radio clubs, in order to make home brew more popular.

73 Ron
Last edited by VK4DD on Tue Jun 23, 2009 6:20 pm, edited 4 times in total.


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Tue Jun 23, 2009 6:11 pm

Hi All,

I have completed the schematic from the BLF278 PA.
If there is an update, than I will modify this posting and upload it here.
except the revision date below will be changed.
One location will avoid confusion in this matter.

Please down load it here. (I will update this posting)

SCHEMATIC CORRECTED 29 July 2009 necessary revision: had input coax feeding on wrong point. Was shown correct in pics but not in schematic.
Also updated some resistor values for R2 to reduce stress on R3

SCHEMATIC CORRECTED 24 Sept 2009 necessary revision: had C6 shown as 39pf. This was a copy and paste error in the schematic. Now corrected to show correct value C6 is 120pF.
Thanks to Nico PE0NYJ for picking up this error
(important update)

73 Ron
Corrected version 24 Sept 2009.
C6 had incorrect value. Now updated to show 120pF.
Last edited by VK4DD on Thu Sep 24, 2009 8:41 am, edited 18 times in total.

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Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK3PF » Tue Jun 23, 2009 8:29 pm

Hello all,

As Ron has indicated, EZARC has decided to support a kit project for the BLF278 144 MHz amplifier.

20 FETs have been ordered & paid, also pcb boards at a good price (thanks Ron). As a first step, we need to wait to see what the Tax man wants when the FETs arrive, HI!

I need to work out what else is feasible to include in a short form kit, including suitable cable for the output balun (?25 ohm). BUT work is hectic at present (lots of exam papers to mark!!). One possibility we will examine is to include a decent heatsink, possibly source in VK3. I hope that the supplier might do a deal for a bulk order of 20 or more units - prices look OK at present, based on web published RRP - certainly comparable with an eBay seller once P&P costs are included, even if buying 4 units per deal. So a possible kit may be:
FET, pcb, coax for output balun, SMDs, heatsink, maybe the other on-board bits.

What else would you need (without having checked Ron's earlier posting)?
Copper heat spreader, input & output coax leads, monitoring circuit & bits, change over relays, misc. hardware, etc.

I hope to have details available in the next week or so, so either wait for a further announcement here, or drop me an email with your potential requirements.

There were several members of the club interested (around half the FETs), so they will get first bite at the cherry, as it were..... I am sure that everyone will appreciate that club members get first option, if the club is backing the deal/s. If there are extra units available, they will be announced here.

So.... more news soon.


Peter VK3KAI


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Sat Jun 27, 2009 1:54 pm

Hi Gents,

Looks like there will be a lot of home brew activity in VK3 and that is excellent news.
Thank you for this great initiative Peter. I look forward hearing more DX from down south.
This will also boost the Es contacts during summer. This is my personal experience as well as the experience from Ken N0GZ who had the opportunity to run this summer with his 2 x BLF248 amp in the USA.
But I suppose that is an other topic, which I don't want to discuss here.

I have done some work to on how to combine these BLF278 (and other ) amps.
On my home page I run also a small forum, just to document lots of info including combiners, where to get coax cheaper etc etc.

I have one combiner in particular in mind for this project and that is this one.
It is a hybrid combiner, partially Wilkinson and partially a quadrature combiner.
Basically it is a Wilkinson combiner with 2 90 degrees delay lines. This has the advantage that less power disappears because the PA impedance's don't interact with each other.

Any way here you can find more about this topic and other combiners.
http://www.vk4dd.com/forum/viewtopic.ph ... 5&start=10

I have also uploaded the schematic on how you do this.

Please note that you can pieces of coax on the input and the output, to go to these
combiners as long as you keep the length the same.

Other than that keep also an eye on the Page of Jim W6PQL. Jim will release a DC solid state switch for 48V.
This will be good if you want to protect the amp of a bad VSWR.

This will work also with his all new amplifier protection PCB.


73 Ron
2 port Wilkinson.PNG


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Wed Jul 01, 2009 10:55 pm

Hi Gents,

I got some PCB's developed which could be useful for this project.
A coupler...
A power supply to drop down 40V to 24V or 12V(...as long as you don't do more than 100W dissipation)
New station monitor PCB's. This is useful because normal 78XX voltage regulator have limited current capacity
or can only dissipate a few watts.

More info here.

http://www.vk4dd.com/forum/viewtopic.ph ... 1&p=84#p84

73 Ron
Coupler 2m.PNG
Power supply.JPG
Updated 10 July. 78XX regulators max 40V in
(or specified differently in data sheet).
Last edited by VK4DD on Fri Jul 10, 2009 8:32 pm, edited 2 times in total.


Re: 300W BLF278 PA 48V (PA0V Nanko)

Post by VK4DD » Sun Jul 05, 2009 1:30 pm

Hi Gents,

Jim W6PQL will have soon 50V Fet switches.
Ask Jim also for his 50 Amp switches they are $1 extra and certainly worth the extra dollar !!

But here is an other option that worked well with the first generation boards from Jim.
Not the second generation because he has got two active low signals.
Kill (when the SWR is high)
and the sequencer. I suppose an extra interface around the solid state could solve this.
But you have to make your own.

Any way here are these so called DC solid state relays.
I found them here also for 100V/40Amp
More than enough for a 2 x BLF278.

SSRDC100V40A SPST 0-100Vdc 40A DC Solid State Relay Yes 1 US$19.90
That is more than half the price from our Jaycar stores in VK.

73 Ron
HFS33_150.jpg (34.47 KiB) Viewed 5203 times
Last edited by VK4DD on Sat Sep 05, 2009 11:36 am, edited 1 time in total.

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