Make the Micro PA-50 work for you!

/ voiceovertrails
Watch to find out how I fixed the SWR issue on this amp. This little amplifier shuts down any time the SWR exceeds about 1.5:1. There's a relatively easy fix if you're experienced with a soldering iron.
Should you buy the Micro PA-50? This little amp is all over Aliexpress and it seems like it might be the perfect amp to hook up to your qrp rig. If it works, it could improve the utility of your IC-705, FT-817, KX-2, KX-3, etc..

[@jonhult5027]

Great work! Mine arrives tomorrow and looking forward to making the mod. I did read the article you mentioned even before your video and was expecting to solder to the smaller resistor. Glad you found a better alternative. Previously trained in SMD soldering so it should be a breeze. Thumbs up!

[@KD7QOW-np9gd]

Thanks!

[@jakelarson9935]

I added the 10k resistor to fix the SWR circuit and it seems to work perfectly. I highly recommend while your'e in there to pull that buzzer out and replace it with an LED. I also added a relay in parallel with the FN switch hooked up to a Pi with Node Red so when I'm operating my IC-705 remotely I can "press" the button to reset the error or "long press" to turn the PA on and off.

[@cWatts-zv3oo]

Are you using a half or quarter watt resistor?

[@jakelarson9935]

@@cWatts-zv3oo Think I used a 1/8W. I don't think it really matters as it's not really handling any current.

[@cWatts-zv3oo]

@jakelarson9935 thanks man. Is the amp still performing well for you?

[@Lowell-W8ISM]

Thanks for video. Worked great for awhile, then started having intermittent problems. Did your 33 ohm resistor fix and also ran a better ground to the amp. Seems to be working okay now - fingers crossed. Subscribed. Keep up the good work! Update: It died. I was messing around with an accessory cable from the X6100 which worked fine at first, and then bam! SWR reads greater than 3 and immediately alarms - even in auto mode. Oh well. This thing had potential, and it worked great for awhile.

[@KD7QOW-np9gd]

Keep ‘em crossed! I got overzealous and blew mine up when I turned off the protection. Replacing the finals didn’t fix it. In a drawer it sits.

[@mike94560]

Connection chain. Antenna -> ATU -> Amp -> Rig. Bypass amp (long press on Amp button) until you tune up with just the rig. Then turn on Amp. Another important tip. The RF output drops with supply voltage. I run mine at 9 volts and get 25W out on 20m. If I run it at 13.8V it puts out 52+ watts and shuts off. My rig does not have RF output level adjust. So I just dropped the voltage to the Amp and it works fine. Less heat, longer life, etc. Works for me with no mods.

[@KD7QOW-np9gd]

That’s an interesting approach. Totally works if you have a variable power supply.

[@W5BL]

Great work! I went ahead and pulled the trigger on one. I run a Chameleon Magnetic Loop antenna so i have to get extremely precise tuning before transmitting. This will (theoretically) bump up my 705’s signal about 1 S-unit. Will be fun either way. 73’s W5BL

[@KD7QOW-np9gd]

It’s definitely a project! The nice part is if you blow up the finals the replacement transistors are dirt cheap!

[@W5BL]

@@KD7QOW-np9gdso today I successfully performed the great “SlugJob” of ‘23. Used the same resistor you did and I can report it is working flawlessly. The weird part is that it reads an swr of 1.0 no matter what band, no matter what frequency I transmit on. I mean I’m definitely not complaining but it’s kinda funny Bc I know it’s gotta be higher than that at places. I’ve only played with it a little bit but this operation completely changes this cool little PA for the Icom 705. Thanks again and 73’s.

[@W5BL]

@@deerae7460 yeah I must have fried the swr reader circuit is only thing I can think of. Literally the only thing that trips it now is feeding it too much power. Which is a good thing. I like the mod a whole lot! It’s a functional little amp now.

[@AlbertLiberman-ch7vj]

Working solution: I wound 3 turns from the input transformer windings and flashed firmware v1.5-beta. The author has changed the algorithm for calculating power and SWR. Now the amplifier shows SWR 1:1.2 with real 1:1.1, and no longer jumps like a mad deer. I did not put an additional resistor. I was already thinking of launching this amp into the river ))

[@KD7QOW-np9gd]

Fine Business! I blew up the finals on mine, tried replacing them, and they blew up again. I haven’t had the time or patience to figure out what’s going on and sort of lost interest at this point. But it’s good to hear the designer of the amp has fixed the problem!

[@user-or1xo7nx6h]

Where do I find the manual?

[@barrykery1175]

Good informative video. It's an interesting little amp. Thanks for the SWR resistor mod. Did you hook up the PTT line from the 705 to the amp? Barry, KU3X

[@KD7QOW-np9gd]

I tried the ptt line and it did nothing, even with the amp in icom mode.

[@brianfields4479]

Can anyone advise me of a better fan to use, as mine is so noisey, I cannot hear the rx, even with phones on.

[@KD7QOW-np9gd]

I noticed the fan is way less obnoxious outside. Before I blew up the finals, I found this amp to be completely unusable inside because of the fan noise.

[@godfreydebouillon8807]

Bought the PA50+ for XIEGU g90. Anyone know what chord is needed for the ACC Port?

[@KD7QOW-np9gd]

I tried a 3.5mm TRS and it didn't work. Not sure if that port actually does anything.

[@bigshafe]

Thanks for information. I'm not very electrically inclined but I've heard about a relay input from the 705 to protect it? Is that a concern with this amp?

[@KD7QOW-np9gd]

It’s not a concern if you just use the RF sense and don’t hook up a control cable. I never got the control cable to work anyway, so it’s not something I’d worry about. Honestly, I wouldn’t buy this amp unless you’re electrically inclined and you like working on stuff. I’ve blown out two sets of finals on mine and it just sits in a drawer now.

[@bigshafe]

@@KD7QOW-np9gd thanks for the info. Soldering and working on stuff isn't a problem for me, just the electrical stuff. I'm more mechanically inclined. Thanks for the videos.

[@greene_hu]

What a good idea! So You just lowered the resistance by 30 ohms, and that's it?

[@KD7QOW-np9gd]

That's it! It's not the most elegant solution, but it's effective.

[@russlee130]

with mine after many hours of deliberation and much trial and error i firstly connected a 1.1 balun to my ic 705 and that knocked the swr down, then i unplugged the fan and Bingo swr 1.00 but at 40 watts it gets hot quickly so i tried many options and 30 to 32 watts max it now runs ft8 all day and the temp never goes above 45deg , the fan in my opinion is causing the swr mismatch

[@KD7QOW-np9gd]

Huh. That's interesting and I would never have guessed. Can't argue with success, though. Glad you found a solution!

[@russlee130]

There has been a change since I did this. I have added a new sunon 60mm silent fan to the top of the unit after drilling many small holes . Only when I place a fan to the back of the unit close to the input and output does the SWR rise. This is why I love radio 😂

[@philipwells2793]

Do you know the current draw @50w and on receive?

[@KD7QOW-np9gd]

I've never measured it, but I've run 100 watts SSB with a 6 AH battery for multiple activations and not had a problem.

[@user-or1xo7nx6h]

No manual came with mine. Where do I get one?

[@KD7QOW-np9gd]

Great question! I have no idea!!!

[@KD7QOW-np9gd]

@@ScottGibson178 Tried it. Only found some directions on their ebay posting.

[@Philip-KA4KOE]

Where did you get this amp?

[@KD7QOW-np9gd]

Aliexpress.

[@ronlewkowicz9656]

Well, I didn't do this mod as I don't have an SWR issue and I never disabled the protection mode as protection seems like a good idea. Regardless after about 3 months the amp went to a dead short. Customer service told me the finals were damaged and gave me the go ahead to replace them. I ordered a bunch since they are cheap and put in a new pair. Short was fixed so hooked it back up. As soon as the power supply was switched on the amp went to dead short again. Tried another new pair, same result. So it seems something in these blows that then causes cascade failure or the IRF530. Anyway I haven't been able to fix it and won't be buying another.

[@KD7QOW-np9gd]

Yeah, mine blows finals now too. I don’t want to take the time to figure out why so it’s sitting in a drawer.

[@M0UAW_IO83]

Given these things use switching FETs which are designed to turn full on rather than have a nice linear behaviour I'd probably want to wind down the gate bias voltage all the way before powering it back up after replacing them or they'll let the magic smoke out easily. @@KD7QOW-np9gd

[@mrtechie6810]

So you would not recommend this amp? I'm thinking of getting the Hermes Lite 2, which is 5W maximum output.

[@ronlewkowicz9656]

@@mrtechie6810 I guess the answer would be it depends. I'm still not sure why mine blew up. Sure I accidentally forgot to switch the tuner once or twice and hit the SWR protection shut off and leaned in a little too close to the mic a few times and hit the high power protection shut off, but I assume that is what the protection is for. Lot's of people run these without issue. The developer has setup a private facebook group now so you can actually contact him and get assistance, get new firmware and so on. So some issues are now fixed in firmware and other improvements to hardware made in a new PA50+ model. If you can be very careful maybe it won't blow up. If you want to use this outdoor for POTA, SOTA probably worth looking at. In the shack I found the fan noise to be very, very loud and for this reason would be enough on it's own to not buy another.

[@ronlewkowicz9656]

@@mrtechie6810 BTW I highly recommend the Hermes Lite 2.

[@bloguetronica]

However, the main reason is, why buying an IC-705, when you can buy a Yaesu FT-891 which offers good value for the money? That amplifier can't really hold producing 50W. However, it is great for testing contacts in QRP mode.

[@KD7QOW-np9gd]

Totally agree! In fact, I just carry my FT-891 to summits and it's less hassle than trying to carry this thing.

[@bloguetronica]

@@KD7QOW-np9gd Indeed. Less components to carry, and the FT-891 does 100 W easily and it is very forgiving. I have that radio myself and I just love it.

[@jensspiess3239]

Mine amplifiere has operating point >> C-operation

[@KD7QOW-np9gd]

I think their quality control is very inconsistent. Some people are getting working units with no problems while others are getting a box of gremlins.

[@TheMicrofox]

Why does someone design a PA that stops working at 28.5 MHz instead of 30 MHz. That's complete nonsense.

[@KD7QOW-np9gd]

Because the person who “designed” this didn’t know a lot about RF design. They just added a programmable chip and a display to an existing analog design that was never intended for this purpose.

[@KD7QOW-np9gd]

@@wdycsqcsqwdy If I was going to design an amplifier, I'd design one that works as advertised or else I wouldn't put it up for sale! Why can't you just admit that this product has serious problems and then fix it? Do you really think we're all just stupid?

[@germanjohn5626]

Defeating a safety feature....not smart.

[@CPLBSS88]

let me guess, you also go exactly 1 mph under the speed limit, and are a proud card holder of the "lowest common denominator" club? 😂

[@KD7QOW-np9gd]

Which transistors did you replace them with? I think this would be a great candidate for some robust transistors.

[@ra4fkz377]

@@KD7QOW-np9gd Тоже сгорели выходные транзисторы, работали неустойчиво, сигнал на пиках был рваный. Буду менять на другие транзисторы - IRLZ24N.