Make the Micro PA-50 work for you!

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..

[jakelarson]

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.

[jonhult]

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!

[mike]

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.

[Lowell-WISM]

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.

[WBL]

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

[AlbertLiberman-chvj]

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 ))

[barrykery]

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

[greene_hu]

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

[ronlewkowicz]

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.

[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?

[russlee]

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

[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.

[godfreydebouillon]

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

[brianfields]

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

[philipwells]

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

[KLXY-kp]

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

[jensspiess]

Mine amplifiere has operating point >> C-operation << and works complete NOT linear !!! It can not used for SSB . SSB-signal and also CW signal comes out with complete destroyd and distorsions This amplifiere is made for rubbish, maybe the one which I got delivered ...

[TheMicrofox]

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

[germanjohn]

Defeating a safety feature....not smart.