Ham Radio - Looking at the MX-P50M HF amplifier for QRP radios.

An overview of the amp, and some testing to see how much current it draws.

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[PLS]

Hi Kevin
I bought one of these last year and use it occasionally. The board is exactly the same as your unit with the unmarked MOSFET. My results according to my Daiwa power meter shows the power output, using my FT-818 at 5W constant carrier in, is a maximum of 30 Watts across all bands except 10 Meters that is at about 25 Watts. I have not put it on a spectrum scope so I'm not sure about the distortion mentioned. It does get quite hot when using FT8 or other high duty cycle modes for more than 5 minutes or so. Many thanks for your great videos. 73
VA7DGT

[stridermtk]

Rock that HTX-202! I still love mine, though it doesn't get used a whole lot since I got my FT-4XR

[LibertyEver]

Nice simple design. I like that. I wish someone made a similar amplifier but class E so it's more efficient, using less battery power and generating less heat. QRP Labs has a $26 power amplifier kit that provides 26dB of gain so you'd need an attenuator on the output of a 1-5W QRP radio, as the PA kit is designed to be used as the power amplifier for a transceiver kit. With a 20V power supply the amp can provide a solid 20W out, although it's closer to 10W with a 12V supply. QRP Labs sells low pass filters for $4.60 each, and if you want to select them conveniently they have a $16 relay board that will accept five of the LP filter modules. I might build the dedicated 40W version of that to give my Phaser transceiver kit a 20W output.
If you want 160m operation with the MX-P50M, you could always put it in 80m mode and add a 160m low pass filter in line with the output.

[MattHeere]

I built an amp using this same design (kit from eBay) about a year ago. The higher efficiency comes from it being a straight class B power amp. Most name-brand rigs use a class AB power stage, and so are cleaner, but draw more current. With proper filtering I didn't have any problems with the output on the kit (assuming the transistor bias is set correctly), but I was never happy with the input SWR. I had to run the tuner on my QRP rig - but otherwise it worked fine. The build quality of yours is certainly better than my kit :)

[tristan]

I've got one and it seems to work ok. Opened it to have a look and it has an unmarked part too. It's good that they don't get too hot, which is just as well if the PA module isn't bonded to the case and won't be getting the best out of the heat sink that's available. But Mats Bengtsson makes a point about gain compression, thermal issues could be part of that.

[davidsradioroom]

Nice little video. It's nice to see hams doing things like this.

[warrenmasters]

Thanks, I just had one delivered last week, glad you did this review...

Most of these are made with mosfets pulled from recycled parts...

[PERVISJAYFURLONG]

Good to see you are going well now with new income. You were always a good and genuine guy. I wish you all the best. 73s

[JohnMDiLiberto]

Congrats on confirming your expectation of non-trivial power savings with the new configuration, Kevin.

[davecasler]

You're wearing a sweatshirt in June! Clearly you're no longer in Arizona!

[timsmith]

Good video Kev...I am off grid, and run my laptop on DC. I found online an DC upconverter..13.8 to 20 volts DC. I don't use an inverter for the computer, nor wifi stuff..all 12 volts. The DC upconverter are sold with a cigar plug, for use in a vehicle.

[VKYK]

Kevin, Nice review and look inside the amp. I've had one of these for about 7-8 years now and it was used in my SOTA/WWFF radio pack with FT817, I now upgraded to KX3 but kept the amp and use it with a ELAD FDM DUO driving it with 5w which works with no real difference to when I was using IC7400.
One thing I have found that the plastic power connector was deformed and found it had melted the it together, so have cut out & replaced with powerpole connectors, I would recommend to do this as this could be an issue down the track if you use it on a more permanent basis. Cheers, Adam VK2YK

[chucksayers]

good vid Kevin, bet your glad you got out of Arizona when you did, really hot down there in many different ways. take care

[rzbd]

Thanks. I bought one for the FT-818ND. 73!

[chipandrews]

Awesome video Kevin...Thanks for sharing! I need to get my FT817 fixed (won't power up) and back on the air...with a little amp :)

[don_nskt]

Kevin, very interesting Amp. I want to see how you make it work on the mcHF clone that you have so will be interested in the next video on it. Once you have that, you can use the mcHF for some FreeDV contacts ;)

[eduardopower]

Love this video! Im gonna buy one. Thanks Kevin. 73

[RunningRog]

Hi, great review. I have one of these to use with my X5105 when portable and 5W is not quite enough. It's best used with a resonant antenna then no tuner is required. 73

[raykiii]

Hey Kevin,
I missed where you said you bought this amp. Could you give the information again, please?
73

[frankwco]

Would you know how to take off the black cover that tighten the power wires and signal wire? I’m trying to tap the the wire but it’s really tight.