Chinese MiniPA-100 Kits

[Rick Miller]

I just wanted to share my recent build using a cheap $35 kit off of eBay.

I also bought a 100W BPF to go with it for an additional $50 or so, and a 2-pill case from ICA manufacturing and I now have what seems to be a decent little amp. I'm getting 100W+ on all bands using my FT-817 to drive it.

I don't have a spectrum analyzer yet to see how clean it is, but on air reports have been great. My fist contact was a guy in Brazil and he gave me a 5/9 from North Idaho. Input SWR seems perfect, I've read other saying they've had high input swr, but that isn't the case for me.

What's really interesting is the device, it uses a MRF9120. Looking at the data sheet it appears this device was meant for 880MHz @26v 120W. I'm easily getting 100W @14v on HF.

Anyone else played around with these kits?

 

[freecell]

nice job Rick. functional, simple and straight forward.

https://www.nxp.com/docs/en/data-sheet/MRF9120.pdf

 

[Rick Miller]

Just adding another pic, of the inside...

 

[Shockwave]

I just wanted to share my recent build using a cheap $35 kit off of eBay.

I also bought a 100W BPF to go with it for an additional $50 or so, and a 2-pill case from ICA manufacturing and I now have what seems to be a decent little amp. I'm getting 100W+ on all bands using my FT-817 to drive it.

I don't have a spectrum analyzer yet to see how clean it is, but on air reports have been great. My fist contact was a guy in Brazil and he gave me a 5/9 from North Idaho. Input SWR seems perfect, I've read other saying they've had high input swr, but that isn't the case for me.

What's really interesting is the device, it uses a MRF9120. Looking at the data sheet it appears this device was meant for 880MHz @26v 120W. I'm easily getting 100W @14v on HF.

Anyone else played around with these kits?

Using a 26 volt part on a 12 volt system, will reduce the gain and overall output considerably. However, using a UHF part at HF frequencies has the exact opposite effect, with a dramatic increase in gain. The end result is the part is making very close to its rated output power even on 12 volts.

This is considered acceptable practice and most likely produces an amplifier that is more rugged than usual. It provides a lot more headroom in the area of breakdown voltage which is a common failure point for transistors. Fuse it with a fast acting fuse just under the maximum drain current and it should be fairly bulletproof.

 

[Rick Miller]

Using a 26 volt part on a 12 volt system, will reduce the gain and overall output considerably. However, using a UHF part at HF frequencies has the exact opposite effect, with a dramatic increase in gain. The end result is the part is making very close to its rated output power even on 12 volts.

This is considered acceptable practice and most likely produces an amplifier that is more rugged than usual. It provides a lot more headroom in the area of breakdown voltage which is a common failure point for transistors. Fuse it with a fast acting fuse just under the maximum drain current and it should be fairly bulletproof.

I wasn't sure it would do a full 100W when I first started building it, and when I printed the front label I decided to call it a 75 which oddly enough does align with an AM dead carrier. The XU portion comes from my callsign KK7XU.

Next up I've got everything I need to put together another amp, I plan to use 4 2879 C's. My original thought was to use a MRF101 50V device as a driver, just as a learning tool. But now I think I'll just use another one of these kits instead to keep it all at 14V. I wasn't a fan of dual power supplies anyhow. It will be a base amp with an old iron core UPS transformer for the PS.

 

[443]

Neat. This comes WITH the MRF9120 (from China) for like $48? (no heatsink)

 

[443]

Using a 26 volt part on a 12 volt system, will reduce the gain and overall output considerably. However, using a UHF part at HF frequencies has the exact opposite effect, with a dramatic increase in gain. The end result is the part is making very close to its rated output power even on 12 volts.

This is considered acceptable practice and most likely produces an amplifier that is more rugged than usual. It provides a lot more headroom in the area of breakdown voltage which is a common failure point for transistors. Fuse it with a fast acting fuse just under the maximum drain current and it should be fairly bulletproof.

Just curious what you think. I seem to remember, years ago, reading about how if you do this sort of thing, specifically running a DC power transistor like the MRF9120 and many others intended for 28V or 48V etc systems, at 12-14VDC instead, you end up with the transistor producing a lot of IMD, more than it would if run at it's intended voltage. Just curious of thoughts, I have never tried it. Have used UHF parts for HF before though.

 

[443]

I would like to play with one of these kits. If it's not against forum rules here, any recommended sellers? And approximate time to delivery? I see on eB ay at least they are only available from China shipping.

 

[443]

I just wanted to share my recent build using a cheap $35 kit off of eBay.

I also bought a 100W BPF to go with it for an additional $50 or so, and a 2-pill case from ICA manufacturing and I now have what seems to be a decent little amp. I'm getting 100W+ on all bands using my FT-817 to drive it.

Rick, what drive power are you using? The full 5W or did you reduce it any?

 

[Shockwave]

Just curious what you think. I seem to remember, years ago, reading about how if you do this sort of thing, specifically running a DC power transistor like the MRF9120 and many others intended for 28V or 48V etc systems, at 12-14VDC instead, you end up with the transistor producing a lot of IMD, more than it would if run at it's intended voltage. Just curious of thoughts, I have never tried it. Have used UHF parts for HF before though.

I would have to say your statement is 100% correct. Anytime you operate an RF output device at reduced voltage, they're pretty much has to be an increase in the IMD levels. For example I would not expect this particular amplifier to run as clean as a pair of 2SC2879s in class AB, operating at 60 watts PEP per device. On the other hand, I would expect this amplifier to exceed the IMD characteristics of any amplifier using switch mode power supply transistors. They don't even publish an IMD rating for linear RF applications because they were never designed for that use.

 

[Rick Miller]

I would like to play with one of these kits. If it's not against forum rules here, any recommended sellers? And approximate time to delivery? I see on eB ay at least they are only available from China shipping.

I got mine from eBay/China, took about 3wks to get them. I bought three of them total, and have now built two. Both seems to be working great, I did not modify or have to do any tuning at all. The only thing I changed was the wire on the transformers, opting for ptfe wire instead of whatever the hell came with the kit. And I do run them with a bandpass filter.

 

[Rick Miller]

Rick, what drive power are you using? The full 5W or did you reduce it any?

I didn't add any attenuation, I was concerned that I may need to, but after testing it seems to run like a champ. I blasted away on FT8 for 2hrs straight until my radio was way too hot. The amp however was only slightly warm to the touch. So based on how it's working I think it's fine with 5W. Made 39 QSO's in that 2hrs in 9 countries just testing it out.

 

[Rick Miller]

My next project will use a pair of MRF300AN/BN transistors running 50V. I started assembly this weekend but am waiting on components for the bandpass filter which will take over a month to get here. In the meantime I will get the pallet assembled and tested.

I'm quite interested in this device, anyone here have experience with the MRF300's?

I changed my mind on the 2879C's after reading the specs and seeing a few videos online. I'll just save those transistors for a future repair or some such.

 

[443]

My next project will use a pair of MRF300AN/BN transistors running 50V.

Very interesting. Where have I been? A LDMOS in a TO-247 package. Now that's something else. Only issue I could see, after having spent 14 years replacing blown high power TO-247 (400-500V) Mosfets in audio amplifiers (for cars, KW+ size amps) is that you would want to make use of copper heatsinks (if you can), copper heat spreaders, whatever you can to help with this parts heat from that type of package (relatively small). It should be fairly efficient, however 320W per device (rated power), I would ensure it can spread that heat out quick if needed.

Looks like Input Capacitance is not too crazy high, should be real easy to drive.

 

[443]

BTW: I love how the MRF300AN Datasheet from NXP give a 27Mhz Reference Circuit Layout and parts list. LMAO. It's like they know what's up.