Chinese Amp Kits

[G6JIE]

Has anyone had a similar experience with these Chinese kits.
I ordered a UHF amp and when it arrived I thought great 28 quid what could go wrong.
Well, just about everything, it was the wrong kit, it was a VHF board, half the bits were missing, none of the SMD parts were identifiable, the MRF186 was attached to a bit of secondhand pcb, they did put it an anti static bag bless em, no circuit and no instructions.
After about 20 emails backwards and forwards no chance of making them understand they had supplied the wrong bits, so I gave up.
Be aware if you buy these kits be prepared for a bit of work.
Some pics for reference.

PS
Postman Pat's missing head is nothing to do with me

[G4GUO]

Hi,

I bought one of those kits (VHF version). I have not had time to put it together but a BATC member emailed
(Dave G0MXW) me the instructions on how to build it. If I ever get around to building it I will let you know how I got on.

The transistor supplied MRF186 is not really suitable for VHF operation so I expect it to be either be very lively
of not work at all. I was planning on substituting a different device in it.

- Charles

[G6JIE]

Hi Charles
Could you post a pic of the pcb.
thanks
Dave

[G4GUO]

DSCF7458.JPG (851.85 KiB) Viewed 12544 times

[G4GUO]

Since my original post I have noticed that K5TRA has used that device to make
144 / 220 / 430 MHz amps so maybe there is hope
http://k5tra.net/TechFiles/VHF-UHF%20Re ... 20LNAs.pdf

- Charles

[G6JIE]

Thanks Charles
Same board as mine.
Let me know if you have enough parts in the kit to build it.
thanks for the link.
73 Dave

[g0nzo]

Ok, this thread has been quiet for a while. But possibly someone has something more to add?

After seeing these and reading the info at:
http://g4fev.atspace.com/mrf18670cm.htm
(and the 2mtr kit write upon that sit too.)
I brought some of these kits for 2 and 70.

The 2mtr kits worked pretty much first time. An easy 100watts and even got towards 150watts with 28V and darving hard. But that is getting silly given the ratings of the device.
So I am going to combine 4 of these to get 400watts. (And poss 40watts on DATV.)

I'm trying out the 70cm version and not having as much success.
I am seeing a poor input match, even using the longer phasing line lengths, in the above link. And only about 45watts out. With a bit more drive, because of the poor match.

Anyone had any joy with these?

[g0mjw]

Thanks for the interesting link. My question would be is it worth it given the cost and availability of devices like the BLF184 that can be used to build a stable 400W amplifier with just one device without all of that messing about combining multiple lower power modules. The devices is just over £100 which I admit is a lot but by the time you have put together all the bits for 4 x MRF186s its not unreasonable.

But, assuming there is a need for 250W modules I am wondering if anyone has tried using pairs of 900MHz transistors on 70cm. The MRFE6S9160 which was available for 10 Euro that DF9IC was using to produce over 150W on 23cm for example. http://www.df9ic.de/doc/2015/mmrt_2015/ ... Hz_PAs.pdf

Mike

[g0nzo]

Mike,

I agree, not the simplest route. But I brought a couple to tat with, and the idea grew from there. And I was already half way.

Probably similar to the story of the yocal sat on the village wall, when a townie pulls up to ask for directions. The reply being "well if I were trying to get where you're goin', I wouldn't start from 'ere !"

Jules

[g7ntg]

I have used lots of these amps and for the price they are very good. The VHF ones are great for 4m with higher value coupling capacitors. The UHF ones need tweaking abit to get the power output up.