6m Mosfet 30w amplifier

Morning All
Having just struggled with a barefoot “817” in EA6 (Airline hand baggage allowance was 5kg so couldn’t take the 857), I need a little extra grunt on 6m. Does anybody know of a working and repeatable design for a Mosfet amp that will give around 30w out for up to 3w in when used with a 12v DC power source please?

tim AT g4ytd.co.uk

In reply to G4YTD:

I don’t have a design, but a kit is available:



Brian G8ADD

In reply to G4YTD:

John GM8OTI is working on one. He’ll link to the info on here when it’s finished.


In reply to MM0FMF:

Hoping to get the 6m one done for October. It will basically be the design in the new VHF/UHF manual using IRF510 devices; probably 2 + 2 rather than the single pair used in the HF amp I built, to get a few more watts out. I tried other devices but wasn’t happy with the (in)stability.

The issue is the 12V; I cart a couple of small (4.5Ah) SLABs up the hill for the HF amp (and the 2m amp too) to provide 24V. The original Packer amplifier http://site.hfprojectsyahoo.com/hf_packer-amp
had a switching PSU developing 24V at 5A (so a decent 12V supply needed!) but I don’t (much) mind the weight of the SLABs :wink:

As Andy says, I’ll let you know how it goes. The HF version gives 35W out for 2.5W in. More on my website, link from qrz.com.


Hi John,

Does it have to be a MOSFET, I have built a couple of these :-


It’s for four, but should scale to six, I found the CB trannies in a “Burner” at a club sale, is should give you the 30 watts nicely.

Nick G0HIK

In reply to G8ADD:
Thanks Brian
Looks like what I need, the challenge now is going to be keeping the weight down for airline travel…


In reply to MM0FMF:
Thanks Andy
(See below)

In reply to GM8OTI:
Thanks for the info John
I have had a look through your web site. The amplifiers look ideal for what I am trying to achieve. 5w and the poor location/aerial were a real bind last week. I would normally take the 857 with me on trips, but we were loaded down with diving gear, clothes and the wife’s shoe collection leaving only one allocation of 5Kg for hand luggage. I managed to pack Lith-ion battery’s, the 817, and wires for 6 to 20m plus travel docs and a thick wad of paper that was the radio license. This balanced the scales at 4.94Kg! (I had to carry my wallet and mobile in my pocket to make the weight…).
I will keep checking the web site and look forward to seeing the finished unit.
Thanks again for the info.

In reply to G0HIK:
Hi Nick
No, Mosfet or device type is not important although I have a handfull of 510’s here looking for a design. The 4m amp looks interesting, but as I dont have the device a quick look on ebay shows they are available for around $80 U.S making it pretty expensive to build. I have printed a copy of the circuit off and made a note that if I ever see a transistior floating about I will liberate it and chuck it in the amp!
thanks again for the reply.