GH Engineering 72W 23cm Amplifier (a la G6LVB)

(Updated 27 December 2000)

The amplifier was supplied from GH Engineering and I picked it up at the last Picketts Lock London Rally in Winter 2000. Cost about GBP300 excluding heatsink.

That meter's on the 200W setting. measures 72W on the dot. With only 0.5W in.

There's something about the GH Engineering kits - every one I've built (all three) has worked first time.

I should also note that you should check and double check that all the contents are included prior to starting out. All three of the kits I've built have had bits missing. The worst offender was a missing MOSFET in the 72W monster. I sourced this myself from RS (not Radio Shack for our Stateside readers - RS in the UK is more like Digikey or Jameco) as I was in a hurry. Other minor components missing have included a diode and a couple of resistors, which I had in the shack anyway.

I am by no means an expert in SMD or microwave technology. The only other 23cms stuff I've built are two other amps from GH Engineering. These kits are the first time I've done SMD work other than removing diodes from European radios to allow them to be used in the US. Invest in a nice small tipped soldering bit and some tiny small nosed pliers.

Other things to note is that drilling and tapping the heatsink takes a good deal of patience. What I found really useful here was a GBP39.95 vertical bench drill press from B&Q. Interestingly by coincidence I see that GH Engineering is recommending these now. That drill saved saved a lot of time - and probably more than a few mess ups too. At GBP39.95, there's really no excuse. Don't even think about drilling that heatsink freehand. A very, very good selection of drills is also essential: 1.8mm, 2mm, 2.5mm, 3mm, 3.2mm, 3.5mm; list goes on. And you _do_ need them!

Now until the GH Engineering kits I've never tapped a hole in my life. Why they never taught me this at school at metalwork I'll never know. However I always remember that the teacher was a jerk. There. I've finally got that off my chest after over 20 years. Well, I now know how to tap a hole. And so will you... there's several dozen to do! You can buy the heatsinks pre-drilled if you like. But hey, I like living life dangerously.

Building the electronics is straightforward. Patience, a steady hand and a clear flat surface are a virtue - accidentally losing those SMD's in the carpet of the shack is a nightmare.

The finished beast

It took eight hours to complete. Four hours were spent drilling the heatsink and other metalwork, and four hours on the electronics and wiring up.

This 72W kit was also the first time I've used semi-rigid cable. I found that you need a lot of patience with this. I used a sharp craft knife to strip a 2 or 3mm off the ends. I recommend having a few practice goes first. Unfortunately there's not much included with the kit to practice with.

I recommend, if you've never done this sort of plumbing work before, that you try the less demanding 18W version first. A lot less drilling. Took me an evening to build the 18W version.

As a final note, get your overall case and heatsink arrangements sorted out before you start drilling. I used an old busted TE Systems 2m Amplifier case and heatsink which was about 2" too sort in length as you can see. Hey, I'm not proud. Keep those fingers clear though. You could cook a turkey with this baby.

Mail Howard, G6LVB