amplifier_projects

YU1AW GI7B 144 MHz Amp

Last update 21 May 2014

Well I have started with my 2 x GI7B valve amplifier who's design is based on the well known YU1AW design and also construction details of the amplifier here. I will explain how I built my version and any challenges I have come across, in the hope that any of my "learnings" can assist others to build this amplifier.

The reason I have chosen this design is that the information available is easy to follow and looks easy enouth to duplicate. I have used no special tools, except the drilling out of the slots of the Plate Line adjusting Z piece (Lt) so as to align the slot for adjusting the resonance, a "Compound Vice" was used which made life a lot easier.
Additional to this I made a "Press Brake" to bend the copper "Plate Line" and also to bend other pieces as required. I have long wanted such a tool in my garage, so now is as good a time to make one for myself.
It is quite hard to bend 1.2mm copper plate accuratly without this device and bending it in a standard vice ususlly ends up in a mess. The cheap "Press Breaks" tend to only bend up to 1 mm thick and are narrow. By making one up myself, I am now able to bend a little thicker that 1 mm copper and aliminium (2mm Ali) and sides for the project outer. I will document this on another page on how I built the "Press Break".

Here you can find construction photos, in no particular order.

(Still in progress)

Here is the diagram

Construction:
For the Plate capacitor, I had the engineering yard cut the copper sheet for me to the correct size as a "hack-saw job", would not have come out so nice and not worth the hassel. I also used a tool similar to the "Dremel tool", to cut out further as necessary. I first marked out all the measurements and bending lines then for accuracy, I pre-drilled some of the bigger holes then the rest to the correct diameter. Once I finished bending I sanded all the copper with 600 waterpaper to get rid of any sharp points that might penertrate the PTFE

1) Pre drilled 1.2mm copper sheet

2) Plate Capacitor cut out and marked ready for drilling and bending.

3) Drilling the plate adjustment mount, (Lt)

4) The 3 holes in the middle are only for steading the plate while drilling out the slots to keep alignment

5) Completed, ready for bending. I used a Dremel tool to cut the slot edges strait and then sanded the edges.

6) Bottom piece of the Plate Capacitor, drilled and ready.

Top

7) Vice bender to bend reverse bends that cannot be done in the home made Press Break.

8) Lt finished. I had to do a bit of un-orthodox hammer hitting to get the plate to the right height as I was not familiar with the benders and the amount of adjustment one has to give for the bending radius.

9) La and Lt conected up with 6 M3 screws, I just need to clean up the slots a bit so the slots slide easily with La.

10) Bending C0, I used my home made tool and also the Bench Vice bender.

11) GI7b's fitted. I originaly did the bend angles too large and then had to flatten the bends to achieve the correct height of 28mm as per the diagram.

12) Another view. Note, holes will have to be drilled through the copper to improove airflow through heat sinks