After the successful build and test of my bench model of the Gibson GA-5 I decided to build a complete version of this amplifier in a case. The Gibson GA-5 came out as the Gibson Les Paul Junior GA-5 in 1956. The GA-5 is very similar to the Fender Champ which originally came out in 1948 as the Fender Champion 800. In 1955 Fender renamed the amp as the Champ and I’m tempted to think that Gibson just made a copy at that point. There is a bit more history in this article.
I had recently acquired a Fender Champ (like) wooden cabinet which was very nicely made from some sort of hardwood (those were the days). The amp cabinet came in the original Fender cardboard box complete with original packing materials. I do not have any idea when this case was made. It just looked nice and seemed like a home for my GA-5 replica.
My daughter had been put to work assembling the bench test model but wasn’t interested in building the real amp, so I did the woodwork, metalwork, electronics, finish work, fabric work, you get the idea.
As with many of my projects there is a certain amount of inventiveness especially when it comes to fabrication. I try to make use of materials I have on hand as you will see in some of the pictures. But for the electronics I bought all new parts and the result is very pleasing indeed. For what is essentially a 5 Watt amplifier, this is perfect for playing at home (in your Les Paul or Eric Clapton mode), but also perfect for a studio session to get back to that 50’s sound.
I took the finished amp over to Russ Kruse who is a life long musician and runs Florida Tube Amp. Russ liked the amp which he declared as “Way better than the GA-5”. Good enough for me. Here is a short clip of Russ playing guitar through the amp in his shop. If the video won’t play here, it’s also on my YouTube channel here.
So why is it called a “Gubbins-5”? Well, that’s thanks to my daughter who commented when she was building the bench test version that it “has a lot of gubbins in it”.
The amp is very close to the original Gibson schematic but has a solid state rectifier, not a tube and modern transformers and speaker. I’m inclined to think that the Hammond transformers and Jensen speaker are the biggest improvements over the original amp.
So let’s take a look at what was involved in building this little gem. The first phase was to made a speaker board to fit in the case. I wanted to be sure that once the speaker was in place my amp chassis would fit OK. I actually modeled this in Fusion 360 so I could move parts around to see how it looked. At this point I was thinking that perhaps I’d get a metal chassis made for me from my design.
The speaker fabric came from Speaker Builder Supply and although it’s not at all like the usual GA-5 fabric I thought it gave it a nice dark look. The fabric is actually a copy of a Fender design. More than once I thought I was really building a Champ replica but I’m sticking to it as a GA-5 copy.
The chassis was made from two pieces of aluminum angle and a piece of super-secret lightweight material I found on Home Depot’s web site one day when I was looking for aluminum sheet.
I based the construction on the same tag strips I’d used for the bench model. I had to work a bit to squeeze both the transformers in at one end but that had the advantage of giving more space to wire up the electronics and keeping both transformers away from the input end.
Building things like this on the fly is very dependent of having all of the parts available so that spacings, hole sizes, and so on can be determined. Despite this, it’s almost always the case that I find something I don’t like when I do the assembly. In this case I had drilled all the holes and assembled the metalwork only to find I’d forgotten the fuse holder. There were a few other minor issues along the way but it went together quite well for a first time build of this design.
The electronics assembly followed the same approach as used on my bench model. All the components were fitted to the tag boards and then wires were added to the tube sockets and so on.
The next step was to put the electronics chassis into the cabinet and make sure it all fit before finishing the woodwork.
After the assembly was completed it went on the bench for a sound check and then over to Russ Kruse’s shop for a quick evaluation. I replaced the volume knob with a more traditional chicken head model and declared the amp finished.
