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Tube Amplifier UL40-S2
Page 2, Sunday November 4, 2001
This is the second part of the UL40s2 tube amp project. On saturday I tried to start with the soldering and construction process, but a soccer match of my son and family visits made it next to impossible to do so. So I had to wait until sunday morning 08.00 hrs -I rose early- in order to come as far as possible with the assembly of the amplifier. As you'll understand, social and family behavior prohibits one from working for 16 hrs straight on this project. But I managed to spend the largest part of my day on this project and I nearly finished it in one day.
In
Dutch we say: With good preparations it takes half the effort. And therefore
I started cleaning my desk, fired up a soldering iron, got myself a small cutter,
a few screwdrivers etc. all within reach. Also I took a small towel from the
kitchen, it will help me to put the amp on when it is nearly finished so that
it will not get scratched or so (part of the assembly is done with the amp upside
down).
And then get started. in the big box I received from Amplimo are a lot of smaller boxes. All tubes are packaged in boxes, and all the resistors and smaller components are shipped in little plastic bags. So the first thing is: unpack everything and start counting. The excellent documentation helps a great deal in recognizing all components.
This is the manual on the left. For me it was in Dutch but I take it that there is at least an English version available and maybe more localized versions as well. And although I think that it is still difficult enough for tube newbies to build such an amp, I agree with Amplimo here: Everybody with a little soldering experience and a little DIY experience will be able to build this amp in 1.5 days. For people without relevant experience it will take a little longer perhaps, but even for these people Amplimo included a small soldering course in the manual.
Let's start with the main PCB (Printed Circuit Board) now. The PCB is dual-sided
but 
almost
all components are soldered on one side only. The other side does only contain
the tube feet, as these have to stick through the 6 holes in the housing. The
PCB is mounted up-side down in the enclosure.
The assembly phase starts with 22 very small soldering lugs with split pen legs that need soldering on the board. This is maybe the hardest part of the hole kit. It's difficult to do, because once the pens are put in a hole through the board, the legs have to be bent apart on the other side and soldered. A little knife helps getting the legs of these soldering lugs apart.
The
second step in the manual is to mount the tube sockets on the board. 
This
is fun to do, for a moment you get the idea how it will look like 12 hrs later,
as the feet need to be aligned properly and this is done by using the holes
in the housing and even mounting the two 6N1P tubes for the preamp section.
---
The tube sockets are the only components that are soldered on the top-side of the PCB, since they will be sticking outside the enclosure with the tubes standing on top of the enclosure later. In order to make sure that the tube sockets will be righly located wrt the holes in the enclosure, they will in first instance not be soldered but loose fitted on the PCB which in turn will be mounted in place.
It is quite easy to solder one (or more) of the sockets a little out of position after which the whole PCB would not (or only with some force) fit in position. Now, we know for sure that everything fits and that all tube connectors stick to the corresponding holes in the chassis without problems, and 
the connectors are soldered in position..
Now we take out the PCB and start soldering the smaller components on the PCB.
We starting with the resistors, and once all are mounted, the PCB begins to look inhabited. Some resistors need to be mounted away from the PCB or even other components (because they will become very hot during operation), but this is decribed in detail in the assembly manual.
Important for a tidy layout of all components on the PCB is to work with a plan. I folded the connecting wires of all resistors around a small piece of wood to make sure that they are mounted all the same. Also, I try to align resistors so that their marking (value) are all readible from left-to right (or top to bottom) with the tolerance ring on the right.
After all resistors are done, we're left with diodes and capacitors, and there aren't that many after all. I did make a mod to the original capacitors in the kit, what/how is described further on this page.
There are things to pay attention to in order to guarantee a long life for
all components 
in
the amp. Some components need to be soldered about 5mm above the printed circuit
board as their temperature could over time damage the PCB (resistors) or just
because we want no high-voltage leaks (diodes). The flat side of my ruler is
just 5mm in height and therefore perfect to control the layout of resistors.
Only the 5 Watt resistors become so hot that the manual cealrly states that
they need to be kept away from other electronics components as their temperature
might damage these other components.
I'm not the type of guy opening up all his 
new
toys looking for ways to "improve" the sound with exotic components
etc. risking warranty void from day one. Even worse, even after living in our
new home for more than two years drilling a hole in my walls feels like drilling
in my own teeth, I just don't like to risk making things worse.
But in this case several people told me that the UL40 may even sound better with a few modifications made. Some could be done immediately and some could wait until later. For example Amplimo told me that the KT88 tubes would even sound better than the standard EL34. (I've read on Menno's site that the KT88 an become unstable under certain conditions so I'm glad not to have done his mod after all).
Fortunately, Triode Dick was prepared to have a look at the situation and give his detailed advice. He advised to start with replacing to sets of capacitors in the UL40 with Black Gate types. Now, I knew Bill Gates and not Black Gates, but the thought to put power on Gates felt good.
On the right you see the two new inhabitants of the PCB (in black od course). The two small 100nF capacitors (C2) have been removed from the PCB. 
To be honest, I did leave the 100nF capacitors in at first, but Dick told me to take them out since in his opinion they were not needed when using Black Gates instead. At that time I did not have any reason not to believe him (and still the BG's do their work brilliantly) so I took my soldering iron and removed the C2 caps from the board.
The last thing that I was able o fix that Sunday was to fix the PCB in the enclosure as well as he two output transformers. I did not make separate pictures of the last two, so all we have here is a picture is Sunday without output transformers fitted.
As you can see, the towel I brought from the kitchen comes in really handy. If you don't watch out with all the metal components and the weight of the enclosure, you will either damage the table or the amp itself (I don't mind the table that much).
The final assembly took place on Monday..
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