Tube Tracer Build 2 - Added features

Auxiliary Heater Supply

Since the heater supply of uTracer has its limitations at low heater voltages, I decided to include an auxiliary supply for the few cases where low heater voltages are needed. This created a need for a switch between the internal and auxiliary supplies. The Chinese buck converter takes its input from the same laptop supply and has a small footprint on the face panel. 

The auxiliary heater supply has both voltage and current regulation.
The output voltage has in theory no lower limit.

One can justly argue that the design could be smarter, but I just did not want to have any complicated sidetracks in this project. The only actual drawback is that since the auxiliary supply uses the same 19 Volt supply, it shares a common ground with the uTracer and cannot be used with directly heated cathodes.

Case Modifications

The design required that the face plate needed something to get fixed to. Therefore, I attached aluminum L profile with rivets inside the original aluminum frame of the case. I needed to remove some of the foam rubber padding so that the aluminum frame was free of any padding.

I used 10*20 mm profile on three sides and 25*25 profile on the frame back, where the hinges create more stress. The two upper rivets of the original hinge hardware were removed and replaced with screws that were drilled also through the L profile.

The AC input was connected to the case in the right back corner. The case body is made of Masonite with ribbed red outer surface. Making the necessary holes for the IEC male connector in the wall was easy but the screws need to be secured with decent size washers and nuts

In the final steps it became evident that some of the foam padding on the lid frame was interfering with the closing of the case. It was necessary to remove 2-3 mm of rubber foam from the edges of the lid. I could have made a cleaner finish if I just took my time to fetch better set of tools for the task.

The Face Plate

I designed the uTracer face to be mostly empty. Only the auxiliary heater supply, fan intake and the indicator LEDs break the surface. The tube adapters cannot be completely hidden but I hoped that they would not be much visible under normal operation. The tube under test has a prominent central position.

My visual image was very neutral – white or grey. After many iterations I ended up using aluminum composite material called Dilite, which has two 200-micron sheets of aluminum and 1.6 mm of black polyethylene between them. There are many different surface colors available but mine has warm satin white finish on both sides.

I hoped to have access to a CNC router, which could cut the desired shape cleanly and accurately. Unfortunately, the size of the face plate, 390 x 240 mm was too big for any CNC machine in my neighborhood, so I had to cut the rough size using a table saw and the openings with a scroll saw. Dilite was very easy to work with. Cutting with a carpet knife and finishing with files and sanding pad resulted in totally clean edges.