Saturday, January 1, 2011
Tuna Tin Transmitter Trouble Shooting
That's a mouthful. This is the second electronics kit that Ben and I worked on together as a father/son project. Our first kit was a robotic crab....some kit I found on a website. The circuit board is cut out in the shape of a crab, has two flashing led eyes, and it runs along the floor toward a light source. We were lucky. It worked the minute we powered it up.
The 2 Tinned Tuna kit was our second attempt. We weren't so lucky this time. We did have a lot of fun. One of us would run the soldering iron, the other the solder. Sometimes Ben would tackle a componet all by himself. We fired up the transmitter recently, feeding into a home-brew dipole cut for 40 meters. Ben used our home Yaesu 857d as a receiver. I sent my call sign on 7.030. Well...we get a strong carrier right on 7.030, but instead of a nice CW tone, we get a harsh, buzzing sound. I was bummed, and Ben was ......well....."Dad I told you this thing wasn't going to work". Maybe it was the tuna fish tin and label that took away his faith. For me, it was part of the Maine charm of this kit.
I inspected each of the soldering joints; they all looked fine. I check our compoents to ensure we installed them correctly. Finally, I traced the circuit with a multi-tester and everything seems in order. It's not going to be that easy, I see. I was able to get the original Tuna Transmitter article by the late Doug DeMaw form the QST Archives, www.arrl.org . While have a build that's not working is not 'great', I can see the fun associated with the whole process. The design from my kit has evolved since the original 1976 article, DeMaw does list DC and radio frequency RMS voltages on his schematic. So.....now to build an RF probe and dummy load.....