A helpful device for maintaining constant tension in the contact wire during overhead construction.
Parker Williams (1927-2010) was my trolley modeling mentor when I was a young pup in the 1980's. I met him when he was in the process of installing the overhead for the trolley line at the San Diego Model Railroad Museum at Balboa Park. He was using a device similar to the one pictured above and I instantly saw the merit of such an apparatus, so I built my own based on his design.
The idea is to maintain a constant tension of 12oz on the contact wire while its being soldered to hangers, crossings and pulloffs. Its biggest asset is that it frees up my hands for the soldering iron and the span or pulloff wires or hardware.
Its construction is pretty simple. A heavy base (Parker knew a guy who used a heavy ashtray!), I used a block of Iron (incorrectly labeled here as "steel"), with a rubber pad on the bottom to prevent slipping. Drilled about 3/4 of the way through to accept a 1/2" brass rod. Patio slider wheels have a nice concave contour that are perfect for channeling the fishing line that the 12oz weight hangs from. The clamp is a little tougher. I used half round brass drilled to accept a thumb screw. The bottom half is threaded for the thumb screw to tighten into. But it would have probably been easier to just tie a mini clamp to the line.
A Tension Tower isn't required for constructing overhead. The SCTC does just fine without one. But it sure helps to have that extra hand. Yes sir! It sure helps!