For a while I used my Tuna Tin as a quick and dirty way to test crystals--not the best approach but it worked. In playing around with simple tube transmitters, I found myself needing to grind down some FT-243 crystals. I decided to build a dedicated crystal tester to make this easier.

The design is a simple Colpitts Oscillator built Manhattan style and mounted in an Altoids tin. The crystal is connected through test leads and the output through an phono jack.

Other than grinding FT-243s, my most common application is to quickly test a crystal or to match crystals when I'm building a crystal filter. For these types of tests I typically feed it to my frequency counter.

This is one of those simple, but useful projects. It was my first real success with Manhattan style construction. Also, in the interest of keeping better documentation on my projects it was my first serious attempt at pulling together a schematic diagram on the computer.