Q. What crystal does the 555 use?
A. The 555 uses a dual conversion crystal. The part number is 66772xx (xx= channel number). To tell if your crystal is dual conversion or not, examine the pull tab. If the tab has a blue end and the letters 'RF' on it, then it is a genuine Hitec dual conversion crystal. Use only genuine Hitec crystals in the 555 or it will have decreased range.