[old_tv_nut]

If the oscillator uses the crystal alone as a series resonant element, the crystal is tuned to be series resonant (a short circuit) at 3579545 Hz. However, nearly all chroma oscillators use a crystal in a "parallel resonant" mode. I put "parallel resonant" in quotes because the crystal is not tuned to be parallel resonant in itself, but to be inductive, so it can be either series resonant or parallel resonant when combined with a small amount of capacitance (consisting of both strays and discrete separate parts). In this mode, the crystal acts as a very large inductor resonating with a small capacitance, and the combination is resonant at 3579545 Hz. The crystal series resonance in itself is then a few hundred Hz different from the correct frequency. Common values for the total tuning capacitance would be in the range of 20-30 picofarads. The value of capacitance for which the crystal is tuned is specified in a manufacturer's part drawing, but not in service literature. Generally, crystals made for different values of capacitance can be substituted because in most cases the oscillator center frequency can still be tuned to the correct value; however, the pull-in range and hence the temperature drift will be different than intended.