I have two transmitters, a Hallicrafters HT-17 and a Harvey Wells TBS-50c that I intended to use these two crystals for. The 3513 Crystal works in both radios, the 3531 crystal only works in the HT-17. I cleaned the 3531 crystal several times, but to no avail. The lack of excitation on the 3531 crystal is NOT the fault of the seller, these crystals are over 80-years old and have deteriorated.