I have seen them on several Singers, and I assume many have had them. My 99K from 1934 had two cylinder shaped condensers (supressors?) just above the plug under the hand wheel. They were just a bit larger than AA batteries, with a wire out each end. I have seen this type on most pre 1950s machines. Later models tend to have small plastic square near the motor or in the pedal. I am totally envious to the person who ends up with this machine.