Plug In Coil
The Gambrell coil was different to other makes at the time because the coils were wound in separate, spaced layers and not on top of each other as in a honeycomb coil. The ribbed pattern that you can see in the photo are from the ebonite strips that hold the layers in place. Gambrell patented this method of construction and a review of it was printed in Wireless World (dated September 1923). The advert shown below is taken from Modern Wireless magazine dated December 1923.