The 6L6GAY is the military version of the EL37 6L6-type electron tube. It features "coke bottle shape black glass" and is considered of superior quality. The EL37 type is considered about the best of the G, GA, GB, or metal 6L6 types. Matched pairs of these tubes are considered rare in the United States, and thus command a high price for the tube enthusiast.
The United States Army officially describes the 6L6GAY as "ELECTRON TUBE, BEAM POWER AMPLIFIER, RECEIVING TYPE 6L6GAY."