I think that previous to sp600 receiver, Hammarlund maked the sp400. The sp400 is very similar to the later sp200's. Here is the only reference I can found about it: http://www.dxing.com/rx/sp400x.htm , where the production years are indicated as 1946-1948. I have one sp-400-sx rack-mount unit, which slightly differs from the sp-200/bc-779, and was probably made in 1947. --LU2DFM190.188.110.156 (talk) 11:57, 9 February 2008 (UTC)