I want to find the history behind my Tri-State Electronics of Falls Church, VA, Tri-State 500 Transmitter. I have a copy of a manual that is supposed to be for my transmitter, but there are some differences and the vintage of the unit is not mentioned. This transmitter uses a single 4X150 in the final and includes a Collins Mechanical Filter after the balanced mixer. The transmitter covers the 80, 40, 20, 15 and 10 meter bands, has an input plate power rating of 500W PEP-SSB, 400W CW, and 300W AM. The unit is made for rack mounting but came in a heavy steel cabinet. All comments are appreciated. Thanks.