1-2. The WRL Model SM-90 Screen modulator is made by WRL Electronics, Inc. of Council Bluffs, Iowa. The Screen Modulator is designed specifically for use with the Globe Chief Transmitter, Model 90; but may also be used with any other transmitter such as the Heath AT-1, Johnson Adventurer, Knight 50 Watt Transmitter, etc. using one or two 807 or 616 tubes in the final R.F. amplifier, with suitable modifications. The Screen Modulator permits radio-telephone operation of a C.W. transmitter at minimum cost. 1-3. DESCRIPTION. 1-4. The Model SM-90 Screen Modulator is completely self-contained in a chassis, with the tubes and interstage transformer projecting above the chassis. An octal plug projects from the chassis and plugs into the auxiliary socket on the rear of the Model 90 Globe Chief transmitter, providing all interconnections between the two units and mounting the Screen Modulator on the Globe Chief.