Abstract: Projection TV systems comprise plactic lens and CRT assemblies arranged to project an image onto a screen for viewing. The focus of the lens varies with ambient temperature around the lens as the temperature increases from turn-on of the projection TV system to a warmed-up condition of the system. There is disclosed a temperature compensating mechanism for the lens. The mechanism may be incorporated into the lens to cause direct axial movement of a lens element or it may be attached to an external focussing adjustment of the lens. Several embodiments of the mechanism are disclosed employing either a bimetal or a piston slidable in a cylinder with the cylinder being filled with a material that expands with temperature. The piston and cylinder assembly is used in the preferred embodiment with the cylinder housing attached to the lens housing and the piston directly connected to the external focussing adjustment of the lens.

Abstract: A system for the automatic correction of convergence and gray scale in color television employs light sensors, either singly or in an array, on the beam landing face of a cathode ray tube or on the screen of a projection receiver. The sensors can be placed in the overscanned area of the raster, such that they are outside the normal viewing area, or in the viewing area if the sensors are made sufficiently small. In the vicinity of a sensor, two of the three cathode ray tubes or electron guns are blanked. As the light beam, in the case of a projection system, crosses the sensor, an output is produced. This output is processed to obtain accurate timing characteristics. Since the position of the sensor is known in terms of counts in both the vertical and horizontal directions, error signals can be developed by comparing the timing of the sensor output with the proper count.

Abstract: A VIR signal detector circuit for a color television receiver identifies the repetitive reception of a VIR color information signal on a predetermined horizontal line of video signal. The detection is accomplished with minimum interference from Gaussian and pulse-type noise to assure that VIR color control circuits in the receiver are activated only upon receipt of an actual VIR signal. The VIR signal detector operates by generating a viewing pulse of short duration during each horizontal line in which a VIR signal may be present. An accumulator, set to respond to a predetermined number of simultaneous detections of the viewing pulse and a video signal exceeding a predetermined value, generates a control signal indicating that a VIR signal is being received.

Abstract: A field effect transistor may be used as the mixer in a VHF varactor tuner by the use of self-adjusting bias. Both maximum conversion gain can be realized when the oscillator injection voltage is low and low intermodulation and cross modulation products realized at higher oscillator injection voltages. Bias modification is achieved by use of the tuning voltage in a bias control circuit where FET drain current is adjusted while FET bias voltage is maintained substantially constant. Keeping the bias voltage for the FET substantially constant insures constancy of the FET input and output capacitance which in turn preserves the tuner's tuned circuits from being detuned and variably loaded.