Ultrasonic chromaticity delay line application circuit

The following figure shows an ultrasonic chroma delay line circuit. DL in the circuit is an ultrasonic chroma delay line. VT1 is a chroma signal F delay amplifier, VT2 is a red difference signal component V signal amplifier, and VT3 is a blue difference signal component U signal amplifier.

　　The signal output from the collector of VT1 is divided into two paths: one path is added to the 4.43MHz parallel resonant circuit composed of Cl, Ll and DL input capacitors, the signal enters the delay line, and its output signal is added to the primary of Tl, and the positive and negative delayed signals are output from the upper and lower ends of the secondary respectively.

　　The other path is added to the parallel resonant circuit of C2 and L2, and then added to the secondary center tap of Tl through C3, the moving plate of RP1 and C4. This signal is added to both ends of the secondary coil, and is added to the positive delay signal to obtain the ±V component signals and sent to the base of VT2, and subtracted from the negative delay signal to obtain the U signal and sent to the base of VT3 to complete the delay demodulation.

　　The parallel resonant circuit of C2 and L2 is used to make appropriate delay adjustment for the direct signal to compensate for the delay error of DL, because the direct signal and the delayed signal should differ by exactly 1 line plus 180 degrees in order to remove the signal of the other component in the addition and subtraction circuits.

　　Adjust L2 to change the resonant frequency so that the direct signal and the delayed signal are exactly delayed by 1 line plus 180 degrees.

　　By adjusting the moving piece of RP1, the size of the direct signal can be changed, making the amplitude of the direct signal equal to that of the delayed signal, so that the signal of the other component can be removed when adding or subtracting them.