I have never aligned a mux part of a receiver, so I can't be much help, but, here's what I know. The 19 kHz. would be a sine wave. The station sends it out at 10% modulation on the main carrier. The main channel has both the right and left channels mixed in phase (L+R), and put out as a monophonic FM signal, just like always. The phase of the right channel is then inverted, (L-R) and double sideband modulated on a 38 kHz. sub carrier.

Since there is no carrier in DSB modulation, The station also inserts a pilot of 19 kHz, at 10% modulation. The station can also put elevator music on a AM sub carrier at 64 kH. The 19 kHz. is detected, and turns on the decoding circuits (and the stereo indicator light).

The 19kHz. is doubled to 38 kHz., and this is inserted into the subcarrier demodulator as the carrier. The decoding circuits demodulate the subcarrier to retrieve the (L-R) signal and add (mix)and subtract (invert the phase and mix) that signal from the main channel (L+R). So, (L+R)+(L-R)=2L, and (L+R)-(L-R)=2R, and you have your stereo back. (L-R) equals the stuff that is not stereo, while (L+R) is the monophonic component of the stereo, so you get both channels on a mono receiver.

The tricky part is that the 38 kHz has to be almost exactly in phase with the 38 kHz. that the station inserted in the transmitter)of coure,inserting a carrier at 90 drgrees out of phase would result in no demodulation, so you could actually put two subcarriers 90 degrees out of phase, and have three signals on one main carrier, but I don't wabt to talk about color TV on a radio forum. You would have to have 40% modulation an the main and sub channels, 10% on the pilot and the last 10% for your background music, which is on a 64 kHz. subcarrier, which requires an AM detector.

As to the scope, what you see on the scope will depend on where the sccope is connected. Maximum and minimum deflection means biggest and smallest peak-to-peak sine wave Voltage.

I hope this helps.
Lewis