Bandspread vs range continued from previous post

If you observed the effects of adjusting the Vcap ratio by adjusting the low end capacitance and the high end by adjusting the "trimmer" It should be easy to understand the importance of making the adjustments in order. The 600KC adjustment sets the bandwith while centering the range over the correct dial point. The 1400KC adjustment sets the high scale to the correct point. You must work between the two to get the proper operation of the set. Both effect both ends of the scale so the 1400KC could be adjusted without first setting the 600KC and then you are looping back and forth with to wide a band. You can set the dial to 1400KC and adjust either one adding the low range adjustment while reducing the high range adjustment and hold the output steady. Anywho here are a couple of excert from the service manual.

The alignment procedure on one sheet.

Setting the bandset for a LC tuning circuit.

As simple as I can state it the tuning range is determined by the CIRCUIT high to low capacitance. When you look at a schematic you may se the Vcap range is 0pfd to 360pfd but that is just the Vcap you will also find trimmers and strays in the circuit. The sim's work through a series showing the hi-lo tuning with a Vcap and strays. Once the circuit is set and the range determined I adjust the strays to show the effect. Then I use the same circuit and adjust the inductor. You should be able to see the ratio of hi-lo capacitance sets the tuning range while adjusting the inductor shifts the band being covered. One way of looking at it is the band being covered is definrd by a VEE. By adjusting the capacitance you widen or reduce the VEE's width. Adjusting the inductor will slide the VEE across the band to establish the center point. We can hit a brick wall when aligning a set by making the wrong adjustment first. Consider this: the range is defined by the (VcapHI plus strays) / (VcapLO plus strays). Look at the schematic, do you see capacitors in the tuning circuit? You must add them to the Vcap values to establish the range. Next time you find an impossible to align set consider this: set the dial to the low point and find the frequency being received. set the dial to the high point and find what frequency is being received. Divide the measured high by the measured low and square it to determine the actual tuning range. Divide the dial high by the dial low and square it to determine the desired tuning range. If they are not close it is time to examine the extra components in the circuit. So the goal is to set the width of the VEEs arms and the center point of the range. Hummm? Makes me wonder about that "set the dial to 1400kc and adjust...". Oh well now for some screen shots.