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Old 9th Sep 2019, 2:55 pm   #6
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 877
Default Re: Philips 170A vs Mullard MAS281/15

Next a pic of the cleaned, polished and re-pinstriped cabinet. The detail of the new-style wavechange indicator is shown together with my mod to the selector shaft. The legends for LW/MW/SW on the old-style dial are on the right-hand side, same as the new-style, but instead all 3 are horizontal. They are revealed by a quadrant mask that rotates between the front dial glass and the rear white-painted diffuser. The quadrant mask rotates anti-clockwise, pulled by a wire cable attached to a lever fixed at right angles to the wavechange switch shaft. On the original switch, to suit the old-style dial, the wavechange shaft lever rotates from about 3 to 6 o'clock as it is rotated clockwise. In the most clockwise position (LW) the wire cable is at its maximum extension position and the quadrant mask is pulled down such that the upper edge is just below the LW legend allowing light to pass through. As the wavechange switch is rotated anti-clockwise one click to MW the wire pulls back up under the tension of the quadrant mask return spring, such that the mask edge now obscures the LW legend but a slot in its centre is now aligned with, and allows light to pass through, the MW legend. Continuing the same principle, the mask finally returns to its uppermost position obscuring LW and MW but the lower edge of the quadrant is now above the SW legend, which lights up. However, the new-style dial has LW/MW/SW legends that are no longer horizontal but are positioned at angles pointing towards their respective cursor scales, as shown in the pic below. The problem that this creates is that although the slot in the quadrant mask can still be used to illuminate the legends in turn, the rotation of the wavechange switch lever is now in the wrong sense and so LW is illuminated on SW and vice versa. The problem can be overcome either by swapping over 6 wires at the wavechange switch, or turning the shaft lever around so that it points in 180 degrees opposite direction. Even then I could not get the alignment right without fitting an extra pulley as shown in the pic.
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