Time to resurrect this old thread -- we were previously discussing here about how the Inductuners in the Dumont RA-103 and its clones seem to come in two flavors -- one with a dial that has channel numbers increasing in the clockwise direction, and one with numbers increasing in a counterclockwise direction. Very strange!
This appeared to suggest that Dumont had Mallory make two different types of roller inductors with opposite helix directions, for no apparent reason.
Finally figured out why. The basic Inductuner roller inductor is identical in both types of tuners, but the shaft gearing is different. Here are the two variants:
Version A has a direct shaft from the roller inductor out through the front panel, with a reduction gear for the slower rotating of the two concentric dials. Version A looks like this (from my Crosley 9-407, photographed several years ago). Note the side-facing tubes on the right side of the tuner chassis.
In the above picture, the shaft is actually broken off (more on that later). In the picture below is the Inductuner after it was repaired several years ago, and with the cover removed. Direct shaft clearly visible.
Version B does not have a direct shaft out the front panel, but instead has a gear drive, which reverses the sense of rotation and is the reason why the two versions have clockwise vs counterclockwise dials. Note that this version has upright tubes on the tuner chassis. This is from the Dumont RA-103 I'm working on now.
Here's a closeup with the dials removed, showing the reversing gear.
What's interesting here is that to get the shaft location to be the same for both models (the cabinet is identical for both, with the same dial and tuner shaft position), the whole mechanical layout of the tuner chassis has been redesigned! The reversing gear moves the shaft to the right and higher, so the chassis was modified to move the whole Inductuner subchassis down and to the left.
Why in the world did they do this? I have a hunch it relates to the broken shaft. With the shaft of the Inductuner sticking directly out the front of the set with a big knob on it, the ceramic Inductuner shafts were getting broken in shipping and handling by pressure being put on the big tuning knob. So eventually they redesigned it so that the Inductuner shaft did not protrude directly out to the big knob, but rather a sturdy shaft driving a gear did so instead. This probably helped prevent damage to the Inductuners.
I don't know if that's really the reason, and I don't even really know which model was first and which was second, but now it's clear how the two designs differ. The roller inductor is the same in both models, but the drive shaft arrangement and tuner chassis design is very different between the two.
Mystery solved.
But, to finish restoration of this set, I still need either:
- nice set of dials for the gear-drive tuner in the set, which needs a dial which shows numbers increasing in the clockwise direction when looking at the static dial (turning dial clockwise goes towards channel 1), or
- tuner with direct shaft (like the Crosley set above) that can use the nice dial I have, which shows numbers increasing in the counterclockwise direction when looking at the static dial (turning knob clockwise goes toward Channel 13).