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More S-40A stuff
I wrote a short time ago about the apparently reversed
band spread capacotor in my S-40A. Here is a bit more. First, for those who did not see the original thread, I found the band spread cap in my RX had the stop pin mounted in such a way that when the plates were rotated in the direction that normal dial string threading gave they went backwards. That is, the BS dial was at 100 at minimum capacitance. This is the reverse of normal Hallicrafters practice and does not match the dial, which indicates dial-set at 0. It was possible to get the capacitor, dial, and knob to run in the correct direction by crossing over the dial string at the capacitor drive pulley. I thought the pin had been removed and replaced by someone who wanted the BS dial to run from 100 as the BS does in most other makes of RX (but not Hallicrafters). With the help of Jeffrey Angus I was able to remove the pin (actually he did it) and replaced it with a roll pin facing the right way. When I went to restring the dial drive I realized that the diagram in the Hallicrafters handbook _and_ in the Rider's sheets was wrong, in fact, the stringing must be done in reverse of what is shown. I then discovered that the stringing information for the S-40 is more nearly what I had. Note that in the two sets of diagrams the capacitor pulley is shown facing in opposite directions. For the S-40 the opening in the flange is shown facing up and in the S-40A its facing down. In my S-40A it appears that the pulley itself was reversed when swaged on. This would match the reversed pin position. From the photos I've found on the web the type of band spread rotor is different in the S-40 and S-40A. The S-40 appears to have a single rotor plate for each section which is straight line frequency shaped (kidney bean shaped), and two stator plates, this is similar to the cap in the S-20R, which was the predecessor of the S-40 series. The S-40A has two plates on each rotor section and a single plate as a stator. The S-40B appears from the photos to have reverted to the single rotor plate type used in the earlier receivers. I am beginning to suspect that H my have gotten a lot of defective tuning capacitors and used them by reversing the dial stringing as I had to. My S-40A appears from various evidence to be an early one, probably made in the first run or in the first year of manufacture. One clue is the lack of a filament dropping resistor on the 6H6 noise-limiter and gas gate diode. This is absent in the Rider's sheets on the web, which are dated February, 1948, but is present in the Hallicrafter's Service Bulletin dated November, 1948. The latter indicates it is for Run No.3. My RX has an inspection stamp indicating Run No.1. At about this time parts were still in short supply and there was still some instability in the electronics industry, which was still recovering from WW-2. That makes me think that the explanation of the cap being defective may be correct. There may have been production deadlines to meet or financial considerations that prevented rejection of the parts. Its also possible that some got mounted on chassis before any error was discovered. In any case, it would be useful if others owning S-40A receivers would take a look at the capacitor in theirs and report what they find. In one web site with some H history on it its stated that all of H's business records were destroyed by the Wilcox Electric Co. when they took H over. Too bad since they would probably have held the answer to this, and probably a great many other mysteries. I also want to thank all those in this group who have been so helpful with this, and other, projects. -- -- Richard Knoppow Los Angeles WB6KBL |
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