More S-40A stuff
On Thu, 02 Apr 2009 10:52:03 -0700, Richard Knoppow wrote:
[snip] 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. Just to continue with the speculation, it's conceivable that Hallicrafters got exactly the tuning caps they wanted. A reverse rotation bandspread cap works well enough in the S-40A and the reverse rotation cap might have been necessary in some planned S-40 variant. [snip] ? 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. My S-40A has the reverse rotation cap. If I recall correctly, it has the 6H6 resistor. I can't check it out right now, but I should be able to within a couple of weeks. Frank Dresser |
More S-40A stuff
"Frank Dresser" wrote in message ... On Thu, 02 Apr 2009 10:52:03 -0700, Richard Knoppow wrote: [snip] 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. Just to continue with the speculation, it's conceivable that Hallicrafters got exactly the tuning caps they wanted. A reverse rotation bandspread cap works well enough in the S-40A and the reverse rotation cap might have been necessary in some planned S-40 variant. [snip] I don't think so. The knob, dial, and capacitor should all rotate in the same direction. The dial must start at zero beacuse that's the marked "band set" point, the capacitor must set at minimum capacitance for the main dial calibration to operate within the adjustment range of the trimmer caps. The S-40A band spread capacitor differes from the one used in the other S-40 models and in the S-20R, which was the predecessor to the S-40 series, in that its got symmerical band spread plates, the others have straight line frequency plates. This means the rotor could rotate in either direction and still have the same "law" of capacitance variation with angle. The others _must_ turn in one direction only. One of the things I noticed is that the poistion of the opening in the flange of the main pulley as shown in the stringing diagrams is reversed in the S-40A from the position shown in the S-40 diagram. Usually, stringing diagrams are shown for the dial being at one end so that when you wind on the dial cord you have the stop to work against. This is not the case in my RX. So, I think both the stop pin _and_ the pulley were put on wrong. One can speculate about why this was done. You may be right that H specified these caps for some variation of the RX but never made it. But, keep on mind that parts were evidently in short supply when the RX was made so perhaps the caps were used and the dial string crossed over as a work-around. Note that one of the power resistors was made up of two resistors in parallel, this is mentioned in the parts list as a possibility so I am pretty sure it came from the factory. It suggests that H could not get enough of some parts and had to resort to work-arounds to meet production committments. Again, apparently all Hallicrafters business records were long ago destroyed so one can only guess. If someone has an original insruction manual the photos may be clear enough to see how the cap is rigged, the stuff on line is too low in resolution to show this. I wanted others with S-40's of various types and vintages to have a look at what is actually in them. What I am curious about can be seen by just lifting the lid and seeing in wich direction the band spread cap moves in going from minimum to maximum. This is all probably quite trivial in the scheme of things but sometimes its the seemingly trivial things which are the most interesting:-) -- -- Richard Knoppow Los Angeles WB6KBL |
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