Picked up this shoebox-sized resistance box at the MIT Flea Market today for $40. The guy who sold it to me had a 5-decade version as well (at $50--it's $10/decade, you see) but I went for this one since I felt OK gambling $40 and it was in better shape over all. In fact, it looks close to new.
A search on-line turned up documentation dated 1954. Today, IET/Genrad carries a model 1433, so it looks like this model could have been in production a long, long time.
A peek inside turned up custom wound resistances, with the 1-, 10-, and 100-ohm steps made from "Ayrton-Perry" wound on molded phenolic forms and the 0.1-ohm steps made from "bifilar" wound with ribbon. The 0.1 steps are rated at 0.25W and +/- 0.5% accuracy; the 1-ohm steps at 0.6W with +/- 0.15% accuracy and the 10- and 100-ohm steps are also 0.6W and have 0.05% accuracy. There was no tale-tale smell of overloaded resistors and the switch contacts looked clean and well-lubricated, so it seems the seller's promises were all true. And, it tests out spot-on with my Fluke 87V ohmmeter, but since its accuracy exceeds that of the meter, I can't really judge if it's really in calibration. Not sure how in the world you would adjust it if it weren't!
Even if somewhat limited in its range and certainly much bigger and heavier than the new IET resistance boxes, this turned out to be a great find and bargain.
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