From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparison of Bosch and Watford armatures, detailing windings, resistances, and magnet pole pieces.
| Identifier | WestWitteringFiles\S\June1928-August1928\ Scan119 | |
| Date | 22th August 1926 guessed | |
| Contd. -2- It will be noted that all the resistances and inductances of the Bosch armature are greater than those of the Watford. In comparing the two armatures before unwinding, what strikes one immediately is the incomplete way in which the Watford armature is filled, as compared with the Bosch. Another important feature is that the Bosch secondary winding is tapered all the way from the inner layer to the outer layer, the taper being more rapid towards the end. On electrical insulation principles this is certainly a desirable feature, and one which we have often felt should be incorporated in our ignition coils, did this not add to some extent to the expense of production. The Watford do not appear to make full use of the available winding space as in the case of the Bosch, and we think as previously stated that the total cross section of all the wires of the primary winding should be increased (i.e. either by greater section or more turns). The Bosch magnet pole pieces are symmetrically stepped, the (single) step being the same at all four polar edges, so that the cross section of the armature and pole pieces appears as in sketch:- | ||