06-04-2014, 09:53 PM
(This post was last modified: 06-04-2014, 09:54 PM by Radio Fixer.)
Its strange that the Groom in 1941 is still using a field coil speaker when Philips was using PM in the early 30's. By post war you would have thought everyone would be.
In the early days when electrolytics were difficult to make, in large values then the series field coil was useful as it acted as a choke as well. But later then caps of 100 mF, as the Groom, were around and shunt field could be used. The shunt field has the advantage that the rectifier has load across it all the time making high rises of voltage across the electros less likely before the O/P valve warms up or if someone pulls it. But why would you want to wind thousands of turns of wire? I suppose for some it was still the cheapest way as access to high grade material for the magnets was in short supply.
Gary
In the early days when electrolytics were difficult to make, in large values then the series field coil was useful as it acted as a choke as well. But later then caps of 100 mF, as the Groom, were around and shunt field could be used. The shunt field has the advantage that the rectifier has load across it all the time making high rises of voltage across the electros less likely before the O/P valve warms up or if someone pulls it. But why would you want to wind thousands of turns of wire? I suppose for some it was still the cheapest way as access to high grade material for the magnets was in short supply.
Gary
