09-06-2017, 09:38 AM
(08-06-2017, 08:27 PM)Terry Wrote: The main differences were between battery only sets with 1.5V cells supplying parallel filaments and mains/battery sets which usually arranged the filaments in series, fed by a 7.5V battery.
Well, I did say usually!
Looking at the diagram in the link that Mike posted, Grundig opted for the parallel filament 1.5V* arrangement in this set.
* Not quite true as, although this is the marked voltage on the cells as sold, this (and slightly higher levels) are only produced for a short time, the output then settling down to around the 1.4V mark for the majority of their life. Thus the valve data always specifies a filament voltage of 1.4V.
It is normal to run these valves at a slightly lower voltage - the Grundig figure is 1.35V - which helps to prolong valve life as they have to function at voltages even lower than this as the cell voltage drops even lower towards the end of their life.
