The Marconi rheostat puzzle.
Up until about 1924 all valves in wireless receivers used the bright emitter. After that date dull emitters came into common use.
All receivers using bright emitters had a rheostat fitted in order to adjust the filament temperature of the valves.
This one valve Marconi also uses a bright emitter (Q valve) but has no rheostat fitted on the front panel!
The rheostat shown fitted on the side of the cabinet is of a very crude design and has no internal wiring to the valve filament. The valve has a 5 volt filament yet the LT voltage engraved on the terminals on the front of the cabinet is
6 VOLTS as you can see! The side rheostat terminals have been positioned to be exactly opposite to the 6 Volt terminals.
So it would appear that this rather crude rheostat is of Marconi installation as no other sign of a previously installed rheostat is to be found, the front controls just being,
FINE ADJUSTMENT and INTENSITY, the latter being the reaction control.
If this crude rheostat is not Marconi’s then surely they didn’t intend a 5 volt bright emitter to be operated from 6 volts did they? ...nearer to 7 volts with a freshly charged 6 volt accumulator !!
So what is the answer to this puzzle? If
you know I would appreciate your contacting me here with the answer.