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Old 20th Jun 2018, 9:33 pm   #7
PJL
Dekatron
 
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
Default Re: Marconiphone Type 41

I have now started the strip and fix. It is filthy and needs all of the screw contacts tidied up before I move on to coil winding.

The first problem is there are two variable resistors and both are open-circuit as in the conductive surface no longer conducts. One still seemed to have an original paint seal so the carbon has probably just aged and fallen off.

I have a horrible feeling that they were 'made to measure' by applying graphite to the surface and of course I have absolutely no idea what value they were! They both attenuate the signal by applying a resistance across coils so do not carry any DC current. So, if we assume we do not want the resistance to mess up the Q too much when set to its highest level, what should I be aiming for? My guess would be quite high?

I am thinking I may leave them out of circuit and try a few fixed values before I have a go at putting carbon back with a pencil. They are superbly made with spring loaded carbon contacts.
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