Derwent 9" television
I`ve been restoring this late 40`s early 50`s set and it shows a descent test card but the trouble is the line hold pot gets hot.
After the chassis has been running for half an hour , the area of the chassis where the pot is secured to gets warm and I think if it were not attached to the chassis frame it would get to hot to touch.
Now I didn't think pots were suppose to get hot like this.
When I first started on this chassis there were 3 wire wound resistors open circuit that had corroded and the wire unravelled .
I calculated there resistance by measuring the good part of the resistor that had not unravelled and fitted the values shown in the circuit diagram.
These resistors are the 6.8K screen feed to the EL38 , the 1K series resistor to the line hold pot and the 560K off the width coil.
I used a carbon type for the 560K.
I had calculated the resistor in series with the line hold pot to be 3 to 4K but I could only lock the picture by using a 1K so this is why i`m thinking something isn't right.
I don't have a circuit diagram for this set and the fact that Derwent made and maintained there own sets, I doubt that a diagram exists. To enable you guys to offer help I drew the diagram below.
The HT line is 256v and the 6.8K puts 75v on the screen of the EL38 line out put valve.
The Plessey mk1 chassis is similar and this is on trader sheet 984/T10.
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