04-05-2017, 08:11 PM
(This post was last modified: 04-05-2017, 08:12 PM by Geordie McBoyne.)
Hi Trevor,
This set was subject to one of the most comprehensive list of modifications I've even seen done to a television receiver. You are absolutely correct, more than sixty years ago an unknown engineer put a lot of effort into redesigning the signal circuits of the 1804 and even if we don't what the motives were for doing all this work we owe to him to preserve the set in it's modified state.
Other additions to the original 1804 circuit will be retained. The Pye "positive interlace filter" will be wired into the main chassis instead of that module thing which used an EB91 double-diode. In the 1804 V8 is a Marconi-Osram D63/6H6 double diode and in the original EMI circuit only one section is used for the interlace filter, this valve can be rewired to function in the twin diode interlace filter circuit. A vision interference limiter was in fact an official EMI modification but the method employed by EMI left much to be desired. According to the service manual a degree of loss of picture definition would have to be tolerated after the white spot clipper was added. The method employed by the mystery engineer is better.
New HT electrolytic capacitors were delivered today and these will be fitted in due course.
Geordie McBoyne.
This set was subject to one of the most comprehensive list of modifications I've even seen done to a television receiver. You are absolutely correct, more than sixty years ago an unknown engineer put a lot of effort into redesigning the signal circuits of the 1804 and even if we don't what the motives were for doing all this work we owe to him to preserve the set in it's modified state.
Other additions to the original 1804 circuit will be retained. The Pye "positive interlace filter" will be wired into the main chassis instead of that module thing which used an EB91 double-diode. In the 1804 V8 is a Marconi-Osram D63/6H6 double diode and in the original EMI circuit only one section is used for the interlace filter, this valve can be rewired to function in the twin diode interlace filter circuit. A vision interference limiter was in fact an official EMI modification but the method employed by EMI left much to be desired. According to the service manual a degree of loss of picture definition would have to be tolerated after the white spot clipper was added. The method employed by the mystery engineer is better.
New HT electrolytic capacitors were delivered today and these will be fitted in due course.
Geordie McBoyne.
