22-11-2017, 12:46 AM
Hi Trevor,
After reading about your Murphy V659 I'm spurred on to take another look at my V683DX.
Like your V659 my set has the same fault whereupon after 15 minutes or so the width comes in and at the same time the EHT voltage is reduced. The low EHT causes the picture height to increase. Also, the picture is slightly folded over at the left side of the picture.
So before replacing the line output transformer the line oscillator and line drive conditions should be reinvestigated.
Link to the UKVRRR: https://www.vintage-radio.net/forum/show...p?t=104681&highlight=Decca+DR123+dual+standard+TV The substitution of the orginal line output transformer with a BRC jellypot. Of particular interest is post No. 19. It was found the mark space ratio of the line drive was correct on 625 lines, on 405 the mark space ratio was 27:73, far from ideal. A modification to the line oscillator improved matters considerably. See second attachment.
The line drive is closer to a square waveform.
Geordie McBoyne.
After reading about your Murphy V659 I'm spurred on to take another look at my V683DX.
Like your V659 my set has the same fault whereupon after 15 minutes or so the width comes in and at the same time the EHT voltage is reduced. The low EHT causes the picture height to increase. Also, the picture is slightly folded over at the left side of the picture.
So before replacing the line output transformer the line oscillator and line drive conditions should be reinvestigated.
Link to the UKVRRR: https://www.vintage-radio.net/forum/show...p?t=104681&highlight=Decca+DR123+dual+standard+TV The substitution of the orginal line output transformer with a BRC jellypot. Of particular interest is post No. 19. It was found the mark space ratio of the line drive was correct on 625 lines, on 405 the mark space ratio was 27:73, far from ideal. A modification to the line oscillator improved matters considerably. See second attachment.
The line drive is closer to a square waveform.
Geordie McBoyne.
