Murphy V659 Astra Chassis

[Murphyv310]

Hi.
I've been the owner of a V659 for some years, it was a cast off from HKS (John Wakely). It has always had some line timebase issues and I spent a lot of time on it a few years back. It has been sitting on my big 21 inch Ekco Console for around 3 years.
I have been thinking of doing a LOPT transplant on it and have two options a Thorn Jelly pot or an Ekco type from a 17 inch 110 degree chassis.
To add to this I have tried two Murphy oil filled transformers in the set with the same symptoms.
There is fold over on the left hand side, it varies dependent on what Aurora I am using on 405 lines. I did try it on 625 at one point and it was dreadful.
Today though I rechecked everything very thoroughly as I still had a sneaky feeling it wasn't the LOPT at fault. Line drive was 110v p-p on the scope but the "ramp" looked a different shape to the one shown in the manual. After going through the oscillator again one resistor I could see was original. R328 a 1K on the cathodes of the 6/30L2 line osc had risen to 1.25k, out of spec as it is a 10% resistor, I wasn't convinced but a new 5% resistor was fitted and immediately the drive rose to 130v P-P which is spot on, there is little king in the ramp up of the waveform but I think this could be a reflection back from the output stage, possibly pick up or a boost cap down in value of even one of the chokes on the U193.
The foldover has lessened on two of the Auroras and on one there is now nothing, EHT seems a bit low but it holds up now after an hours running.
Next is to test 625.                    

[Geordie McBoyne]

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.