Pye VT4

[Freya]

Thats a really neat solution, well done

[Murphyv310]

Hi.
There are some issues with the modification. The main issue is the flyback time is too long so the picture information appears in the flyback giving foldover on both sides. I think this is due to the 400pf tuning capacitance. On previous mods to 70 degree CRTs using a jellypot I reduce the HT to the line stage and this gives a good compromise between EHT and width without foldover. This issue here is I'm using a 625 line TX on 405 so it needs more tuning but that is counterproductive.
So I have rewired the scan coils from series connections to parallel, this gives more width, removing the tuning brings the width in but still with overscan and high EHT, reducing the HT to the line stage gives correct width without foldover but only 11kv EHT, the idea then is to fit the width control back into the set and increase EHT for 12-14Kv and then adjust the width.

The other issue to show up is those dodgy height and linearity pots, the slider can short to the centre reducing scan which I need to attend to.

[Murphyv310]

Hi.
Well today I completed the mod to the line output stage.
I now have the 1500, 625 line Jelly-pot installed. The Tuning capacitor is 100pf and the HT to the line stage is dropped by a 500r resistor. This gives me full width, 14Kv EHT and 510v boost. the G2 of the CRT is at 330v WRT Chassis and the focus around 180v WRT Chassis. A supplementary transformer is between the LOPT and the reference phase splitter transformer which is part of the VT4 circuitry.
The Frame linearity pot was leaky and has been replaced. This is of importance to anyone restoring a V4 or VT4 as this fault is hard to diagnose, you get very little control over linearity and the height control just makes the picture stretch badly, If you get stuck with that problem then loosen the controls securing nut lifting the control from the chassis will make the height jump up if its faulty. the leak can be a full short circuit to up to a few meg ohms.
I still need to do other things to the set but so far I am well pleased.

There is some overshoot on screen plus the line jitter still occasionally shows up, I still might try and do away with the supplementary transformer but I now need to get back to the D16T.