Not my usual start to a post as this is a repair as opposed to a restore.
This set was restored some time back by me but had developed a collapsed frame, testing showed the grid of the SP41 frame output valve was shorted, the main suspect was the shielded coax type cable feeding the grid. This was duly sorted today with some network coax (I knew it had other uses) and its fine again.
So to the question I need to ask is, when the set is on test on the bench I happened to touch the face of the tube and was surprised to see the picture expand to the touch, almost like I would be touching a touch screen. I have never seen this before and its nothing to do with my repair so what is the possible cause ?
So the same principal as a plasma ball really, that makes perfect sense.
Thanks, at least it can be boxed up again without needing to delve deeper.
My Ferguson 992T does this.
First time I came across this was in my early days of the trade (early 70's) when 405 was on the decline. We used to get a fair number of 405 only sets that were used a 'second' sets in bedrooms. I remember cleaning a filthy screen on one set then switching on to find one corner of the picture looking very strange...sort of squashed and twisted but it was 'uncurling' before my eyes. When I touched the screen at that point, the picture moved and expanded out to normal. Some sort of static charge I suppose. Some sets were worse than others and some were unaffected.
The contrast screened cable was going the same way with severe cracking so that has also been replaced.
Just prior to me boxing the chassis up again last night I had a play with the brightness, advancing well past a viewing level whilst looking inside the tube through the clear rim showed up a galaxy of little phosphor specs in the tubes flare just before the neck, looked very pretty but not visible at normal brightness. Must have had some splash back from the phosphor coating 
Another question, does capacitor C41 have a technical term/name?
... Another question, does capacitor C41 have a technical term/name?
Decoupling would be my first choice ...
When all else fails, read the instructions
Another question, does capacitor C41 have a technical term/name?
I think it's called FRED. Flaming Ridiculous Electronic Device
You can tell the heat's getting to me.
Warning !...Jeffrey has failed his "PAT" test.
His "Penguin Ambient Temperature" has overloaded ! 
OK I'll exit stage left 
Marc.
Marc
BVWS member
RSGB call sign 2E0VTN
Oh dear we have wobbly penguins.
