[Electrical]

Hi Humphry
I am pleased to see you have your tester up and running.
With reference to the shape of the spot, I wondered if you have set the focus pot (POT ‘E’) on the front of the instrument, it could; affect the astigmatism of the spot if it is not correctly set. The ‘Test Mains’ card is used to adjust the testers mains transformer to the supply voltage to the nearest 2V tapping on the ‘Mains Adjust’ selector switch and the spot on the CRT screen will move up and down the screen with mains voltage fluctuations. The spot moves about 5 to 6mm for a 2V change in mains input and is adjusted to be as near as possible to the dotted ‘A’ line.
Where I live the mains voltage varies all the time, from a low of 218V to a high of 252V, which is well within the nominal 230V + or – 10% supply voltage. To overcome the supply variation I now feed my tester via a Claude Lyons AC Voltage Stabiliser. The output is set at 230V so the ‘Mains Adjust’ selector switch is in the middle of its range, this particular stabiliser is a very sophisticated servo controlled saturable reactor type and can maintain the selected output voltage over a + or - 16% mains input variation. However I have been told that a simpler version this type of regulator is still used on the continent.

Regards Stan.