Thanks. The CRT's brightness is fine. It's the focus that is soft and is most noticeable in the corners. I'll have a look at the schematic and get my bearings on where the focus resistors are and replace them and see if there's any improvement.
toggle quoted message
Show quoted text
On Sun, May 18, 2025 at 07:29 PM, Mark Vincent wrote:
As for the crt being weak/borderline, you can increase the heater voltage
20-30% higher for some minutes to see if that helps. This step is done without
the scope being on, only a supply that is higher than 6.3V. If you have or
access to a crt checker that is good to professional quality, you can check
it. Crt checkers have different heater voltage selections so the previous step
can be done with a checker. If weak, replace with a known good one.
There are resistors in the focus circuit and a few on the high voltage board
that are known to go bad to being overstressed. They are the ones from B+ to C
and C to B on the collectors. Use 1W 1% types, get ones that are physically
correct for 1W such as 4x10mm or so, to replace the 1/4W types. These
resistors will go high/open making it look like poor focus or a weak crt. The
100meg 1/4W carbon on the high voltage board, replace! That will be way out of
tolerance. Ohmite has a blue body radial type that will directly fit that is
larger in wattage or you can get 1% 1/2W axial from Mouser.
