Quote:
Originally Posted by Tube Radio
Anyways about three years ago while using the scope the 5ADP1 CRT in it lost all ability to focus properly. I then tried several 5ADP* series CRTs all with the same problem, yet a 5CP1 works properly.
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A few questions here:
1. You tried several 5ADP* CRTs .... how many? ... you
might have a couple of bad tubes, but as the number goes up, the likelihood of them
all being bad in the
same way decreases dramatically.
2. Perhaps the operating specs for the 5CP1 are slightly different ?
3. Do you have a schematic for the scope?
4. Does the focus pot have any effect? Do you have to set it to one end or the other for "best" focus?
My best guess for now, is that one of the resistors in the HV divider string (which includes the focus pot) changed value while you were operating the scope, and a 5CP1 works ok with the changed conditions.
jr