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Re: PMT drift

Larry Anderson writes:

>The procedure that Seamus O'Kane mentioned in his most resent posting I 
>believe is a good one to follow. Placing a piece of negative in the gate 
>will reduce the amount of light reaching the PMT's and prevent heating of 
>the PMT dynodes and anode.

We use a black card for this purpose, shutting off all light to the PMT's
during standby periods. Is this preferable, or is there some benefit to
allowing some light to pass?

Seamus writes:
>The other area that presents problems is the shading. We are using the
Pogles to
>store base offsets
>that bring the Golds auto alignments back to even shading but these can have
>be changed dramatically if we run Inter Pos stock for instance.

We have also found that Ursa Gold shading can be problematic in some cases,
especially with I.P.  I have just recently had success using manual shading
for the first time, eliminating the annoying Ursa "green on one side, magenta
on the other". I can't yet vouch for the repeatability of this procedure,
since I was able to go from programming to laydown without having to
autoalign (after initializing the new shading setup). Is anyone else using
this feature more extensively?

David Bernstein
The Post Group