Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!hess
From: hess@iuvax.cs.indiana.edu (Caleb Hess)
Newsgroups: comp.sys.next
Subject: Re: Screen Saver
Message-ID: <16992@iuvax.cs.indiana.edu>
Date: 30 Jan 89 21:22:45 GMT
References: <653@wucs1.wustl.edu> <6207@polya.Stanford.EDU> <1476@neoucom.UUCP>
Reply-To: hess@iuvax.cs.indiana.edu (Caleb Hess)
Distribution: usa
Organization: Indiana University, Bloomington
Lines: 24

In article <1476@neoucom.UUCP> wtm@neoucom.UUCP (Bill Mayhew) writes:
>
>It seems as if it wouldn't be too difficult to be able to switch
>off the horizontal drive circuit while the screen was blanked; it
>would only require one transistor, and the same register bit for
>beam control would suffice.  It would be a lot safer too, as the
>risk of a fire in the power supply would be elimiated while the
>monitor was unattended.  Note that the CRT heater could remain
>turned on, so there would be no obnoxious lag when the screen was
>reenabled.
>
>--Bill

I would hesitate to implement this change without careful consideration of
all the implications.  In a previous life as a broadcast engineer, I learned
that the lifetime of a vacuum tube run as a 'hot spare' (with filament on
but no anode voltage) is usually much shorter than the lifetime of a tube
in normal service.  It seems that the hot filament poisons itself if the
electrons are not sucked away as they boil off.  In the case of RF power
tubes, this meant that the tube couldn't deliver normal power because of
insufficient cathode current.  In the case of a CRT, I would expect a loss
of brightness due to the same effect.

hess@iuvax.cs.indiana.edu				KE9LC