On Fri, 10 Aug 2001, J.Feldhaar wrote:

> the cathode, the electron beam does not go towards the screen. Switching
> off the filament does not generate this electron cloud around the
> cathode, with the same result. Not heating the cathode may (I'm not
> sure, perhaps Roman can give a tip here) extend life.
>
  In any case shuting off the filament will not extend the tube life.
[ all modern TV's have keeped on the filament at 1/2 nominal voltage or
 less, all the time when are plugged in ]
I'm involved (more or less) in repairing garbages ( various tipes of
monitors caming here from all the world including US, Taiwan, Europe,
China, Japan as defective and not reparable )
The smartest types have a feature which shut at 1/2 the nominal
filament voltage when monitor is in stand-by and start with a
progressive HV value . The real problem comes when
the tube is supplied with HV ( 27 to 35 KV ). An important quantity of
emisive material which is deposed on the cathodes is trough away in the
switching moment ( and not the same quantity from all RGB catodes). If
there is no filament is worse on this moment. Ideally the order
in which the tube electrodes must be polarised are:
the filament, a sufficient delay to ensure heating, acceleratig and post
accelerating grilles, then HV and only then RGB cathodes ( contrast ), and
luminosity signals.
In reality all are suplied from the same HV transformer or from two
different transformers connected in cascade ( japanese models ).
Also, in time the filament become oxidable, and must be purged with a
simple HV discharging device.
The best way is to drop the old tube to the garbage. However a good
 tube may work at least 15 years.( see Toshiba, Sony or Philips tubes )
Never with Zenith ( americans ) or Chung Wha ( chinese ) tubes.
Vasile

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