8 Apr
2012
8 Apr
'12
11:29 a.m.
On 7 Apr 2012 at 19:42, Tony Duell wrote:
No, the primary reason for aluminising the screen was certainly to
prevent -ve ions (from residual gas in the CRT) from damaging the
phosphor .This was a real problem at one time. The ions were not
deflectred much by the magnetic defleciton system (they would be by
electrostatic defleciton plates IIRC), and you ended up with a dark spot
at the centre of the screen.
I guess few people remember fitting and adjusting the ion trap magnet on
a monochorm TV set...
I've found an old Mazda databook. This has nothing to do wit hte car
company, it states that 'Mazda Cathode Ray Tubes are manufacutred in
Great Britain for the British Thomson-Houston Co, Ltd, London and Rugby,
and distributed by The Edison Swan Electric Co Ltd'
Anywy, this book contains data sheets on 3 CRTs, CRM71, CRM91 and CRM
121. They are very similar apart from the screen diameter which is 7", 9"
and 12" respectively. These are circular-screen magnetically defelcted
CRTs for TV applications, and if what I think is a date _is_ a date, the
data sheets were printed in 1942 (which does suprise me a bit).
All 3 data sheets contain a paragrpah simular to the following (obviously
the type number changes) :
'The handling of the CRM71 tube in transportation, storage and use
requires car, because the tube may be broken if subjected to sudden jars
or excessive strains or, if abused, the tube may be weakened so that it
may subsequently implode owing to the pressure on the tube due to the
vacuum within. The equipment in which the cathode ray tube is utilised
should be designed to prevent the bulb from being damaged and to protect
the user from the effects of an implosion if the bulb is damaged or has
been weakened in prior handling. The screen of the tube should be covered
with a plate of safety glass, and googles worn when handling the tube'
Now, thoughts.. .THis is round screen CRT with a noticeably convex screen
(commonly known a sa 'goldfish bowl' over here ;-)). SUch a screen is
stronger for a given glass thichness than a flatter one, so the glass
could be a lot thinner than on a more modern CRT. THis may mean it's more
liable to fracture into sharp fracgments that fly.
Thre is not integral implosion protection on this CRT.
And the nrequirement for having implosion protection was noted quite
early on (if my interpetation that this was printed in 1942 is correct).
-tony
2) It acts as a light reflector, so most of the
light emitted by the
phosphor comes out of the front of the CRT. No point in wasting it by
illumninating the inside of the set :-)
I think that's probably it. A couple of datasheets out of HB-3 would