6 Apr
2012
6 Apr
'12
10:57 a.m.
On 5 Apr 2012 at 19:42, Tony Duell wrote:
Right,,,
Over here, no TV sets were actually made suring WW2. After that war, I
think all sets had implosion protection (I've certainly enver seen or
heard of one that doesn't).
I have heard there were quite serious injuries caused to aircraft radar
operators in the war if the CRT imploded. Of course looking at a CRT down
a viewing hood (about 6" from your face) is rather different from
watching a TV at a noraml viewing distance, but I wonder if it was
decided based on that to fit protectio nto all TVs.
Hmm.. If it is an 'urban legend' then its
one that's spread through
many countries, UK, and European TVs all ahve some kind of implosion
protection too. And thais at a time when we didn't have
ambulance-chasing lawyers, The data books on CRTs from the 1960s (I
have a few) make it very clear tht you ahve to fit a separate
implosion screen if you use CRTs without implosion protection.
My issue with saying that implosion was a clear danger was that the
sheet of glass isn't present on all 1940s sets. Could the glass also have been intended for protection against the
soft X-rays
emitted at the CRT face? Remember this was the time when HV
rectifiers and even output tubes were customarily placed in a metal
cage.
I think X-rays prodeuced with an accellerating votlkage of 12kV to 15kV
are pretty much harmless...
Over here, the line ouptu valve (horizontal output tube), booster diode
(damper) and EHT rectifier (HV rectifer?) were often in a shield, but it
was a fairly light aluminium thing. Not going to be much protection
against X-rays. I think it was more an RF shield. It was rarely a
complete enclosure anyway.
With colour sets, the shunt stabiliser triode was something of an X-ray
emitter (it had 25kV from anode to cathode and pased about 1mA). That was
often shielded fairly wall.
As for the implosion screen, glass or perspex is pretty much X-ray
transparent unless it's doped wuth lead or similar. And I've never heard
it was. I've not seen any X-ray warnings about running the CRT without
the implosion screen (e.g. when servicing the set).
-tony