3 Apr
2012
3 Apr
'12
3:26 p.m.
On 04/03/2012 04:07 PM, Tony Duell wrote:
Your belief is not a factor, you didn't work for DEC.
Rod and I both worked for DEC, I also worked with the terminals people
during the Vt220, VT24x and VT320 series. DEC actually did interact
with CRT designers to get the exact product they wanted to DEC
specifications.
I'm old enough to rember and worked on old tVs that didn't have such
a safety layer. It was never an issue. For sport my brothers would
take the
tubes (CRT) from junkers and haul them out back where they would
stand back 20-30 feet and pelt them with rocks. I've observed they
can be quite robust fromt he front but quite fragile from the neck side.
It had to do with acceleration voltages and part since the added glass was
leaded to meet EU/TUV standards for X-ray radiation.
Since DEC shipped to the major 13 markets they had to meet all their
standards. Not all made sense to us here in the USA but you do this to
sell things.
Some countries mandated specific eronomics and therefore allowable
colors, brightness, contrast and many more things. Often a cable that
was
correct in 10 of the 13 majors was disallowed because of the cordage
or colors used didn't meet the local rule. Ignoring the wall mains
connector
the cable itself was a often 13 differnt cords because of internal
construction.
So cables it was easy to be destination specific but for a thing that was
used/manufacured in great quantity the standardized design was the rule.
DEC even had internal standard for designing for international sale and
it required all products (with exceptions) to meet internationalization
requirements.
Still dangerous as the mains line can still be intercepted. You do
learn to behave well
to live long.
Back inthe day things were not always safe or smart, then again the people
working with it often were smarter. However, libility being what it is and
various govenments decreeing safety standards allowed both stupider
people to survive and to protect the unwary.
I alwas felt that anything mains powered without isolation was designed to
kill anyone trying to repair them. Sort of the first generation
"No User Serviceable Components Inside".
Allison
All well and
good. One tiny point. I worked for DEC Terminals Product Lin=
e
when those items where in current production.=20
I could counter that by saying that while you may well hvee(SP?) designed
things that used said CRT, and may have handled the CRTs for many years,
this does not mean you know exactly how the CRTs themselves were
designed, and whether they remain sade(SP?) if you remvoe(SP?) the front glass layer
I don't beelvie DEC designed the CRT, they bought it in. I am nto(SP?) even
sure all came from one manufacturer, in which case it may well be that
some CRRTs(SP?) are safe without the outer glass, some are not. _I_ don't
know, and I'd rather not be showered in glass fagments to find out.
The tubes were
just fine without the face plate and met all implosion
requirements. Some (Green I think) did not have them at all.=20
Interesting. I am
suprised there are any differentces(SP?) between the CRt(case)
other than the phosphor. Why was this? Did all colours of CRT come from
the same manufacturer?
It probably is safe to run the CRT without the outer glass sheet, and I am
sure you know what you are doing.
However
certain national safety specifications required the second screen
and its anti splinter layer. This was regardless of if the underlying tub=
e
Now tha I can well believe :-). My experience of safety requirements is
that there are often hoops you have to jump through for no good reason.
How did the green CRTs get roudn this (or were monitors/terminals fitted
with said CRTs simply not sold in such countries?
met the
implosion spec. The spec was that it was present and its material=
s
met the requirements.=20
I think they put them on all the white ones to save having two different
cases.
I am perhaps a bit over familiar with the way I handle CRT's. However in =
I
am perhaps too far the other way. My father spend much of his working
life working with UHV systems (and to be fair, the forces on the
envelopedon't really change that much as the vaccum gets harder...) and
had a few things implode. He warned me to take great care...
the
time when I was a student apprentice in the 1960's I did work in a High
Voltage test lab (Anybody for a bit of 500KV?) and the guy I worked for h=
ad
been part of the original EMI television development team in the late 193=
0'.
Guess who got stuck with mending cranky 1950's TV's with live chassis?
Been there, done that... It wasn't so bad on the valve sets with half
wave rectificions, with a bit of care you could ensuee(SP?) the chassis was
connected to the neutral side of the mains [1] and thus be relatively
safe. The later IC-based sets with bridge rectifiers were worse,
whichever way round the plug was connected, the chassis was live.
[1] A common way to do this was to use one of those neon tester
screwdrivers which would light up if touched on a live chassis. If so,
revese the mains conenctions. A _NOT FUNNY_ 'joke' was to convice the
newbie that if he took his screwdriver apart and turned the neon round,
it would then light on a dead chassis. (Of course it does no such thing,
it still lights on a live one).
"Isolation Transformer Rod? What do you want one of those for?"
The
serivec(SP?) information for the PSU in one of my Philips machines
includes all the waveforms round the chopper circuit. This is a SMPSU
with a mains bridge rectifier. The instructions for obvserving these
waveforms tell you to use an isolating transformer, or if this is not
available to disconenct(SP?) the maisn(SP?) warth(SP?) wirew(SP?) in the 'scope mains
plug.
Err, i have this slight objection to a 'scope with a live cabinet :-)