"Cydrome Leader" wrote in message
...
Ian Field wrote:


"Phil Hobbs" wrote in message
m...
On 03/07/2014 03:13 PM, Cydrome Leader wrote:
Ian Field wrote:


"Cydrome Leader" wrote in message
...
Ian Field wrote:


"Cydrome Leader" wrote in message
...
Ian Field wrote:


"Leif Neland" wrote in message
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F?lgende er skrevet af Phil Hobbs:

When I was a kid, I used to get dead TVs and take them apart for
the
components. To get rid of the picture tubes, I put them in a
Rubbermaid
trash can and shot out the faceplate with my slingshot.

As a kid I unwrapped the capacitors to find the interesting stuff
inside
all that wrapping paper. Never found anything, though... :-)

When I was a kid, someone gave me a regen set in a very grand
wooden
cabinet.

When I'd finished breaking it - it was time to take it apart and
see
what's
in it.

In a compartment under the one the chassis was in, there was a
huge
flat
profile paper capacitor - one that big could only have been the HT
reservoir.

Think of all the things I could've got up to with that if I hadn't
unraveled
it!

I dragged a huge transformer out of a TV set to grade school once
to
show
people the huge sparks that could be drawn off one winding with a 9
volt
battery. It was actually a fairly fat and impressive arc. The
transformer
was eventually confiscated. Boo.

Those old mains derived EHT transformers were probably even more
lethal
than
a MO transformer.

For a B&W TV, 6 - 7kV was about average - not sure whether any CTV
ever
had
mains derived EHT.

It was some sort of large gooped up with tar EI core thingy with one
super
high inductance winding. I still have no idea how it worked in a
television. If they made 6-7kv was there then some sort of diode and
cap
multiplier to run the CRT?

AFAIK it was just half-wave rectified, the peak value whatever that
was,
ended up at the final anode.

Its a bit surprising when you think that generally, CRTs were long
narrow
defection jobs - some early homebrew sets had electrostatic
deflection,
maybe a few commercially produced sets too.

Is this why tubes like in oscilloscopes, which are electrocstatic are
so
long for their screen size? My current scope doesn't have the hump in
the
back for the end of the tube, but I suspect it's a normal CRT with a
yoke
and coils as well, since it's really just a small computer monitor.


Electrostatic focusing is much faster than magnetic, but not nearly so
well controlled--you get a lot of aberrations, which grow very rapidly
with deflection angle. The basic issue is that electrons that are closer
to the plate get bent further than those further away. In an optical
system, you can correct for this by using a combination of positive and
negative lenses, but there's no such thing as a negative electrostatic
lens.

It was a real parlour trick getting decent vertical linearity and good
spot sizes with pure electrostatic deflection.

Speaking of optics - I remember a PC monitor with a slightly concave
faceplate, that was a pretty substantial slab of glass, the things
weighed a
bloody ton!

Was it possibly one of those Zenith flat CRTs that really did look
concave? They were really weird looking, powered on or off.

Now you mention it I think they were zenith - there was a sort of flurry of
people wanting them repaired, then they dried up as if they'd never existed.

Not long after that, CRTs in general went out of fashion.

I didn't miss those flat screens - they were bloody heavy!