In article ,
"FranK Turner-Smith G3VKI" wrote:

"Jerry Stuckle" wrote in message
...
On 2/20/2014 4:15 PM, Brown Sugar wrote:
On 19/02/2014 18:51, Jerry Stuckle wrote:
On 2/19/2014 1:35 PM, Frank Turner-Smith G3VKI wrote:
On 19/02/14 03:09, Jerry Stuckle wrote:
On 2/18/2014 7:06 PM, FranK Turner-Smith G3VKI wrote:
"Jerry Stuckle" wrote in message
...
On 2/18/2014 4:29 PM, Percy Picacity wrote:
In article , Brian Reay
wrote:
On 18/02/14 20:31, Jerry Stuckle wrote:
There was a time, back inthe 1920s and 1930s, that any active
device
(valves in them thar days, tubes for the leftpondians) would
cost nearly
a week's wages for the average working man, and so it was good
economical
sense to try and use it as many ways as possible
simultaneously.
Times have changes, and active devices with performance into
the
tens
of MegaHertz are now ten-a-penny, so what is achieved by
competitions
such as the "Two Transistor Challenge" where it is the costs
of
switching (manual, relays) which would be the major outlay?
Not carping, just curious.

There have always been "contests" like that, though sometimes
they were
about "build a whole receiver using the same transistor
type", or
"build a receiver without any ICs" after ICs had come around.

What I find intriguing is the realisation that valves ("tubes"
to
you?) can be operated with only 12V on the anode.

No unusual at all.

Not only were a number of valves for the car radio (and possibly
other)
markets available, I recall designs which use 'ordinary' valves
with
6.3V AC heaters and a voltage doubler and rectifier to provide the
"HT".
I recall a one valve design in Radio Constructor, which I build.
It
was
the 'cover article'. The design called for an Eddystone Box, far
too
expensive, so I used a tin box from some short bread.

I remember back in the 70's we had radar sets with ZERO volts on
the
magnetron's anode (DC ground). Of course, there was -3KV or so
on
the
cathode

I haven't done anything with radar in well over 30 years, so I
don't
know if they still do it or not. But I wouldn't be surprised.
At
first
glance it sounds crazy - but it made for a very simple and
efficient way
to couple the output of the magnetron to the waveguide.

No reason why it shouldn't be done. I can imagine some of the more
"technically challenged" struggling with it but there are always
those
who insist that all who have been designing kit for years have
got it
wrong.

Indeed it is rather similar to what was done with TV and monitor
CRTs,
to interface the screen with people's living rooms at an
appropriate
potential!

Hmmm, they must have done it differently over there. I've been
bitten
a number of times by not being careful around the anode lead on a
CRT.
The cathode is nearer ground potential because it's exposed on the
back of the tube.

You'd think being bitten by 25KV the first time would teach me a
lesson. But some people never learn

I was a 1960s TV engineer in the UK. 15kV or so on the CRT anode was
normal. The viewer was protected by a thick layer of glass that also
formed an implosion guard. Colour CRTs had around 25kV on the anode,
and
in early models with anode currents of 1mA or so the line output
stage
was lead shielded to reduce X-radiation. Happy days.

Yup, same here. Except when you jig the chassis up for testing, the
anode lead is basically hanging in the air. Also, the CRT makes a
great
capacitor - if you don't discharge it enough times before
disconnecting
the anode lead, it can still set you back on your backside

If you discharged it by simply shorting the anode to chassis you could
damage the CRT.

I've heard that, but it never happened to me or anyone I know. But I
also agree that doesn't mean it can't happen.

Dead shorts to ground tend to smoke things.

Not necessarily with static charges - which is what's on the CRT with the
HV removed.

Lightning is a static discharge, are you saying that doesn't smoke things?

The practical point is that the capacitance of a CRT is quite low,
limiting the amount of energy stored at a given potential. It's not a
negligible amount though. I suppose you could describe the charge on a
large power supply capacitor as a static charge too, but that is
definitely not negligible.

--

Percy Picacity

In article
,
Brian Reay wrote:

Percy Picacity wrote:


Not necessarily with static charges - which is what's on the CRT with the
HV removed.

Lightning is a static discharge, are you saying that doesn't smoke things?

The practical point is that the capacitance of a CRT is quite low,
limiting the amount of energy stored at a given potential. It's not a
negligible amount though. I suppose you could describe the charge on a
large power supply capacitor as a static charge too, but that is
definitely not negligible.


Energy stored in the cap is 0.5 CV^2

If V is large, as in a CRT, V^2 is going to be something to worry about.

On reflection, I agree. The capacitance of a CRT is about 10^7 lower
than of a PSU capacitor, but V^2 is about 10^7 higher - so about the
same energy.


That simple formula is the reason, in applications requiring a brief 'hold
up', PSUs in aircraft etc often have a voltage doubler on their input so
the can extend the hold up time by storing more energy for a given C.

(Adding a battery is not permitted by the aircraft design rules.)

--

Percy Picacity

On 2/21/2014 3:12 AM, FranK Turner-Smith G3VKI wrote:
"Jerry Stuckle" wrote in message
...
On 2/20/2014 4:15 PM, Brown Sugar wrote:
On 19/02/2014 18:51, Jerry Stuckle wrote:
On 2/19/2014 1:35 PM, Frank Turner-Smith G3VKI wrote:
On 19/02/14 03:09, Jerry Stuckle wrote:
On 2/18/2014 7:06 PM, FranK Turner-Smith G3VKI wrote:
"Jerry Stuckle" wrote in message
...
On 2/18/2014 4:29 PM, Percy Picacity wrote:
In article , Brian Reay
wrote:
On 18/02/14 20:31, Jerry Stuckle wrote:
There was a time, back inthe 1920s and 1930s, that any active
device
(valves in them thar days, tubes for the leftpondians) would
cost nearly
a week's wages for the average working man, and so it was
good
economical
sense to try and use it as many ways as possible
simultaneously.
Times have changes, and active devices with performance into
the
tens
of MegaHertz are now ten-a-penny, so what is achieved by
competitions
such as the "Two Transistor Challenge" where it is the
costs of
switching (manual, relays) which would be the major outlay?
Not carping, just curious.

There have always been "contests" like that, though sometimes
they were
about "build a whole receiver using the same transistor
type", or
"build a receiver without any ICs" after ICs had come around.

What I find intriguing is the realisation that valves
("tubes" to
you?) can be operated with only 12V on the anode.

No unusual at all.

Not only were a number of valves for the car radio (and possibly
other)
markets available, I recall designs which use 'ordinary' valves
with
6.3V AC heaters and a voltage doubler and rectifier to provide
the
"HT".
I recall a one valve design in Radio Constructor, which I
build. It
was
the 'cover article'. The design called for an Eddystone Box, far
too
expensive, so I used a tin box from some short bread.

I remember back in the 70's we had radar sets with ZERO volts on
the
magnetron's anode (DC ground). Of course, there was -3KV or
so on
the
cathode

I haven't done anything with radar in well over 30 years, so I
don't
know if they still do it or not. But I wouldn't be
surprised. At
first
glance it sounds crazy - but it made for a very simple and
efficient way
to couple the output of the magnetron to the waveguide.

No reason why it shouldn't be done. I can imagine some of the
more
"technically challenged" struggling with it but there are always
those
who insist that all who have been designing kit for years have
got it
wrong.

Indeed it is rather similar to what was done with TV and monitor
CRTs,
to interface the screen with people's living rooms at an
appropriate
potential!

Hmmm, they must have done it differently over there. I've been
bitten
a number of times by not being careful around the anode lead on a
CRT.
The cathode is nearer ground potential because it's exposed on the
back of the tube.

You'd think being bitten by 25KV the first time would teach me a
lesson. But some people never learn

I was a 1960s TV engineer in the UK. 15kV or so on the CRT anode was
normal. The viewer was protected by a thick layer of glass that also
formed an implosion guard. Colour CRTs had around 25kV on the anode,
and
in early models with anode currents of 1mA or so the line output
stage
was lead shielded to reduce X-radiation. Happy days.

Yup, same here. Except when you jig the chassis up for testing, the
anode lead is basically hanging in the air. Also, the CRT makes a
great
capacitor - if you don't discharge it enough times before
disconnecting
the anode lead, it can still set you back on your backside

If you discharged it by simply shorting the anode to chassis you could
damage the CRT.

I've heard that, but it never happened to me or anyone I know. But I
also agree that doesn't mean it can't happen.

Dead shorts to ground tend to smoke things.

Not necessarily with static charges - which is what's on the CRT with
the HV removed.

Lightning is a static discharge, are you saying that doesn't smoke things?

Now you're just trolling.


--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

On 21/02/2014 01:35, Jerry Stuckle wrote:
On 2/20/2014 4:15 PM, Brown Sugar wrote:
On 19/02/2014 18:51, Jerry Stuckle wrote:
On 2/19/2014 1:35 PM, Frank Turner-Smith G3VKI wrote:
On 19/02/14 03:09, Jerry Stuckle wrote:
On 2/18/2014 7:06 PM, FranK Turner-Smith G3VKI wrote:
"Jerry Stuckle" wrote in message
...
On 2/18/2014 4:29 PM, Percy Picacity wrote:
In article , Brian Reay
wrote:
On 18/02/14 20:31, Jerry Stuckle wrote:
There was a time, back inthe 1920s and 1930s, that any active
device
(valves in them thar days, tubes for the leftpondians) would
cost nearly
a week's wages for the average working man, and so it was good
economical
sense to try and use it as many ways as possible
simultaneously.
Times have changes, and active devices with performance into
the
tens
of MegaHertz are now ten-a-penny, so what is achieved by
competitions
such as the "Two Transistor Challenge" where it is the
costs of
switching (manual, relays) which would be the major outlay?
Not carping, just curious.

There have always been "contests" like that, though sometimes
they were
about "build a whole receiver using the same transistor
type", or
"build a receiver without any ICs" after ICs had come around.

What I find intriguing is the realisation that valves
("tubes" to
you?) can be operated with only 12V on the anode.

No unusual at all.

Not only were a number of valves for the car radio (and possibly
other)
markets available, I recall designs which use 'ordinary' valves
with
6.3V AC heaters and a voltage doubler and rectifier to provide the
"HT".
I recall a one valve design in Radio Constructor, which I
build. It
was
the 'cover article'. The design called for an Eddystone Box, far
too
expensive, so I used a tin box from some short bread.

I remember back in the 70's we had radar sets with ZERO volts on
the
magnetron's anode (DC ground). Of course, there was -3KV or
so on
the
cathode

I haven't done anything with radar in well over 30 years, so I
don't
know if they still do it or not. But I wouldn't be
surprised. At
first
glance it sounds crazy - but it made for a very simple and
efficient way
to couple the output of the magnetron to the waveguide.

No reason why it shouldn't be done. I can imagine some of the more
"technically challenged" struggling with it but there are always
those
who insist that all who have been designing kit for years have
got it
wrong.

Indeed it is rather similar to what was done with TV and monitor
CRTs,
to interface the screen with people's living rooms at an
appropriate
potential!

Hmmm, they must have done it differently over there. I've been
bitten
a number of times by not being careful around the anode lead on a
CRT.
The cathode is nearer ground potential because it's exposed on the
back of the tube.

You'd think being bitten by 25KV the first time would teach me a
lesson. But some people never learn

I was a 1960s TV engineer in the UK. 15kV or so on the CRT anode was
normal. The viewer was protected by a thick layer of glass that also
formed an implosion guard. Colour CRTs had around 25kV on the anode,
and
in early models with anode currents of 1mA or so the line output
stage
was lead shielded to reduce X-radiation. Happy days.

Yup, same here. Except when you jig the chassis up for testing, the
anode lead is basically hanging in the air. Also, the CRT makes a
great
capacitor - if you don't discharge it enough times before
disconnecting
the anode lead, it can still set you back on your backside

If you discharged it by simply shorting the anode to chassis you could
damage the CRT.


I've heard that, but it never happened to me or anyone I know. But I
also agree that doesn't mean it can't happen.

Dead shorts to ground tend to smoke things.



Not necessarily with static charges - which is what's on the CRT with
the HV removed.

good point

--
J

On 2/21/2014 4:54 PM, Brian Reay wrote:
Brown Sugar wrote:
On 21/02/2014 01:35, Jerry Stuckle wrote:
Not necessarily with static charges - which is what's on the CRT with
the HV removed.

good point


Really?

What matters is the energy stored.

There is enough stored on the CRT to kill or at least do serious harm.

Calling it static charge doesn't make it any safer. Static charge can kill,
it depends how quickly the charge is transferred (the current).


Which is the whole reason for discharging the CRT (multiple times)
before working on it.

Did you read the entire thread? Or just the one post?

rest of irrelevant information snipped).

--
==================
Remove the "x" from my email address
Jerry Stuckle

==================

On 2/21/2014 5:35 PM, Brian Reay wrote:
Jerry Stuckle wrote:
On 2/21/2014 4:54 PM, Brian Reay wrote:
Brown Sugar wrote:
On 21/02/2014 01:35, Jerry Stuckle wrote:
Not necessarily with static charges - which is what's on the CRT with
the HV removed.

good point


Really?

What matters is the energy stored.

There is enough stored on the CRT to kill or at least do serious harm.

Calling it static charge doesn't make it any safer. Static charge can kill,
it depends how quickly the charge is transferred (the current).


Which is the whole reason for discharging the CRT (multiple times) before working on it.

Did you read the entire thread? Or just the one post?

rest of irrelevant information snipped).


Why then had you mentioned 'static'?


If you would have read the entire thread, you would have understood.

I'm not in the habit of repeating myself for those too lazy to read.


--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

On 21/02/2014 21:54, Brian Reay wrote:
Brown Sugar wrote:
On 21/02/2014 01:35, Jerry Stuckle wrote:
Not necessarily with static charges - which is what's on the CRT with
the HV removed.

good point


Really?

What matters is the energy stored.

There is enough stored on the CRT to kill or at least do serious harm.

Calling it static charge doesn't make it any safer. Static charge can kill,
it depends how quickly the charge is transferred (the current).

That is determined, as basic circuit theory dictates, by the source
impedance.

A Van deGraff generator can generator perhaps 10's of thousands of volts.
Enough to generate huge sparks. When I was at school, it was common
practice for the teacher to have a ring of pupils touching it and have
sparks jumping between metal rods they held. They all lived to write it up.
It was safe because the source impedance was high (rate of energy transfer
low).

Had he tried it with 240V, he would be up on a murder charge. Low source
impedance, the mains can supply a lot of energy quickly.

good point


--
J

I remember a value of ~500pf for a 28" colour tube. It will of course, vary
according to the thickness of glass and surface area of coatings etc.

On 20/02/2014 15:08, gareth wrote:
"AndyW" wrote in message
...
On 20/02/2014 11:51, gareth wrote:
"AndyW" wrote in message
...
On 19/02/2014 09:32, gareth wrote:
LED or nitro-benzine as the polariser?
Polariser?
To my eternal regret, because I disposed of them 38 years ago, I had a
pile of "Amateur Wireless" from the 1930s within which were designs
for mirror-drum scanners, and the modulation was not by a neon light
but with a constant light source which was then modulated by a series
of polarising filters, with one being variable to rotate the
polarisation.
ISTR (38 years ago!!!) that the liquid used was nitro-benzene
OK I follow you now. I had a quick google and found out about nitrobenzene
and modulating polarisation. Never heard of it before. Live and learn.
My original set up was as simple and agricultural as they come, vinyl LP,
scrap motor from a cassette player, Neon attached to am amplifier behind
the 'screen' and a camera made from a lens and an LDR recording onto a
cassette player - the bandwidth was low enough to record on audio.
My latest televisor was made from a circle of black plastic spinning on a
hand fan with a very small torch behind it modulated by the sound from a
small mp3 player. It all folds up and fits in a pocket.


Wow! How many lines and frames / sec?

64 lines of low definition glory, I could not tell you of the frames per
second as I use the same TV as a camera by using the same disk, once the
frame starts are synced it works fine. The syncing is carried out by the
highly technical method of slowing the fan with an index finger.


Andy

"AndyW" wrote in message
...
On 20/02/2014 15:08, gareth wrote:
"AndyW" wrote in message
...
On 20/02/2014 11:51, gareth wrote:
"AndyW" wrote in message
...
On 19/02/2014 09:32, gareth wrote:
LED or nitro-benzine as the polariser?
Polariser?
To my eternal regret, because I disposed of them 38 years ago, I had a
pile of "Amateur Wireless" from the 1930s within which were designs
for mirror-drum scanners, and the modulation was not by a neon light
but with a constant light source which was then modulated by a series
of polarising filters, with one being variable to rotate the
polarisation.
ISTR (38 years ago!!!) that the liquid used was nitro-benzene
OK I follow you now. I had a quick google and found out about
nitrobenzene
and modulating polarisation. Never heard of it before. Live and learn.
My original set up was as simple and agricultural as they come, vinyl
LP,
scrap motor from a cassette player, Neon attached to am amplifier behind
the 'screen' and a camera made from a lens and an LDR recording onto a
cassette player - the bandwidth was low enough to record on audio.
My latest televisor was made from a circle of black plastic spinning on
a
hand fan with a very small torch behind it modulated by the sound from a
small mp3 player. It all folds up and fits in a pocket.


Wow! How many lines and frames / sec?

64 lines of low definition glory, I could not tell you of the frames per
second as I use the same TV as a camera by using the same disk, once the
frame starts are synced it works fine. The syncing is carried out by the
highly technical method of slowing the fan with an index finger.


Picking up on your BW comment, AIUI, the Baird transmssions of 30 line
pictures
were also of the audio BW, and were transmitted as part of the normal
broadcast,
but not at the same time as the audio; it was either speech or video, but
not
simultaneously!