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

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