In article ,
Ian Jackson wrote:
In message , "Dave Plowman (News)"
writes
In article ,
charles wrote:
My father said he once knew a man who lived near Crystal Palace and
claimed he could hear the radio all the time because of a poor metal
filling in a tooth.


but, in those days CP only broadcast tv!

And these days, only FM radio wise? Which would be less likely to produce
an audio output under those conditions.

Perhaps it was the old AM TV sound.

These days, Crystal Palace actually does transmit MW - 720kHz Radio 4
fill-in. It used to be at Lots Road power station
https://www.google.co.uk/?gws_rd=ssl...+power+station

Ah. I really can't remember the last time I used AM. I do have an AM
tuner, but it's switched off until needed, being valve. ;-)

--
*We have enough youth, how about a fountain of Smart?

Dave Plowman London SW
To e-mail, change noise into sound.

On Thu, 25 Feb 2016 16:14:31 +0000, pamela wrote:

On 15:03 25 Feb 2016, Graham. wrote:

====snip====

It would if you didn't LPF it first, which would be essential.

No, you are going to have to

LPF?

Low Pass Filter. In this case, the placement of a smoothing capacitor of
a few tens of microfarads (as opposed to a few nanoFarads usually used to
block only the rf ripple after the detector diode) - (modern stand-in for
the original lead galena crystal and cat's whisker used to build the very
first crystal sets) so that it smooths not only the rf ripple but the
audio frequency modulation as well - you're only interested in harvesting
a few milliwatts at best (unless you live right next door to the Tx in
question) of DC voltage produced by the detector diode that's rectifying
a conveniently strong signal to power a simple transistor amplified radio
receiver tuned to a wanted but weaker radio station.

If you're lucky enough to pick up a very strong 198Khz signal to power a
MW transistor receiver, it's job done. However, if you're relying on a
very strong MW signal to power your MW receiver, you'll have to get a bit
more inventive and use a second detector diode wired to give opposite
polarity with the usual rf ripple capacitor to allow the modulation to
get through, via a HPF, unmolested via a variable attenuator to the
detector of the transistor assisted reciever so as to null out the
unwanted audio that would otherwise swamp the weaker signals you're
trying to listen to. I have to admit though, this isn't something I've
ever tried. It's purely theoretical on my part (and it's just possible
there might be a flaw in this excellent theory of mine :-).

--
Johnny B Good

On Thursday, 25 February 2016 22:21:13 UTC, Andrew Gabriel wrote:
In article ,
"Dan S. MacAbre" writes:

Apologies to those who know about this stuff, if this is a stupid
question. Seeing the electronics thread reminded me of some of my
mis-spent youth. I never knew enough about electronics to design
anything, but I could usually get something like an amp or a tape
recorder from the tip, and fix it. That was about my limit. I used to
enjoy making crystal radios from some of the bits I'd have lying around,
but no matter what I used, I only ever seemed to be able to pick up what
seemed to be radio 4. If you were to build one nowadays, would there be
any suitable non-digital station left to pick up?

Funny you should mention this...
A couple of weeks ago, I stayed over at my parents, and in the bookshelf
was my old Ladybird book on making a radio, which takes you through the
stages of making the receiver and then adding an amplifier to it.
If you can still buy OC71's, it would still work today. ;-)

http://www.mds975.co.uk/Content/geor...trf_radio.html

Unusual method of biasing/driving the OC71.
Last time I looked you could still buy germaniums, albeit a very minimal range.


NT

Dave Plowman (News) wrote
Dan S. MacAbre wrote

You can have reasonable lighting run purely off RF.
If you are close enough to a powerful transmitter and
have a big enough aerial. Until they catch you, of course.

It's actually been made illegal, or something?

I'd guess it would be stealing energy or somesuch.

Guess again, legally, it isnt.

I'd have thought they would encourage you to do it.

Trouble is it removes or reduces the RF signal beyond that point.

Fantasy.

Story was a farmer or something used it to light a cow shed or whatever -
close to the BBC LW tramsmitter and caused a vast shadow in its output.
Many many years ago.

Don’t believe that vast claim.

I was wondering if you could just slowly
charge batteries off it. I never imagined you could run lighting off it.

To get any appreciable current, you'd need a very large
and efficient aerial and be close to the transmitter. Likely
cost far more than anything you could get for free.

On Friday, 26 February 2016 04:01:20 UTC, Rod Speed wrote:
Dave Plowman (News) wrote
Dan S. MacAbre wrote

You can have reasonable lighting run purely off RF.
If you are close enough to a powerful transmitter and
have a big enough aerial. Until they catch you, of course.

Trouble is it removes or reduces the RF signal beyond that point.

Fantasy.

If it doesn't you've just discovered a source of endless free energy. Twonk.

On 25/02/2016 11:34, Davey wrote:

My school had an old Scientific Encyclopedia which included instructions
for making a Morse Code-like Wireless transmitter. It used a spark gap
to generate the signal.
We didn't build one after all.


I built one, using the carbon rods out of two U2 batteries to produce an
arc. A lovely white light as I remember.

Bill

On 25/02/2016 10:30, Syd Rumpo wrote:

Wikipedia has a list of European (which we're still in) AM transmitters.

We're considering leaving the EEC, not Europe.

Bill

wrote in message
...
On Friday, 26 February 2016 04:01:20 UTC, Rod Speed wrote:
Dave Plowman (News) wrote
Dan S. MacAbre wrote

You can have reasonable lighting run purely off RF.
If you are close enough to a powerful transmitter and
have a big enough aerial. Until they catch you, of course.

Trouble is it removes or reduces the RF signal beyond that point.

Fantasy.

If it doesn't you've just discovered a source of endless free energy.

Even sillier and more pig ignorant than you usually manage on the removes.

Twonk.

Your sig is sposed to have a line with just -- on it in front of it,
gutless.

In article ,
Dave Plowman (News) wrote:
In article ,
Cursitor Doom wrote:
On Thu, 25 Feb 2016 10:08:37 +0000, Dan S. MacAbre wrote:

I only ever seemed to be able to pick up what
seemed to be radio 4.

I'm guessing that would have been the World Service. At 1MW DC input
power, it dominated the xtal radios of the small boys all over Britain.
Does this sound familiar:

https://www.youtube.com/watch?v=B4BZrSj2VU4

I don't think so. The world service being easily available at all times in
the UK is relatively recent.

The item shows refers to shortwave coverage. It used to be reasonably
accessible in the UK. When I joined EID, the car radios had a short wave
band and I did listen.

The most likely transmitter to receive (apart from a very local one) would
have been Droitwich LW. Which transmitted the Light Programme when I were
a lad. Later changed to R4 during the day, WS at night.

Droutwich carrying World Service is relatively new. Until Orfordness was
opened (late 70s?) the medium wave came from Crowborough (Aspidistra) which
used quite directional aerials, so not much UK coverage)

--
from KT24 in Surrey, England

In article ,
Bill Wright wrote:
On 25/02/2016 10:30, Syd Rumpo wrote:

Wikipedia has a list of European (which we're still in) AM transmitters.

We're considering leaving the EEC, not Europe.

Rubbish! we're going to cut the mooring ropes and row the islands across
the Atlantic.

--
from KT24 in Surrey, England

In article ,
Chris Hogg wrote:
On Thu, 25 Feb 2016 22:56:29 +0000 (GMT), charles
wrote:

In article ,
Chris Hogg wrote:
On Thu, 25 Feb 2016 22:21:00 GMT, pamela wrote:

On 16:52 25 Feb 2016, Chris Hogg wrote:

On Thu, 25 Feb 2016 16:14:31 GMT, pamela
wrote:


It says 1981 but I thought I had it before then.

"Electronics Simplified: Crystal Set Construction"
http://www.amazon.co.uk//dp/0859340678


'Radio for Boys', E.N. Bradley, 1956 edition, Junior Teach
Yourself Books. http://tinyurl.com/h7jgjdq Oddly enough, this
one says it was a school prize and has a label inside to that
effect. So was mine, and so has mine.

Covered crystal set, one- two- three- and four-valve TRF battery
receivers, battery and mains supehets. Still got the book! I
don't recall ever getting beyond the one-valve receiver,
although I have component costs for the others scribbled in
pencil in the margins, e.g. Mullard DL35 output valve 12/6,
Octal valve holder 6d etc. Those were the days!

Well done for getting as far as that one-valve receiver! Valves
are before my time.

This table says 12/6 in 1960 is equivalent to a bit more than £11 in
today's money. That seems too little.

http://swanlowpark.co.uk/rpiannual.jsp

Valves were almost all there were in those days. Transistors were only
just becoming available.

we "experimented" with transitors at school in 1957. I still have a copy
of the Mullard Book - Transistors for the Experimenter - published in
August 1956!

At about that time, I had a Henry's Radio 'Major' two-transistor radio
built from a kit, that I had at boarding-school. Red spot and white
spot transistors, http://tinyurl.com/zwcoxxv . In those days Henry's
Radio was a cramped little shop at the top end of Harrow Road, No 5.
Stuffed full of ex-WD equipment; you could hardly move in there. Then
the whole area was massively redeveloped,

The Edgeware Road flyover was the culprit.

and by 1964 they had moved into Edgeware Road, and look at them now!
Their ad from 1964 is on the back page of that issue of PW linked to
earlier.

They've left the area They're now in Edgeware itself.

--
from KT24 in Surrey, England

In message , charles
writes
In article ,
Dave Plowman (News) wrote:
In article ,
Cursitor Doom wrote:
On Thu, 25 Feb 2016 10:08:37 +0000, Dan S. MacAbre wrote:

I only ever seemed to be able to pick up what
seemed to be radio 4.

I'm guessing that would have been the World Service. At 1MW DC input
power, it dominated the xtal radios of the small boys all over Britain.
Does this sound familiar:

https://www.youtube.com/watch?v=B4BZrSj2VU4

I don't think so. The world service being easily available at all times in
the UK is relatively recent.

The item shows refers to shortwave coverage. It used to be reasonably
accessible in the UK. When I joined EID, the car radios had a short wave
band and I did listen.

The most likely transmitter to receive (apart from a very local one) would
have been Droitwich LW. Which transmitted the Light Programme when I were
a lad. Later changed to R4 during the day, WS at night.

Droutwich carrying World Service is relatively new. Until Orfordness was
opened (late 70s?) the medium wave came from Crowborough (Aspidistra) which
used quite directional aerials, so not much UK coverage)

IIRC, overnight, Droitwich has been carrying the BBC's Overseas Service
/ World Service for a long, long time - long before they stopped the MW
transmissions.

--
Ian

On 26/02/2016 05:58, Bill Wright wrote:
On 25/02/2016 10:30, Syd Rumpo wrote:

Wikipedia has a list of European (which we're still in) AM transmitters.

We're considering leaving the EEC, not Europe.

Bill

The EEC hasn't existed since 1993.

But I know what you mean, and you knew what I meant.

Cheers
--
Syd

Andrew Gabriel wrote:
In article ,
"Dan S. MacAbre" writes:
Apologies to those who know about this stuff, if this is a stupid
question. Seeing the electronics thread reminded me of some of my
mis-spent youth. I never knew enough about electronics to design
anything, but I could usually get something like an amp or a tape
recorder from the tip, and fix it. That was about my limit. I used to
enjoy making crystal radios from some of the bits I'd have lying around,
but no matter what I used, I only ever seemed to be able to pick up what
seemed to be radio 4. If you were to build one nowadays, would there be
any suitable non-digital station left to pick up?

Funny you should mention this...
A couple of weeks ago, I stayed over at my parents, and in the bookshelf
was my old Ladybird book on making a radio, which takes you through the
stages of making the receiver and then adding an amplifier to it.
If you can still buy OC71's, it would still work today. ;-)

http://www.mds975.co.uk/Content/geor...trf_radio.html


I have the Ladybird book, too. The illustrations are just beautiful.
Without that, I'm not sure that I would even have tried to make one.
For years after, everything I made was built on a piece of board with
brass screws, just like the Ladybird radio. It added an amusing and
personal touch to everything.

Bill Wright wrote:
On 25/02/2016 11:34, Davey wrote:

My school had an old Scientific Encyclopedia which included instructions
for making a Morse Code-like Wireless transmitter. It used a spark gap
to generate the signal.
We didn't build one after all.


I built one, using the carbon rods out of two U2 batteries to produce an
arc. A lovely white light as I remember.

Bill

I remember digging some of those out to do chemistry experiments at
home. And doing electrolysis with the filament stalks of a broken and
smashed light bulb.

On 26/02/16 03:01, wrote:
On Thursday, 25 February 2016 22:21:13 UTC, Andrew Gabriel wrote:
In article ,
"Dan S. MacAbre" writes:

Apologies to those who know about this stuff, if this is a stupid
question. Seeing the electronics thread reminded me of some of my
mis-spent youth. I never knew enough about electronics to design
anything, but I could usually get something like an amp or a tape
recorder from the tip, and fix it. That was about my limit. I used to
enjoy making crystal radios from some of the bits I'd have lying around,
but no matter what I used, I only ever seemed to be able to pick up what
seemed to be radio 4. If you were to build one nowadays, would there be
any suitable non-digital station left to pick up?

Funny you should mention this...
A couple of weeks ago, I stayed over at my parents, and in the bookshelf
was my old Ladybird book on making a radio, which takes you through the
stages of making the receiver and then adding an amplifier to it.
If you can still buy OC71's, it would still work today. ;-)

http://www.mds975.co.uk/Content/geor...trf_radio.html

Unusual method of biasing/driving the OC71.
Indeed. The first transistor radio I built was a 27Mhz RC radio and it
was biased like that. It worked. Until I left in on a window sill in the
sun. I then discovered things like 'temperature stability'...


Last time I looked you could still buy germaniums, albeit a very minimal range.


lots of dealers in old new stock as it were. Same as valves.


NT



--
New Socialism consists essentially in being seen to have your heart in
the right place whilst your head is in the clouds and your hand is in
someone else's pocket.

On 26/02/16 09:07, charles wrote:
In article ,
Bill Wright wrote:
On 25/02/2016 10:30, Syd Rumpo wrote:

Wikipedia has a list of European (which we're still in) AM transmitters.

We're considering leaving the EEC, not Europe.

Rubbish! we're going to cut the mooring ropes and row the islands across
the Atlantic.

And park it somewhere in the Caribbean, as a tax haven.

Have to saw Scotland off first though, or we will sink....


--
A lie can travel halfway around the world while the truth is putting on
its shoes.

The Natural Philosopher wrote:
On 26/02/16 09:07, charles wrote:
In article ,
Bill Wright wrote:
On 25/02/2016 10:30, Syd Rumpo wrote:

Wikipedia has a list of European (which we're still in) AM transmitters.

We're considering leaving the EEC, not Europe.

Rubbish! we're going to cut the mooring ropes and row the islands across
the Atlantic.

And park it somewhere in the Caribbean, as a tax haven.

Have to saw Scotland off first though, or we will sink....



Unlikely. Scotland is still bobbing up after the last ice age. ;-)

Tim

Tim+ wrote:
The Natural Philosopher wrote:
On 26/02/16 09:07, charles wrote:
In article ,
Bill Wright wrote:
On 25/02/2016 10:30, Syd Rumpo wrote:

Wikipedia has a list of European (which we're still in) AM transmitters.

We're considering leaving the EEC, not Europe.

Rubbish! we're going to cut the mooring ropes and row the islands across
the Atlantic.

And park it somewhere in the Caribbean, as a tax haven.

Have to saw Scotland off first though, or we will sink....



Unlikely. Scotland is still bobbing up after the last ice age. ;-)

Tim


And the south is bobbing down in response, apparently.

In article ,
charles wrote:
I'm guessing that would have been the World Service. At 1MW DC input
power, it dominated the xtal radios of the small boys all over
Britain. Does this sound familiar:

https://www.youtube.com/watch?v=B4BZrSj2VU4

I don't think so. The world service being easily available at all
times in the UK is relatively recent.

The item shows refers to shortwave coverage. It used to be reasonably
accessible in the UK.

Yes - but on a crystal set? They may have existed, but I don't ever
remember seeing one for SW.

--
*If God dropped acid, would he see people?

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
The Natural Philosopher wrote:
Rubbish! we're going to cut the mooring ropes and row the islands
across the Atlantic.

And park it somewhere in the Caribbean, as a tax haven.

Surrounded by blacks? Have you run this by your kipper pals?

--
*Toilet stolen from police station. Cops have nothing to go on.

Dave Plowman London SW
To e-mail, change noise into sound.

On Fri, 26 Feb 2016 09:10:38 +0000, charles wrote:

They've left the area They're now in Edgeware itself.

Tottenham Court Road used to be the mecca for electronic hobbyists back
in the day. They stocked *real* stuff back then; today it's just a load
of brand new consumer tech gadgets.

On Fri, 26 Feb 2016 09:05:45 +0000, charles wrote:

Droutwich carrying World Service is relatively new. Until Orfordness was
opened (late 70s?) the medium wave came from Crowborough (Aspidistra)
which used quite directional aerials, so not much UK coverage)

They weren't as directional as they originally thought - and hoped. They
only found out about 30 years later that the gain in desired direction
was pretty much zero. I enjoyed a guided tour around it when it was still
operational; mostly underground and like something out of James Bond.

On Fri, 26 Feb 2016 00:12:41 +0000, The Natural Philosopher wrote:

You can still buy oc71s all right

But why not use something better?

Can you name a better photo-transistor than the OC71?
;-)

On 26/02/16 11:33, Cursitor Doom wrote:
On Fri, 26 Feb 2016 09:10:38 +0000, charles wrote:

They've left the area They're now in Edgeware itself.

Tottenham Court Road used to be the mecca for electronic hobbyists back
in the day. They stocked *real* stuff back then; today it's just a load
of brand new consumer tech gadgets.


Those are nearly gone as well. It's now coffee bars, restaurants, sports
wear and furniture shops.

--
Adrian C

In message , Tim+
writes
The Natural Philosopher wrote:

Have to saw Scotland off first though, or we will sink....

Unlikely. Scotland is still bobbing up after the last ice age. ;-)

Yah ********. Get digging - only 50 miles from Stirling to Dumbarton.
You can have the bits below that line, including Nicola :-)
--
Graeme

In article , The Natural Philosopher
scribeth thus
On 25/02/16 14:14, Dan S. MacAbre wrote:
Dave Plowman (News) wrote:
In article ,
Dan S. MacAbre wrote:
Only exception, if it's needed at all, are those parasitic
circuits which used two tuners. One to draw radio energy from a
powerful station used to improve reception of the station you
listen to.


I'd never heard of that. I wonder how much power could be obtained from
such a thing?

You can have reasonable lighting run purely off RF. If you are close
enough to a powerful transmitter and have a big enough aerial. Until they
catch you, of course.

It's actually been made illegal, or something? I'd have thought they
would encourage you to do it. I was wondering if you could just slowly
charge batteries off it. I never imagined you could run lighting off it.

Well average TV transmitter is around 100-250KW and you get 4+ up a
standard mast.

Rarely these days much more that about a 100K for a main station, the
olde analogue was peak sync power the average was a lot lower then that
it appeared to be.

But it is in a Very tight beam towards the distant horizon it costs too
much money to generate and waste heating up the ground locally!..


Think broadcast AM is broadly similar.

Which mat be why in the end BBC3 is moving online. It could be that it
costs less for the number of actual viewers.




A standard fluorescent tube will light with no other connections close to
some TX aerials.





--
Tony Sayer

IIRC it picked up the Light programme from Droitwich (100 miles)
and the Home service from Moorside Edge (30 miles)

basically a coil and tuning capacitor like from an old tranny radio.,
plus a oa91 germanium diode and a crystal earpiece should all still work.

Certainly, high impedance headphones were necessary. Ex-WD ones were
easily available in the early 1950's, wire-wound, several kilohms,
with steel diaphragms. A good earth was also important.


In fact I'm involved in a community radio station and recently we did a
thing with some local schools re radio and what it was all about. Part of
that was we made up some crystal set kits which the children put
together. They were amazed that they worked and all ran off home with
them proudly boasting that they could make a radio!.

Only problem is that AM transmitters are starting to be shut down now:-(
--
Tony Sayer

On Fri, 26 Feb 2016 11:52:33 +0000, pamela wrote:

Why would a MW "power" station have to be treated differently to 198lHz
in the way you describe in your second paragraph (which I can't say I
fully understand)?

I think the answer to that is in the 3rd paragraph.

On 26/02/16 11:40, Cursitor Doom wrote:
On Fri, 26 Feb 2016 00:12:41 +0000, The Natural Philosopher wrote:

You can still buy oc71s all right

But why not use something better?

Can you name a better photo-transistor than the OC71?
;-)

OCP71?


--
Karl Marx said religion is the opium of the people.
But Marxism is the crack cocaine.

On 26/02/16 10:45, Tim+ wrote:
The Natural Philosopher wrote:
On 26/02/16 09:07, charles wrote:
In article ,
Bill Wright wrote:
On 25/02/2016 10:30, Syd Rumpo wrote:

Wikipedia has a list of European (which we're still in) AM transmitters.

We're considering leaving the EEC, not Europe.

Rubbish! we're going to cut the mooring ropes and row the islands across
the Atlantic.

And park it somewhere in the Caribbean, as a tax haven.

Have to saw Scotland off first though, or we will sink....



Unlikely. Scotland is still bobbing up after the last ice age. ;-)


It was till the SNP took over.

Tim



--
Karl Marx said religion is the opium of the people.
But Marxism is the crack cocaine.

On Fri, 26 Feb 2016 14:27:50 +0000, Chris Hogg wrote:

On Fri, 26 Feb 2016 14:15:26 +0000, The Natural Philosopher
wrote:

On 26/02/16 11:40, Cursitor Doom wrote:
On Fri, 26 Feb 2016 00:12:41 +0000, The Natural Philosopher wrote:

You can still buy oc71s all right

But why not use something better?

Can you name a better photo-transistor than the OC71?
;-)

OCP71?

IIRC if you carefully stripped the paint off an OC71 you had an OCP71.

Exactly. Well remembered.

On Friday, 26 February 2016 11:36:16 UTC, Cursitor Doom wrote:
On Fri, 26 Feb 2016 09:10:38 +0000, charles wrote:

They've left the area They're now in Edgeware itself.

Tottenham Court Road used to be the mecca for electronic hobbyists back
in the day. They stocked *real* stuff back then; today it's just a load
of brand new consumer tech gadgets.

Last time I went down there the red light stuff had taken over I used to like Proops etc.


NT

On 26/02/2016 15:19, Cursitor Doom wrote:
On Fri, 26 Feb 2016 14:27:50 +0000, Chris Hogg wrote:

On Fri, 26 Feb 2016 14:15:26 +0000, The Natural Philosopher
wrote:

On 26/02/16 11:40, Cursitor Doom wrote:
On Fri, 26 Feb 2016 00:12:41 +0000, The Natural Philosopher wrote:

You can still buy oc71s all right

But why not use something better?

Can you name a better photo-transistor than the OC71?
;-)

OCP71?

IIRC if you carefully stripped the paint off an OC71 you had an OCP71.

Exactly. Well remembered.

Until they started filling them with opaque blue gel, same as was used
for some if not all OC44s etc.

Cheers
--
Syd

On Friday, 26 February 2016 09:55:38 UTC, The Natural Philosopher wrote:
On 26/02/16 03:01, tabbypurr wrote:
On Thursday, 25 February 2016 22:21:13 UTC, Andrew Gabriel wrote:
In article ,
"Dan S. MacAbre" writes:

Apologies to those who know about this stuff, if this is a stupid
question. Seeing the electronics thread reminded me of some of my
mis-spent youth. I never knew enough about electronics to design
anything, but I could usually get something like an amp or a tape
recorder from the tip, and fix it. That was about my limit. I used to
enjoy making crystal radios from some of the bits I'd have lying around,
but no matter what I used, I only ever seemed to be able to pick up what
seemed to be radio 4. If you were to build one nowadays, would there be
any suitable non-digital station left to pick up?

Funny you should mention this...
A couple of weeks ago, I stayed over at my parents, and in the bookshelf
was my old Ladybird book on making a radio, which takes you through the
stages of making the receiver and then adding an amplifier to it.
If you can still buy OC71's, it would still work today. ;-)

http://www.mds975.co.uk/Content/geor...trf_radio.html

Unusual method of biasing/driving the OC71.
Indeed. The first transistor radio I built was a 27Mhz RC radio and it
was biased like that. It worked. Until I left in on a window sill in the
sun. I then discovered things like 'temperature stability'...


Last time I looked you could still buy germaniums, albeit a very minimal range.


lots of dealers in old new stock as it were. Same as valves.

Last time I looked I found new ones at Rapid. That was over a decade ago though. Not sure what anyone does with them any more.


NT

In message ,
writes

Last time I looked I found new ones at Rapid. That was over a decade
ago though. Not sure what anyone does with them any more.

OC71s still available via eBay. Well, they would be, I suppose.
--
Graeme

In article ,
wrote:
Last time I looked you could still buy germaniums, albeit a very
minimal range.


lots of dealers in old new stock as it were. Same as valves.

Last time I looked I found new ones at Rapid. That was over a decade ago
though. Not sure what anyone does with them any more.

PNP can be useful, though.

--
*They call it PMS because Mad Cow Disease was already taken.

Dave Plowman London SW
To e-mail, change noise into sound.

In article , says...


I did wonder if nearby you could receive the long wave transmissions -
198kHz @ 500kW - with just wire, a diode and a loudspeaker.


More years ago than I care to remember I heard a report on the radio about a
woman living close to the Droitwich transmitter who could receive the Light
Programme (in the days when it was on Long Wave) on her electric cooker ...

--

Terry

On Fri, 26 Feb 2016 11:52:33 +0000, pamela wrote:

On 02:08 26 Feb 2016, Johnny B Good wrote:

On Thu, 25 Feb 2016 16:14:31 +0000, pamela wrote:

On 15:03 25 Feb 2016, Graham. wrote:

====snip====

It would if you didn't LPF it first, which would be essential.

No, you are going to have to

LPF?

Low Pass Filter. In this case, the placement of a smoothing capacitor
of a few tens of microfarads (as opposed to a few nanoFarads usually
used to block only the rf ripple after the detector diode) - (modern
stand-in for the original lead galena crystal and cat's whisker used to
build the very first crystal sets) so that it smooths not only the rf
ripple but the audio frequency modulation as well - you're only
interested in harvesting a few milliwatts at best (unless you live
right next door to the Tx in question) of DC voltage produced by the
detector diode that's rectifying a conveniently strong signal to power
a simple transistor amplified radio receiver tuned to a wanted but
weaker radio station.

If you're lucky enough to pick up a very strong 198Khz signal to power
a MW transistor receiver, it's job done. However, if you're relying on
a very strong MW signal to power your MW receiver, you'll have to get a
bit more inventive and use a second detector diode wired to give
opposite polarity with the usual rf ripple capacitor to allow the
modulation to get through, via a HPF, unmolested via a variable
attenuator to the detector of the transistor assisted reciever so as to
null out the unwanted audio that would otherwise swamp the weaker
signals you're trying to listen to. I have to admit though, this isn't
something I've ever tried. It's purely theoretical on my part

(and it's just possible there might be a flaw in this excellent theory
of mine :-).

Why would a MW "power" station have to be treated differently to 198lHz
in the way you describe in your second paragraph (which I can't say I
fully understand)?

Lack of selectivity in the MW tuning filter. A suitably strong enough MW
broadcast is likely to be heard "Right across the dial".

--
Johnny B Good

On Fri, 26 Feb 2016 14:00:31 +0000, Cursitor Doom wrote:

On Fri, 26 Feb 2016 11:52:33 +0000, pamela wrote:

Why would a MW "power" station have to be treated differently to 198lHz
in the way you describe in your second paragraph (which I can't say I
fully understand)?

I think the answer to that is in the 3rd paragraph.

Is that "third paragraph" a reference to the one I've just sent to
Pamela in reply to her question? :-)


--
Johnny B Good