The King's Microphone
 

On Feb 28, 6:20*pm, mikeos wrote:
On 28/02/2011 00:06, Martin Jay wrote: http://www.bbc.co.uk/news/uk-12591587:

* Can a 74-year-old microphone last spoken into by King George VI still

be used to broadcast live to the nation? Paddy O'Connell, presenter of
Radio 4's Broadcasting House, thought it might be worth a try.

The answer to the question is

No, it doesn't have a USB interface! :-)

The King's Microphone
 

" wrote in message
...
On Feb 28, 6:20 pm, mikeos wrote:
On 28/02/2011 00:06, Martin Jay wrote: http://www.bbc.co.uk/news/uk-12591587:

Can a 74-year-old microphone last spoken into by King George VI still

be used to broadcast live to the nation? Paddy O'Connell, presenter of
Radio 4's Broadcasting House, thought it might be worth a try.

The answer to the question is

No, it doesn't have a USB interface! :-)

When I was little, I dismantled an old carbon microphone to see how it worked
I just hope to God it wasn't the last surviving example of this.
http://www.btinternet.com/~roger.bec...h/mics/bth.htm

Only joking, but it was similar, suspended in a metal hoop on four springs.
it had a Bakelite base housing the "induction coil" transformer, I remember
being surprised that the core was made up of many parallel iron wires.

Needless to say, I wish I still had it.


--
Graham.

%Profound_observation%

The King's Microphone
 

Graham. wrote:

Only joking, but it was similar, suspended in a metal hoop on four springs.
it had a Bakelite base housing the "induction coil" transformer, I remember
being surprised that the core was made up of many parallel iron wires.

As a child I discovered that the carbon mike inserts used by the GPO
would get very hot if subject to a high voltage. This was during
attempts to get a usable audio link between our house and my mate's
using very thin blasting wire nicked from the quarry and a lot of
enormous batteries nicked from the railway.

Bill

The King's Microphone
 

"Bill Wright" wrote in message
...
Graham. wrote:

Only joking, but it was similar, suspended in a metal hoop on four
springs.
it had a Bakelite base housing the "induction coil" transformer, I
remember
being surprised that the core was made up of many parallel iron wires.

As a child I discovered that the carbon mike inserts used by the GPO would
get very hot if subject to a high voltage. This was during attempts to get
a usable audio link between our house and my mate's using very thin
blasting wire nicked from the quarry and a lot of enormous batteries
nicked from the railway.


I had a carbon hand mic in a very substatial bakelite case
and padding with a switch on the side. It had the British WD
mark and broad arrrow on the back plus RTC (Royal Tank Corps)
and 2DG (2nd Dragoon Guards) After a while, I exchanged it for a
78rpm record; "All Shook Up" which I still have. I wonder if that
spotty kid in short trousers still has my mic? I would like it back:-)


Iain

The King's Microphone
 

"Iain Churches" wrote in message
...

"Bill Wright" wrote in message
...
Graham. wrote:

Only joking, but it was similar, suspended in a metal hoop on four
springs.
it had a Bakelite base housing the "induction coil" transformer, I
remember
being surprised that the core was made up of many parallel iron wires.

As a child I discovered that the carbon mike inserts used by the GPO
would get very hot if subject to a high voltage. This was during attempts
to get a usable audio link between our house and my mate's using very
thin blasting wire nicked from the quarry and a lot of enormous batteries
nicked from the railway.


I had a carbon hand mic in a very substatial bakelite case
and padding with a switch on the side. It had the British WD
mark and broad arrrow on the back plus RTC (Royal Tank Corps)
and 2DG (2nd Dragoon Guards) After a while, I exchanged it for a
78rpm record; "All Shook Up" which I still have. I wonder if that
spotty kid in short trousers still has my mic? I would like it back:-)


I also had a microphone answering to more or less that description. Inside
was a standard "transmitter insert No 13", the carbon microphone used in GPO
telephones at the time. The "No 13" had an amazingly long service life,
introduced with the telephone 162 in the early 1930s it was used for all the
200 and 300 series telephones and early issues of the 700 series, finally
being replaced by the "transmitter insert No 21" in the mid 1960s. And then
the "21" was found to be far less reliable than the "13" had been. My first
job after leaving school was to test a huge batch of "21"s that he been
returned as "faulty", as part of a project to find out the cause of the
premature failure of the 21.

It was a different world back then.


David.

The King's Microphone
 

"David Looser" wrote in message
...
"Iain Churches" wrote in message
...

"Bill Wright" wrote in message
...
Graham. wrote:

Only joking, but it was similar, suspended in a metal hoop on four
springs.
it had a Bakelite base housing the "induction coil" transformer, I
remember
being surprised that the core was made up of many parallel iron wires.

As a child I discovered that the carbon mike inserts used by the GPO
would get very hot if subject to a high voltage. This was during
attempts to get a usable audio link between our house and my mate's
using very thin blasting wire nicked from the quarry and a lot of
enormous batteries nicked from the railway.


I had a carbon hand mic in a very substatial bakelite case
and padding with a switch on the side. It had the British WD
mark and broad arrrow on the back plus RTC (Royal Tank Corps)
and 2DG (2nd Dragoon Guards) After a while, I exchanged it for a
78rpm record; "All Shook Up" which I still have. I wonder if that
spotty kid in short trousers still has my mic? I would like it back:-)


I also had a microphone answering to more or less that description. Inside
was a standard "transmitter insert No 13", the carbon microphone used in
GPO telephones at the time. The "No 13" had an amazingly long service
life, introduced with the telephone 162 in the early 1930s it was used for
all the 200 and 300 series telephones and early issues of the 700 series,
finally being replaced by the "transmitter insert No 21" in the mid
1960s. And then the "21" was found to be far less reliable than the "13"
had been. My first job after leaving school was to test a huge batch of
"21"s that he been returned as "faulty", as part of a project to find out
the cause of the premature failure of the 21.

It was a different world back then.

:-)

Indeed. The mic looked a bit like a thick lollipop.
The top part of the body which contained the mic was
disc shaped about 7.5cm in diameter, and 3cms in depth.
The front was pierced with holes, and could be unscrewed,
and the insert removed. There was a spring loaded push
switch on the right hand side of the handle.

Did you find out why the type 21 failed?

Iain

The King's Microphone
 

"Iain Churches" wrote

Did you find out why the type 21 failed?


Yes, whilst the 13 had used solid carbon electrodes, the 21 used
"carbonised" steel electrodes. Due to surface contamination on the metal
prior to carbonisation there was not always a satisfactory bond at the
molecular level between the steel and the carbon, this allowed the surface
of the steel to corrode under the carbon layer. The solution was to improve
the cleaning of the surface of the steel prior to carbonisation.

Interestingly there was, even in the 1960s by which time when carbon
microphones had been in common use for some 80 years, no really satisfactory
theory of how they worked. The common theory at the time was that the
contact area between adjacent granules increased with increasing pressure,
but this could not explain why the *average* resistance increased with
increasing sound level. The theory that the group I was working in arrived
at was that the granules bounced off each other whilst activated by sound,
so that each point of contact became a sort of pulse-width modulator.

David.

The King's Microphone
 

"David Looser" wrote in message
...
"Iain Churches" wrote

Did you find out why the type 21 failed?


Yes, whilst the 13 had used solid carbon electrodes, the 21 used
"carbonised" steel electrodes. Due to surface contamination on the metal
prior to carbonisation there was not always a satisfactory bond at the
molecular level between the steel and the carbon, this allowed the surface
of the steel to corrode under the carbon layer. The solution was to
improve
the cleaning of the surface of the steel prior to carbonisation.

So does that mean that simpler was better, i.e more reliable?

Interestingly there was, even in the 1960s by which time when carbon
microphones had been in common use for some 80 years, no really
satisfactory
theory of how they worked. The common theory at the time was that the
contact area between adjacent granules increased with increasing pressure,

Carbon mics were not used in recording, but they were
described briefly in text books. The explanation you
write above is the one I remember reading.

Funny how I had almost forgotten about that old mic, and
all the fun we had with it (simple pleasures back in those
days:-) On Thursday evening my Dad and I used to sit
at the kitchen table and "make something, sometimes
it was a model ship, or plane, sometimes an amp or a
simple one valve radio. This mic was used with a one-valve
mic that had an anode cap - (pretty dangerous thing for
a pre-teen to be using), and a Rola speaker salvaged
from a "radio-gram" The amp was built in an Oxo tin chassis!
Later, the boy next door and I rigged a wire from the ground
terminal to a pole in the garden and fooled the other boys
into thinking it was a transmitter:-)


Shortly after that they packed me off to boarding school:-)
I joined the radio club and they taught me how to charge
up electrolytics. We we used to roll them under the beds
for the dorm-maids to find:-)

Iain

The King's Microphone
 

"Iain Churches" wrote in message
...
Funny how I had almost forgotten about that old mic, and
all the fun we had with it (simple pleasures back in those
days:-) On Thursday evening my Dad and I used to sit
at the kitchen table and "make something", sometimes
it was a model ship, or plane, sometimes an amp or a
simple one valve radio. This mic was used with a one-valve
mic that had an anode cap - (pretty dangerous thing for
a pre-teen to be using), and a Rola speaker salvaged
from a "radio-gram" The amp was built in an Oxo tin chassis!
Later, the boy next door and I rigged a wire from the ground
terminal to a pole in the garden and fooled the other boys
into thinking it was a transmitter:-)


Shortly after that they packed me off to boarding school:-)
I joined the radio club and they taught me how to charge
up electrolytics. We we used to roll them under the beds
for the dorm-maids to find:-)

Iain
Sorry. Typo:(

Should read, "This mic was used with a one-valve
amplifier that had an anode cap.

The King's Microphone
 

In article ,
Iain Churches wrote:
Carbon mics were not used in recording, but they were
described briefly in text books. The explanation you
write above is the one I remember reading.

I'll bet they were in the early days. The BBC certainly used them for a
while.

--
*The modem is the message *

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