"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.