Aircraft Transmitter HT Transformer
This ancient wooden cased
item is a transformer used in a WW1 transmitter, much like the
one pictured above where you can see a similar transformer embedded
in the outer box. Because a transformer needs to work on AC not
DC, a springy steel strip is arranged to vibrate (like a buzzer).
Battery current to the transformer's primary coil passes through
a springy steel strip and iron-cored solenoid which pulls the
springy strip so it no longer carries any current. The natural
springiness of the strip then allows it to make contact again,
thus allowing current to flow whereupon the whole cycle repeats.
In this way an AC voltage is produced across the primary coil
which is magnetically coupled to the secondary coil which carries
a lot more turns of copper wire. A 6 volt battery can then produce
several hundred volts of rough AC which is used to power the
transmitter. In the example below the springy strip and the near
contact are missing, however... hidden away in a tiny latched
box in the unit above, I found a complete set of spares which
would I could use to fix this example. see
I notice this version of the
power supply has a hole under the free end of the spring steel
strip. This was originally fitted with a second adjuster which,
when combined with the main adjuster, could set the frequency
of operation. This frequency, which may have been maybe several
hundred cycles per second could be used to identify the particular
transmitter. Most WW1 transmitters were of course spark transmitters
and had a very broad output frequency and, if the waveband in
use had a lot of transmissions, one could identify these from
the pitch of their morse code. It seems aircraft transmissions
used a higher frequency spark than trench transmitters to identify
them as such.
Below you can see the end of
the (rusty) iron core used for attracting the springy steel strip. The hole orinally carried a screw on which there
were a combination of metal and rubber washers used for altering
the natural resonant frequency of the spring steel strip (also
missing). The inventor, Mortimer Arthur Codd was a motor engineer,
born in 1880, who in 1911 was running a small business employing
20 men making parts for the electrical system of motor cars.
During WW1 he branched out and was interested in power supplies
for spark transmitters, hence the 1915 patent mentioned below
the next picture. I looked for this chap in the 1911 census and
found something of passing interest. He was included twice..
once by himself at 15 Dryden Chambers, Oxford Street (presumably
his factory) and then by his father who registered his son at
his own address of 20 Palace Road, Streatham. His father was
clearly slightly unusual as he complained on the census form
about having to question his deaf maid as to her birth details
and was he fibbing about the exact whereabouts of his son? Dryden
Chambers used to be an arcade at 119 Oxford Street, filmed in
Hitchcock's film "Frenzy", but it's now built over
by shops and the alleyway no longer exists. Is that perhaps where
this little box was made?
Below, I've turned
the picture so you can read the numbers. I eventually discovered
that the patent number was GB191514382 which was revealed to
be a method of producing a higher than usual spark transmitter
tone for use by aircraft.
see the patent which was taken out by Mortimer Arthur Codd.