Radio and Telegraph Accessories
Before Vacuum Tubes
Click on photo for larger picture.
This is a Marconi Transformer. The Copper Strap is all
one piece and the turns on the inner coil count up to
It is my guess that this is one of the first
transformers used to inductively couple a spark gap transmitter
to an antenna. Early on in the world of transmitting
Marconi's spark gap transmitter oscillator circuits
were all directly coupled to the antenna and ground.
This caused significant losses.
Ferdinand Braun developed the inductively
coupled transmitter (the antenna and ground circuit
being separated from the spark gap circuit) in his
early experiments with transmission in water. This led
to later experiments in free air transmission which
were quite successful.
Please e-mail me if you have further information.
Rhumkorff Induction Coil
This coil, often used in spark gap transmitters and other
equipment requiring high voltage, is similar in function
to a car's ignition coil. It has a set of "points" that,
instead of being opened and closed by the operation of a
cam, are opened and closed by the coil itself (an iron bar
inside of the coil acts as a magnetic "cam"). When the
coil has powered up (12 Volts works fine) the following
chain of events occur:
This coil seems to run between 40 and 80 Hertz
I am re researching the above operational
description as I am not satisfied of it's accuracy.
- The capacitor in the wooden base charges.
- The coil "charges", that is to say it's magnetic
- The "points" open (pulled open by the iron bar in
the center of the coil) cutting off power to the
capacitor and coil.
- The magnetic field starts to collapse the capacitor
releases it's energy in an attempt to sustain the
- The capacitor drains and the voltage induced in the
coil by the collapsing magnetic field rises until
sufficient to arc across the gap set by the arms
mounted above the coil.
- As the energy drains the points close again starting
the cycle over.
Acid battery called a Grenet Jar
A Philips "B" Battery Eliminator 1926 to 1929