This is a Marconi Model
730 TRF Receiver
This TRF receiver,
designed in the early 1930s was used in ships until superseded
by more modern superhets.
Like a handful of manufacturers,
Marconi decided to use plug-in coils rather than a complex switching
arrangement. A few Eddystone and National HRO receivers had similar
It uses four old battery-powered
7-Pin British valves, type W21 pentodes popular during the mid
to late 30s before widespread use of octal types. One is missing.
There's also a 6-pin socket that's missing something. Looking
at the circuit at the bottom of this page, I think this was a
preset circuit tuned to the old international distress frequency
of 500Kc/s or 600 metres and selected by the mode switch on the
front panel when in the "STAND BI" position.
Arrayed along the top and under
the hinged top section is its set of plug-in coils. There are
10-wavebands, Range 8 coils are in place on the chassis, but
maybe the Range 4 set was surplus to requirements or just got
The set is built into a wooden case
fitted to rubber shock mounts. As can be seen below the top section,
holding the spare plug-in coils, hinges upwards for access to
extra coils and maintenance.
I'll take a better photo
soon. This shows an early crystal detector, above the Reaction
In an emergency situation
the receiver could be pressed into use as a crystal set.
Another facility is a 16KHz
fixed frquency setting originally tuned to Rugby Radio Station.
This station was built in 1925 for the transmission of timing
signals for keeping clocks in synchronism. Alas the station was
finally dismantled in August 2007, over 80 years after its first
transmissions on 1st January 1926. Transmissions which ceased
on 1st April 2003 were replaced by signals from Criggion, Powys
which for many years had acted as standby station, however Criggion,
in turn, was dismantled very soon afterwards and transmissions
taken over by Anthorn in Cumbria.
These low frequency transmitting
stations were also used, on slightly different frequencies, to
communicate with submarines as the extremely low frequency (ELF)
signals could be received under water. If you look carefully,
elsewhere on this website I've mentioned this in connection with
my work with Plessey during the "cold war".
Below is the circuit diagram
from the manufacturer's operating manual.
Power is provided from external
batteries. 2 volts for valve filaments, 10 volts for grid bias
and 110 volts HT.
to see an excerpt, describing the 730, from a technical instruction