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  This TRF receiver, designed in the early 1930s was used in ships until superseded by more modern superhets.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 arrangements.

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 mislaid?

 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 control.

 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.


 Click to see an excerpt, describing the 730, from a technical instruction handbook

Read about the problem of interference on marine receivers

 The Marconi 730 was also used for listening to enemy transmissions until being superseded by the more advanced DST100 borrowed from the Army.


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