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Two-valve TRF Reflex battery receiver
Type R.B.I.B Long Range Model M.19, made by Marconi's Wireless Telegraph Co, Ltd. (the chassis of the early models was made by Plessey, Holloway, London). The radio is housed in a polished mahogany cabinet bearing the BBC stamp and GPO Registration No. 0175, and a Marconi-logo on the lid.
On the right hand side of the cabinet there are a number of binding posts for two sets of headphones (or a loudspeaker) and the binding posts for filament and anode voltages. On the left connecting leads for antenna and earth. A reaction control unit with a lever can be seen on the right.
Originally this circuit used "R" type bright emitter valves which were susceptible to failure due to the very high temperature of the filament. A rheostat was provided to control the filament current and thereby prolong the life of these expensive valves. Later sets - like this one - retained this rheostat when "D.E.R." (Dull Emitter Receiver) valves were introduced. The rheostat is operated by a control rod protruding from the left hand side of the cabinet. When the rod is pushed right in, the filament circuit is disconnected from the accumulator.
The price of the radio was 24, including 1 15s for BBC royalties and 12s 6d royalty per valve to Marconi.
Better loudspeaker reception was possible by using an additional two-stage amplifier, the A2, brought out in 1924, or the earlier NB2 with bright emitters.
Tuning
A number of plug-in tuning range blocks were available to cover wavelengths from 300 to 2900 metres. Each block contains two "pancake" coils which provide aerial (antenna) and RF amplifier anode-tuning respectively. A pair of rods with tuning knobs project through the side walls of the cabinet, one to the left and one to the right. To the inner end of each rod is attached a copper plate or spade. As the rods are slid in and out of the cabinet the copper plates are caused to slide across their respective pancake coils and thereby influence the tuning. The following list from a contemporary publication gives an insight into what one could receive using the blocks originally provided with the set:
300-390 m British broadcasting
390-530 m British broadcasting
550-700 m shipping
700-900 m aircraft
2500-2900 m Paris
This set still has two tuning range blocks: 390-530 m and 1300-1700 m.
Operation
The aerial (antenna) is connected, depending upon its length, to the appropriate "Aerial" terminal, 1, 2 or 3. Aerials have a certain natural capacitance to ground and the longer the aerial the greater the capacitance. This capacitance appears across the aerial tuning circuit, thereby affecting its resonant frequency. Now the aerial tuning circuit needs to cover much the same wavelength range for aerials of substantially different lengths (and therefore different capacitances). Medium length aerials (of approximately 15 m) are connected to terminal 2 and thence via a coupling capacitor to the aerial tuner. Aerials much longer than this (up to approximately 30 m) are connected to terminal 1 where a smaller value of coupling capacitor is used which reduces the capacitive loading on the tuned circuit to roughly that of a 15 m aerial. Short aerials are connected to terminal 3 where the act of inserting the aerial plug causes a capacitor to be connected between the aerial and earth, raising the overall aerial capacitance up to roughly that of a 15 m aerial. In this way the aerial tuning circuit is always loaded by roughly the same aerial capacitance. Hence the range of wavelengths covered remains substantially constant for different lengths of aerial.
The first valve amplifies the RF signal from the aerial tuner and the output from its anode is tuned and fed to the second valve which is wired as a grid-leak detector. The grid-leak resistor is marked 2Ω which is the archaic way of writing 2MΩ. The output from the detector anode contains the recovered audio signal and a certain amount of the carrier wave RF as well. This RF output is series tuned by the regenerative unit and fed back to the detector input with the correct phase needed to achieve positive feedback. The setting of the lever on the regenerative unit influences the strength of feedback and hence the selectivity of the circuit.
The audio output from the detector is connected to the (low impedance) primary of an LF feedback transformer. The audio output from the (high impedance) secondary of this LF feedback transformer is connected to the grid of the first valve via an RF choke. The first valve then amplifies this audio signal before coupling it to the headphones via another RF choke.
Data Valves  
Serial number 7855
Dimensions (hwd) 27 32 18.5 cm
Made in 1923
Purchased in 2008
Voltages 1.8 / 45 V
   

Click on a valve for more information

Circuit

What was broadcast in 1923?

 

Listen to "You'll Hear Me Calling Yoo Hoo" by the orchestra of Jack Derrick, recorded February 3rd, 1923

Front view
The set has a pair of detachable panels at the front. The top panel features two viewing portholes which were used to keep an eye on the filaments of the Osram D.E.R. valves. The bottom panel is held with two screws and covers a void where the HT battery could be housed.
The sockets for antenna and earth. The sockets for phones, and filament and anode voltages.
"Dull" emitters still produce a reasonable amount of light in the evening...

Advertisement for the Marconiphone V2

Advertisement in Modern Wireless, August 1923

Two pictures of a Marconiphone V2 with Sterling loudspeaker in a contemporary living room

This page was last edited on 27.04.2019