The R 107 is a high grade general purpose HF communications receiver intended for use in vehicle or ground stations.
It operates with its own built-in PSU from 12 volts DC, or 100 to 250 volts AC, with an internally chassis mounted switch to change over supplies. An internal loudspeaker is fitted with sockets for headphone output.
It is a large and heavy set weighing in at 96lbs and measuring 24" x 13" x 17" deep.
Frequency coverage is from 1.2 - 17.5 Mc/s in 3 bands with operating modes of AM and CW.
Two selectivity bandwidths are provided: Narrow: 3kc/s, Wide: 6.8 kc/s, both at -6db. An AF CW filter centred on 900 c/s is also fitted.
With the exception of the 6X5 rectifier only two types of valve are used. Four EF39s in the RF and IF stages, Four AR21s as local oscillator, BFO, detector and both audio stages. The amount of audio available demonstrates that it is not necessary to use high current tetrodes in output stages, as is the practice with some manufacturers.
Balanced aerial input terminals, transformer coupled plus a high impedance single wire input are provided. Both can be tuned by the aerial trimmer. Sensitivity is listed as 2 - 6 microvolts on AM. My set would better this on most bands. From a practical user’s point of view I have always been more impressed with the R107's sensitivity than almost any other set. Although fitted only with a simple diode detector, SSB resolution is very effective providing the RF gain control is backed off.
An internal relay for muting the R107, when it is used with a transmitter has its connections brought out to the muting plug on the front panel. Shorting these pins will mute the set. A test panel accessible from the front of the receiver allows routine monitoring of the working voltages of all stages without dismantling.
It can be a physically difficult set on which to work, due partly to its weight but mainly to the quality of its construction. Every component is securely fitted, many with "p" clips and screws sealed with shellac varnish.
Reliability is second to none!