Receiver R1155

The R1155 was developed in the very late 30s for the RAF and entered service in 1940. It was a vast improvement over the existing equipment and was frequently retrofitted to aircraft with previous generation equipment. It was not developed as a straight communications receiver but was part of an aircraft system intended for both communications and direction finding, and therefore had circuitry and controls for D/F (Direction Finding). Only headphone output was provided, as loudspeakers were not practical in an aircraft with four roaring Merlin engines! The set was powered externally from the aircraft electrical systems.

It was used together with the companion transmitter T1154 in a wide range of aircraft including the Lancaster, Halifax, York, Varsity, Mosquito, Valetta, Shackleton and Wellington. The complete system for heavy bombers included two R1155s (one for the radio operator and one for the navigator) a T1154 transmitter, an intercom system for the crew and three aerial systems.

Receiver data
The design is a single conversion superhet receiver covering the range 75 kHz to 18.5 MHz in five switched bands (these bands differed according to the model variant). The valve line-up is First RF VR100 / KTW63 vari-mu pentode, Mixer/oscillator VR99 / X65 triode-hexode, 1st IF VR100 / KTW63 vari-mu pentode, 2nd IF VR100 / KTW63 vari-mu pentode, 1st audio amp & detector/audio VR101 / DL63 double-diode/triode, BFO oscillator & AGC detector valve VR101 / DL63 double-diode/triode, Tuning indicator valve (VI103 / Y61) making a complement of 7 valves for the communications circuit. There is also a D/F circuit which used 2 triode-hexode (VR99A / X65) valves and 1 double triode (VR102 / BL63) valve. The magic-eye was shared between the communications and D/F circuitry.

The R1155 has a peculiar power requirement in that the 220V HT is floating. The set acts like a potential divider with the valves and screen supplies acting as one part, and a couple of large resistors acting as the other part. The middle of the potential divider is connected to the chassis, as is one side of the heater supply. The -ve side is used to for the valve grid bias supplies. With a supply voltage of 220V, the +ve HT line is at 184V to190V and the -ve HT line at -36V to -28V. The actual voltages depend on the setting of the RF gain and the particular values of the resistors. If the RF gain is high, the -ve bias on the valve grids is low and the valves conduct, lowering the voltage drop across them.

It continued essentially unmodified through its production life, apart from the addition of various traps to counteract interference from RADAR and MW stations. There were problems with the original tuning knob and Ekco developed an improved epicyclic slow motion drive, which was fitted as a replacement to many existing sets. The BFO valve tended to overheat and the problem was solved by making a hole in the BFO compartment cover to let the heat out. Approximately 80,000 R1155s were manufactured. The receiver sensitivity is quoted as 9 to 10ÁV for a useable audio output.

The picture shows an R1155 (top) and below it, one with its companion T1154 installed in the Brooklands Vickers Varsity.