This consists of one of each of the following:
|HF receiver||Type 78|
|HF transmitter||Type 53|
|MF receiver||Type 76|
|MF transmitter||Type 51|
|Modulator unit||Type 76|
|Aerial tuning unit||Type 126|
|and two control units||Type 260 (Air Gunners)|
|Type 276 (Observers)|
All of the equipment together is known as "Four Square", while the HF station is known as "Two in Line".
The units are housed in matching cabinets, which slide into a rack, engaging with 12 pin Jones plugs at the rear. The modulator unit houses a 26 volt rotary transformer which delivers 500 and 250 volts. Heaters are wired for 26 volts dc.
The receiver consists of EA50 diode limiter, EF50 RF amplifier, 6J5 local oscillator, 6K8 mixer and an EF39 crystal calibrator, using a 100 kHz crystal in a Hartley circuit.
Output is taken at 560 kHz from the receiver to the modulator chassis, which houses the IF and Audio stages. The unit can be used as a short wave converter into another receiver at 560 kHz, such as the command Q'5er.
In the Type 76 modulator unit there are two EF39 IF amplifiers and an EF39 BF0, with a 6R7 duo-diode-triode as detector, AVC and first audio amplifier. The output stage is an EF50 single ended audio amplifier with a transformer providing various impedance taps for headphones.
The receiver also features a plug in Desynn motor for remote vernier control of the local oscillator frequency.
© Ian O'Toole, 2009. Page created: 28/04/03 Last updated: 3/12/2009