These sets in the first instance were designed and manufactured for the R.A.N. and R.A.A.F. The differences in type numbers reflected changes to cater for a variety of different applications.
The general purpose receiver covered 1.5 - 24 MHz in 4 bands. These were 1.5 - 3.0, 3.0 - 6.0, 6.0 - 12.0 and 12.0 - 24.0 MHz.
The identifier AMR300 did not come into being until 1945 when the US services required a HF communications receiver - this set improved on the previous models and included temperature compensation of the local oscillator and Faraday screens to enable the set to be used successfully with direction finding systems.
The valve line-up is as follows:
|V1||6U7||1st RF Amp|
|V2||6U7||2nd RF Amp|
|V4||6U7||1st IF Amp|
|V5||6G8||2nd IF Amp and 2nd Detector|
The IF frequency is 455kHz. In its original form, the audio output was 40mw into 5000 ohms connected across one phone jack and 2 watts at 600 ohms across the line terminals.
The oscillator stability is, after 10 minutes warm up, less than 0.05% of the operating frequency on any range.
The sets were designed to operate from either 240 or 110v AC (62 watts), while a separate vibrator supply was available for 12 volt DC operation.
The set weighs 74lbs, appx 34 kg.
The HT line at the output tube was appx 230v dc, with 215v ac being applied to the plates of the rectifier.
The receiver was in high demand by radio amateurs and short wave listeners after the war and commanded high purchase prices from disposal outlets. Unlike other sets of similar performance produced during this period, the AMR300 series did not use plug in coil boxes, which made them easier to use and somewhat tidier!
© Ian O'Toole, 2009. Page created: 01/07/03 Last updated: 27/10/2012