Admiralty B40 - Murphy Radio
Written by Bryce Ringwood   

This is the radio that nearly bankrupted Murphy radio. It began to make its appearance on the UK surplus market in the 1960s, competing with imported Japanese radios. Nowadays, we think of Japanese=Quality, but it wasn't quite so in the '60s. Then, Japan was able to flood the market with cheap imports, sending many well established firms out of business.

The B40 uses unfamiliar and quite hard-to-get “CV” valves, most of which are on an 8 pin base. (B8G, I think). It is a fairly large and very heavy radio. It has a small internal speaker of poor audio quality and indeed the entire audio on my set and others I have heard is not very good.
 
In common with the AR88 and the Eddystone 940, the set has two RF stages. It has 3 IF stages and variable selectivity using a half-lattice crystal filter. The set has a built-in crystal calibrator. Frequency coverage is from 0.55 to 30MHz in 5 wavebands. There is no signal-level meter.

Tuning is accomplished via a gear (and chain)-driven reduction drive with all manner of anti-backlash mechanisms. It can be quite tiring tuning from one end of a band to the other - but on the other hand, the tuning scale length is extremely long. The wavechange switch activates an enormous tuning turret and needs some strength to operate. Other controls are : Noise limiter; AGC, IF and RF Gain (Referred to as RF Gain and Anti-Cross Mod, respectively); Selectivity; Mode (R/T, CW, Calibrator). There is a separate volume control for headphones. The set can use crystals and has a multi-position switch. The intermediate frequency is 500kHz - so no huge feats of mental arithmetic are needed to calculate the crystal needed for a particular receive frequency.

There is a “Radar Interference Suppression” circuit, which is of no use unless you are on board a battleship. The battleship tat this model origiinally belonged to was “HMS Collingwood”. This sounds impressive, but I later discovered this to be a land-based station. The set was given to me in non-working

condition, but all it needed was a new mixer valve. Once it was working, I noticed it had a really annoying backlash in the tuning mechanism. The previous owner said he was “used to it”. Examination of the drive mechanism showed that there shouldn't be any backlash. Eventually, I traced the problem to a grub screw that wasn't as tight as it should have been.

This particular radio does suffer from warm-up drift. I don't know if its endemic to all B40s. All in all, its an interesting design from an appearance and technical perspective. There is also a B39 long-wave receiver, which I would really like to own one day.

 
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