AVO MODEL 40 admiralty pattern 48a

[jimbo8400bid]

i have recently inherited an UNIVERSAL MODEL 40 Admiralty Patten 48A it seems to be complete in wooden box (with leather handle and brass furniture), i wish to know more about this item such as age and what it would have been used for and by whom etc.
I cant seem to see a serial number to help with the research. thanks jamie

[SPCh]

The Admiralty pattern 48A is essentially the Model 40 (first introduced in December 1939) supplied in a smart wooden box with accessories (a multiplier and a shunt). The Model 40 was upgraded (along with the Model 7 and Model 8) to a Mk II version in 1956, and is recognisable by the red and black socket terminals which replaced the original knurled black screw types. I have never seen a 48a in Mk II format, so I suspect it was phased out before 1956. Certainly the admiralty was being supplied with Model 8s by then. The serial number may (but only may) give a clue to the date: is there a handwritten number somewhere on the face of the scaleplate, or perhaps a pencilled number inside, on theback of the scaleplate ?

[pmmunro]

The Admiralty Pattern 48A is one of two Avometers which I know to have been supplied to the Admiralty during the 1940s. The other is the Model 47A and there may have been others, but I have no information on this. Both the 47A and 48A are very similar to the contemporary Model 40, except that their resistance ranges are confined to those which depend on a 1.5V cell. The Model 40 used two 4.5V cycle lamp batteries for the higher resistance ranges.

The basic meter is the 47A which was supplied in a wooden box: the 48A came with shunts and a current transformer, all in a larger wooden box. From the ranges, and the accessories, it would be fairly sure that these meters were for use on ships' electrical systems. They would not be ideal for radio or radar electronics as the have a sensitivity of only 333 ohms per volt with the "divide by two" button pressed and 166 ohms per volt normally.

Apart from the restricted "ohms" ranges the only other difference in comparison to the Model 40 may have been some slight modification such as elimination of some ferrous parts and more thorough varnishing to suit the marine application.

I assume that your meter has a front panel which has the legend "Model 40" moulded into it. This appears to have been a war-time expedient to use whatever suitable front panels were available. Panels marked "Model 40" were also used on Air Ministry Type 'D' Avometers although these differ quite considerably from the Model 40.

There should be a serial number at the extreme lower right-hand edge of the scale plate and the last three or four figures are the month and year of manufacture. Let us know what the number is, via SPCH's Avometer survey, if you like.

Avometers were made to Admiralty pattern at least from the late 1930s when the Model 48 was a marine version of the then-current 36-range Universal Avometer. I have not seen a 47A or 48A later than c. 1948 by which time the Navy seems to have had enough to last them until the 1980s. I have been told that one was found with an Admiralty calibration sticker from around 1990, but I can't confirm this.

It is quite probable that the Admiralty bought standard or panclimatic Model 40s later; can anyone advise?

During the 1980s, Digital Avometers, Type DA116 were used in the submarine fleet. I have one which once belonged to HMS Upholder (S-40) which later became HMCS Chicoutimi, which was involved in a fatal fire while making its way to Canada in 2004.

If anyone knows how to get hold of a copy of the Admiralty specifications 47A or 48A, I would be very interested. The same applies to Air Ministry spec. 10A/10610 or 10S/10610 relating to the Model 'D' - this was not exclusively an Avometer - other manufacturers also made AM Type 'D' test sets. I conclude that the 'D' was designed primarily for 6, 12 and 24volt DC, automotive type electrical systems and would have been equally useful for aircraft of the 1940s or motor vehicles. Strangely, it was not until the Model 12, c. 1960, that Avo made a meter specifically for auto-electrical systems.

It is also surprising, if in fact it is the case, that the RAOC or REME did not use the Model 'D' as they had plenty of motor vehicles to service. The Avometer 'D' comes both with a crown with the letters 'A' & 'M' either side at the centre top of the scale plate and with a broad arrow (pheon) in the same place. Does anyone know if this is of any particular significance in terms of Crown property and could the broad arrow version have been for Army use? Both versions carry the AM spec 10S/10610 on the instruction plate on the back.

PMM

[jimbo8400bid]

thanks for all your help. is it worth anything and where could i off load it as i have no use for it myself?

[SPCh]

It's rather too insensitive to be much use for modern (even valve-based) electronics, but they still appear (and sell !) regularly on e-bay. You might get a tenner for it - people will sometimes pay that just to get the box.

If you could find the serial number it would help my survey (see "sticky" thread.

[jimbo8400bid]

cant find a number anywhere on it, but i must say it all looks in very good condition, i will put it on ebay and see what happens!! thanks again

[Dave Moll]

Originally Posted by SPCh

If you could find the serial number it would help my survey (see "sticky" thread.

Your "sticky" thread seems to have come unstuck, but this has reminded to add my AVOs to it.