Avo Universal Testmeter No. 107 (O.Y Meter)

[AndyGilham]

For those Avo enthusiasts, especially Peter Munro, since I know he has asked about this product. I have attached a schematic of the Avo Testmeter No. 107, commonly known as the O.Y. Testmeter.

This particular document is dated 1951 and based on the Model 8, however there was a second variant from 1961 based on the Model 8 Mk 2.

[The Philpott]

Thankyou Andy, that is interesting. It seems to have some features in common with both the Model 8 and also the HR Avometer which preceded it.

Only coverage up to 1A on DCA, and no AC current facility. 1.5v and 15v on board like a Model 8, compared to the HRM which has 1.5v and 4.5v.

Have you a picture of this type of meter?

Dave

[The Philpott]

Yet more avometer weirdness. I wouldn't be surprised if this one is a highly endangered species. (pics courtesy of PMM's original query)

Viz:

[pmmunro]

Andy,

Very many thanks for finding and posting this information.

Do you know the customer for whom this meter was designed and made and what it's intended use was please?

Any further information would be of great interest.

PMM.

[The Philpott]

Ok, so AC current measurements not required and only small DC current measurement required. A bit of weight has thus been saved,...... a fairly specific role at high altitude?

Aside from being in the heart of the cold war, my first thought was in connection with certain Lancasters that avoided being shot down or melted down, were employed testing first generation jet engines. There are some interesting in-flight photos of Lancs with (feathered!) Merlins in two nacelles, and powered up (Nene?) engines in the other two. Also seen was a 4 Merlin Lanc with a prop-jet in the nose. Prototype fins were also installed on the rear fuselage of the BBMF's current Lanc, in it's former life. But this then got me into wondering why the military arrow is in place- wouldn't engine testing would have been sanctioned by the engine & a/c manufacturers, independent of the military? Or perhaps this was a joint venture. The lack of high DC current coverage could have been provided by dedicated ammeters within the test rigs.

My second thought was MET a/c (Lancs and B17's for example) with delicate testing equipment aboard, exploring things such as fledgling knowledge of the jet stream, and wing/carburettor icing. Would the MET have been using military contract equipment? Probably.

Sub-hunting Shackletons and V bombers are another possibility, (a lot of complex equipment aboard)

That adjustable mounting with 90 degree detents on the side is intriguing.

I do wonder if Radium paint was used anywhere on the instrument, to make things easier to see.

Dave

[AndyGilham]

I am afraid, apart from the drawings, I have no other information on this product. So details on its use and who these instruments were sold too is an unknown.
I still have much data to trawl through, so something may come up in the engineering note files! Time will tell.

Andy

[Sinewave]

Originally Posted by pmmunro

Do you know the customer for whom this meter was designed and made and what it's intended use was please?

Any further information would be of great interest.

PMM.

It has a NATO marking on it, so will assume a military type were the customer.

[The Philpott]

Absolutely, it's MOD in some form, but the functionality is less than that of a standard Model 8 (apart from the lockable REV MC function which appeared in a slightly different- but still rotary- form on some militarised Mod 8's.)

The mystery is quite what contract this lashed up 'special' fulfilled, and what was the arena of usage. Perhaps some things are destined to stay a mystery- we may never know!

Dave

[Sinewave]

It's interesting how some variant of the 8s differ, such as test set no. 1 having no 500Vdc range and others of limited ohms ranges.