AVO Multimeter survey

[The Philpott]

Pete's comments regarding lack of evidence that the versatile Model 'D' was provisioned to
motor vehicle and a/c fleets of the Army or the Navy has set me thinking of possible scenarios.

With the ascendancy of the core of fighter and bomber command in the govt's mind as a real war weapon rather than just for recce, artillery spotting and nuisance/riot suppression, i can't help wondering if old, cumbersome or slightly inferior equipment from the RAF was officially offloaded onto the Army and RN workshops after the D and E had been supplied to the RAF as modern 'high quality' replacements.

[Sinewave]

Originally Posted by The Philpott

'Hands free' version of Avometer Model 47a, using Model D parts

Success. One very shy Avometer. No good meters were cannibalised during the making of this prototype!

Normal V & A ranges are available with K arrow facing East, Low Ranges are available with the arrow facing West....well almost. I have accidentally engineered the arrow to be 'off' by 5 or 6 degrees- which turns out to be a good thing as it is a visual reminder that the meter should be returned to Normal range after being used. Functions unaffected.

Notes:
Screws on rear of 'K' knob could not be tightened without causing K to be immovable. I settled for medium loctite and just nipping them up very slightly.

Parts used:
K knob, ball and spring, brass disc c/w screws, leaf spring and extra leaf spring screw.

Whenever the back is taken off an Avo with a Q adjuster, the contacts should be cleaned and checked. I would say it's one of the most common causes of annoying intermittency.

Dave

Very true. I still haven't finished one of my Avo 7's with the intermittent issue. It's been a few weeks since I had the chance to look at it.

[The Philpott]

K=2 problem solved...Having put away a Model D i had given up on, i finally managed it yesterday.

K=2 was behaving intermittently and eventually failed altogether, yet whenever i checked for a break in circuitry nothing could be found. It turns out that removing the movement shifted a wire slightly and closed the break..and the fault vanished until it was refitted.

The P winding is wired to the little lozenge shaped contact pad in the K switch however there was a (dry!) solder joint concealed within the insulation sleeving. The black woven waxy insulation comes off very nicely if the end of the wire is heated a little. Otherwise it tends to be locked solid onto the wire.

I reused the original scale plate, but mated it to an alternative movement- and was surprised to see that accuracy is maintained and the scale shape matches the arc that the needle describes.

[The Philpott]

'Q' winding:

Salvaged winding destined to replace the damaged one in my 47A(s), WWII era.

Impressed by the efforts to impose linear response- two different alloys and a taper for each. The silvery section amounts to approx 8 ohms and the darker section approx 58 ohms. The meter facia is moulded precisely to accept the tapers.

[Phil G4SPZ]

That type of winding is also seen in the Avo Twin Panel Valve Tester's 'set mA/V' pot. I know, because I managed to fix one once! Avo were past masters at winding all sorts of weird and wonderful bespoke wound components. I'm always impressed.

[The Philpott]

I have noticed the thread on the rear of the Q prod is of significantly larger diameter on these Admiralty meters than it was on the older Model 7 i worked on last year. Around this manufacturing period it appears there was also more than one length of coil spring fitted to 'Q'- although this could simply have been down to picking from the wrong parts bin.

I can well believe there would have been incidences in service of a TWANG followed by small bits floating around inside and jamming the switches. A diagnosis of this would be easy as the Q knob would simply lift out from the front!

[Superhet Si]

I have a Model 1 (Test set Multirange No.1 High Sensitivity 1143.167.

[The Philpott]

..Even the R knob can be wonky on occasion. Someone had overtightened this one to try and overcome it..which never works, of course.

[Superscope]

Ok, since this Thread started off as a Serial Number Survey, I thought I would ask a
Serial Number Question!

I picked up a quite nice Model 8 Mk V at the weekend, still in it's Case with Leads and Manual, but the Serial Number is a bit odd and I am hoping somebody on here can enlighten me!

I always thought the last Two Digits of the Serial Number gave us the Date of Manufacture (Actually the Date of Calibration as I understand it).

However, the serial number on this Unit is:
No 042635
8V

I can't see how the 35 can relate to a year!
What am I missing?

This Meter has retained it's Label on the outside of the Case and the same Label inside the Battery compartment, both are identical, so the Number is not in question.


What am I missing here?


Ian

[Sinewave]

Come the mark 5 (as with the mark 4's) the serial number is a little different.

Are there any other numbers after the 8V?

They usually say something like 8V/3/77 afte the serial number. The 8V meaning model 8 mark 5 of course, then the last two section of digits being the date.

[Superscope]

Unfortunately Not,

After the 8V there is nothing, just a blank space.

So I'm guessing then, that even with a Label, the Date of this Unit
is indeterminable?




Ian

[Sinewave]

I have a few that like yours have no date. Unfortuately yes this means the date will remain a mystery.

Infact I even have one or two with no serial number sticker on there at all, or even damaged stickers.

[Superscope]

I can understand a missing or damaged Label with equipment of this age, but to have an intact Label without the Date, after 70 odd years of identifying the equipment this way
just seems odd.

I wonder why AVO did this.

I have a Post Office 8V (MMR 14C) with the same black Label style, clearly showing
the Date after the 8V.
My later Mk VII although having a different style Sticker, still clearly shows the Date.

So I wonder if this was just a glitch in production?


Ian

[Sinewave]

Over all the Avos I have, there are differences in the serial writing/stickers. Some numbering formats look different. I don't know why.

[Sinewave]

I picked this up a few days ago.

Wow, 30V batteries! These batteries need replacing if I'm to use this range extender, but otherwise a nice addition to the collection.

I simply could not resist

Resistance to this purchase would be futile

I'll get my coat....

[pmmunro]

Sinewave,

I'll resist the temptation to extend the range of your puns....

You may have to make up your own 30V batteries if you want to use the high resistance ranges. I've used the low resistance ranges of one of these successfully but the procedure is a bit involved compared to a continuity meter. Although these units do not seem to be too rare, I wouldn't have expected too many to have been sold. It's a pity they don't have serial numbers which would help judge how many were made.

Of course now you'll have to find extension units to suit your Model 7, 40 and Avominor instruments as well.

On the subject of meter serial numbers, the system has changed several times over the years but began to be difficult to interpret in the Thorn era of the early 1970s when the date had no obvious relation to the serial number. The self adhesive labels are often too badly worn to read but may be duplicated inside the battery compartment.

Perhaps Andy Gilham might be able to enlighten us on the serial number system of the later meter types?

PMM

[Pamphonica]

By enormous good luck, NVCF turned up for a total outlay of less than £30 no less than three 36-range ("Model 5") Avos. Two are working (one a bit down on cal, one faulty on ac) plus one that's definitely a parts-only machine as it's missing terminals, fuse and has a totally stuck and badly re-painted movement. But a spares source is always useful...

No-one seemed to want them. Two sat on the Bring & Buy for hours, and the last one I bought as the show was closing.

They rather nicely complete my pre-war line-up. I had no 36-Range meters at all before.

I'll add them to the database shortly.
I just noticed that they are 1 month apart and 100 serial numbers apart. A production of 100 meters a month, roughly. Not bad!

Jeremy

[pmmunro]

Congratulations Jeremy on your latest finds. It's good to know they've gone to a good home. You have to wonder where they all come from, seventy or more years after they were made. Perhaps they were brought home by someone who thought they might be useful some day when they were no longer wanted by the original owner, having been stored away "just in case" for years until finally the space was needed for something else or the premises closed down.

It's also strange how some models appear still to be reasonably readily available while others are not. Short production lives, such as the 34-range Avometer, can explain some of the scarcity but others, such as the dearth of pre-1939 Model 7s, are harder to explain.

PMM

[The Philpott]

i did see the resistance range extender for sale but couldn't justify the shed space for it (not to mention making up the batteries.)

I's nice to see these acquisitions are to be brought up to spec. rather than purely ornamental.

I theorised that early Model 7's being conspicuous by their absence, might have been due to a factory recall. As i have mentioned,the build quality of mine is inferior to the military contract 'D' or Admiralty meters i have seen. I'm not sure we'll ever know Peter....unless Andy finds something relating to it. Not found anything relating to the OY testmeter yet. but will keep eyes open.

Dave

[Phil G4SPZ]

Originally Posted by pmmunro

...You have to wonder where they all come from, seventy or more years after they were made...

I'd like to add my thanks to Jeremy for re-homing the two 36-range Avos that I brought in to the NVCF Bring & Buy stall! From memory, the 'working on DC' unit was bought by me several years ago, and I probably reported its serial number via this thread at the time. It went into the 'to-do' pile, but it remained there because shortly afterwards a much better and almost fully-working example became available, which was fixed and is still in my collection. The 'parts only' unit was given to me by Paul Adams in exchange for some repair advice.

The main usefulness of the 36-range is its low ohms range, calibrated down to 0.1 ohm. Don't try checking PN junctions with one, though - it injects up to 200mA