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Old 2nd Nov 2020, 11:21 pm   #2721
Rileyman
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Default Re: AVO Multimeter survey

I was reminded the other day that I hadn't yet published a list of my AVOs , so here they are .
Please note :-
(a) I'm an Engineer rather than a Collector , and these excellent
instruments are my tools . With the exception of Item(6) they are in
use just as often as I use (say) a soldering-iron , wire-strippers ,
Whitworth spanners , or a Micrometer .
(b) Item(7) may well already have been recorded .

(1)Mod.8 MKll Ser,No.5294C/1063D Issued to me in Oct. 1963
(2)Mod.8 Mklll Ser.No.79311/468 Issued to me in Apr. 1968
(3)Mod.8 MKll Ser.No.69818/C/158 Movement went o/c in Feb. 2016
(4)Mod.8 MKll Ser.No.119927/C/361 Allocated to my workshop .
(5)Mod.8 Mklll Ser.No.78359/468
(6)Mod.8X Panclimatic Ser.No.71988/C/358 A.P.12945A engraved above
Scale window. Case beige(?) hammerfinish . Bought for spares ,
Movement now in Item(3)
(7) AvoMinor , Air Ministry Testmeter Type "E" No. E 1929 1944
A Christmas present (2017) which arrived cleaned , overhauled ,
calibrated , and housed snugly in a "DOVE MEN CARE" tin .
Fits nicely in the glovebox of an old Riley .
I was so chuffed that I hadn't the heart to protest when the donor
later appropriated a photo I'd emailed to him (to confirm that my
Tek.547+1A4 Plug-In was now firing on all cylinders) ----- and
used it as his avatar !

Laurie .
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Old 3rd Nov 2020, 2:29 pm   #2722
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Default Re: AVO Multimeter survey

Thanks to everybody for the Recent Serial Numbers.
All now recorded in the Database.


Rileyman,

Can I confirm the Serial Number of your Avominor AM Type E.

Is that the Full and correct serial Number?
1929 seems a bit to low for a 1944 Meter.

Is there a Digit missing on the end maybe?
1929x would fit in exactly with a 1944.

1929 if correct, would be more in line with a 1942 Meter.





Ian
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Old 3rd Nov 2020, 4:00 pm   #2723
The Philpott
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Default Re: AVO Multimeter survey

Ian, it is an anomalous number (i passed that meter to RM!) but i have concluded from seeing other 'out of step' serials that there was a second production line (possibly a shadow factory) - meaning at least 2 number series for the Type E running parallel, so to speak.

Dave (avatar appropriator...)
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Old 3rd Nov 2020, 4:23 pm   #2724
micheal
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Default Re: AVO Multimeter survey

Hi guys, i can confirm i still have 206-108 in my collection

Mike.
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Old 3rd Nov 2020, 9:31 pm   #2725
The Philpott
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Default Re: AVO Multimeter survey

ACWEECO Anti-tamper seal

(is this what they call stockholm tar?)
A rather gritty black mixture, softer than coal.

If you stare for long enough, the A V and O become visible! They are bevelled, and raised off the surface of the seal.

Dave
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Old 3rd Nov 2020, 10:47 pm   #2726
Rileyman
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Default Re: AVO Multimeter survey

Ian , Just read your query .
I've looked at the scaleplate using a 10x glass , and can't see owt suspicious , but as I've never before had reason to do so I have nothing to compare it with .
Best I can do is to send you a photo (and hope it is free of camera shake !)
I have minimal experience of the procedures involved ,----- so the Best of Luck !

Laurie .
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Old 3rd Nov 2020, 11:47 pm   #2727
Rileyman
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Default Re: AVO Multimeter survey

Forgot to add that , to me , the "1929" and the last "4" of "1944" appear handwritten , and by the same hand . Would you agree ?

Laurie .
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Old 4th Nov 2020, 2:17 pm   #2728
AndyGilham
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Default Re: AVO Multimeter survey

Quote:
Originally Posted by The Philpott View Post
Andy/Ian

-i know what happened- at the time i submitted data on all those Type HR's that i knew of!

These don't belong to me:

144-98
206-108
404-79
509-640
566-141

I have yet to hear of more Low Resistance Ohmmeters (similar period of manufacture to those HR's) beyond the 2 which are logged...but of course they carry a 1.5v cell so wastage could have been higher. We know 375 or more were made.

Dave
509-640 and 566-141 are in my collection.

Andy
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Old 7th Nov 2020, 3:21 pm   #2729
electricsub
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Default Re: AVO Multimeter survey

Bought Two Avo Model 8 this week.

1- Model 8 III
S/No. 69414-1067

2- Model 8
S/No. 17103-C-953
This one i suspect is a Model I - all terminals are black no red
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Old 8th Nov 2020, 8:37 am   #2730
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Default Re: AVO Multimeter survey

Hi electricsub,

Yes your 2- Model 8 S/No. 17103-C-953 will be a Mk I.

Both the Date (Sep 1953) and the fact it has Black Terminals support this.

The Terminals should be of the Domed Bakelite type without the intergrated
4mm Banana Sockets.




Ian
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Old 8th Nov 2020, 4:19 pm   #2731
electricsub
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Default Re: AVO Multimeter survey

Hi Ian,
Thanks for the response,
That means my Avo8 Mk1 is only 10 years younger than me

Robert
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Old 10th Nov 2020, 10:14 pm   #2732
The Philpott
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Default Re: AVO Multimeter survey

Avominor Type HR s/n 162-108

1- Comparison of 1938 and 1940 meters- it seems later meters lack the large Siemens Halske 20 Meg resistor, either because the factory had run out of them, or run out of ones that were of suitable values to be hand-picked for installation. The 100v range and 1000v range do have a series arrangement in the 1938 meter, the former having a 2Meg (5%) resistor and the latter adding the 20Meg (20%) resistor. (On the 1000v range the resistance measured at the terminals with a UT210 DMM is actually 20.68Meg!)

2- I have never seen a magnetic shunt at this angle in an Avominor- compare with pic 3 -which is what i'm accustomed to. I will be interested to see what changes can be accomplished by altering the angle (which appears to be arranged to restrict the flux by as little as possible. Probably the only way to increase the flux more would be to remove the shunt altogether.)

4- The o/c 50 kohm bobbin can be bypassed with minimal intervention, but the movement itself is rather out of balance in respect of the side and tail weights, so i may well tackle this having done it successfully before.

I have handpicked tiny 1% 1/4 watt resistors of 68k and 180k which are a little high so come out nicely at 50k in parallel. Noted that increase in the 68k resistor had a much heavier effect on increasing the parallel resistance. Stored knowledge for future reference!

Dave
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Old 11th Nov 2020, 10:14 pm   #2733
The Philpott
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Default Re: AVO Multimeter survey

Instructions for DC Avominor
(The nine terminal model, not the eight terminal model or the HR version)

Avominors and their wooden boxes survive quite well, but the same can't be said for the leads, probes, and instructions. In view of this here is the leaflet.

If you make a request via PM, I can send these in a more versatile format via email for anyone interested, however it may take me a week to get round to sending it!

Two more images follow.

Dave
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Old 11th Nov 2020, 10:15 pm   #2734
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DC Avominor:

(A date on the last page...? May 1941?)
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Old 18th Nov 2020, 10:32 pm   #2735
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A light refurb. of a Type HR Avominor- & modifying a magnet shunt

On experimenting with calibration of the magnet, i found that taking some length off the ends of the magnet shunt altered it's suppressive effect on the flux- and allowed me to get correct meter values which would otherwise have been unobtainable without a full remagnetisation, piddling around with very tiny Neodymium magnets, or removing the shunt altogether and trying to mildly demagnetise.. Unwise!

I have covered this in 'success stories', but there were other fixes done to the meter, and i had the camera handy.

The rotating bronze wiper on the pot. was barely making physical contact with the brass contact block, but somehow it managed not to create unwanted resistance. I didn't fancy unsoldering the wiper, kinking it, then attempting to resolder it to the shaft paying attention to the alignment of white line and dot on the front facia! I chose instead to build up the brass block using solder, then file it back to form a nice hump. Success. What little electrical resistance had been there had now gone. I doubt the meter would work well on it's resistance range, but this is not an issue for me (it would need external voltage anyway.)

The movement was somewhat out of balance, and i managed to rectify this by adding car paint, noting that there was no provision for side ballast whatsoever- i had to add it to the moving coil itself. Thus far i have NOT had a problem with my solvent based car paint attacking coil insulation in this type of application.

The glass was still glued in, but patchily so. I added a little cyanoacrylate at the patchy bits, this formed a sludge in combination with the old glue, but it did cure overnight. I would always leave replacing the movement 'till the next day when using Superglue for this, as it creeps over the glass and the fumes leave deposits elsewhere unless open to the air for some hours. Marks removed with Acetone before continuing.

What i thought was a 50kohm bobbin was actually supposed to be a 49kohm- which with the values i had in stock made the addition of a couple of series resistors less tidy than i hoped- but it does the job.

The pointer end-stops were causing a bit of sticking, levering them away from their mounting screws to present an angled obstruction helped somewhat, although these movements do have a tendency to stick at the ends of the scale whatever you do with them. I suppose it's because of the low mass and low torgue involved.

Dave
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Old 19th Nov 2020, 6:56 pm   #2736
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Default Re: AVO Multimeter survey

Well done again, Dave. Thanks for taking the trouble to provide the write-up.

Do you find that using car paint or shellac for balancing has the disadvantage of a change of mass as the solvent evaporates, or have you mastered the technique of allowing a little extra so that the mass is right when the paint is dry?

Wax has the advantage of the mass being unchanged between the molten and solid state but while I have a small stock of wax pastilles of a suitable hard wax type, I don't know its technical characteristics so that I could obtain more if I ever need to.

PMM
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Old 19th Nov 2020, 9:31 pm   #2737
The Philpott
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Default Re: AVO Multimeter survey

Thanks Peter,

Forgot to mention that- I overdo the paint blob very slightly then allow to evaporate- 4 to 7 attempts usually, building a little at a time.
In this case i was forcibly reminded to hold the movement away from my arms and legs whilst tail-balancing as thermals were lifting the pointer making it appear tail heavy..

Dave
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Old 19th Nov 2020, 10:18 pm   #2738
The Philpott
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Question: Do those large Siemens resistors drift with age? I had always assumed that they are wirewounds (and therefore similar in stability to Welwyns)

One 20Meg example measures 21.45Meg (well within the 20% tolerance, but would arguably have rendered the 1000v range 'indication only')

Dave
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Old 5th Dec 2020, 12:49 pm   #2739
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There has been a lot of speculation about a possible Avo Shadow Factory.

Could this Shadow Factory have been staring us all in the Face for years?


There are various references on the Web which say the Vauxhall Bridge Rd Site
was acquired in 1939.
Although as yet, I have not found definitive proof of this.

All the War Time Meters I have seen, all sport a Douglas Rd Dataplate.
The earliest Vauxhall Bridge Rd Dataplate I have, is from a 1946 Model 7.

It could well be, that Vauxhall Bridge Rd was actually a Shadow Factory
throughout World War 2.





Ian
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Old 5th Dec 2020, 4:45 pm   #2740
micheal
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Douglas street is at the back of Vauxhall Bridge Road and was the main customer entrance

Mike
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