AVO Multimeter survey

[AdamAnt316]

Thanks for the response. I've read about the cost cutting, as well as the switch from bakelite to thermoplastic coinciding with the MkIV, but have read absolutely nothing elsewhere about any sort of factory refitting of these with the MkV-type case. Do you have any idea when the refit program began, and how widespread it may have been? Mine is the very first MkIV I've seen to which this has been done, but there must be others like it out there.

My guess is that the MkV case is also made of a different type of plastic, or at least one made in a different way, than what was used for the MkIV's case due to the different color and texture. For clarification, what do you mean by "case fixing screws"? Are they of the 'captive' type, meaning that they don't come loose when fully unscrewed, or does it refer to something else? How do they differ from what was used in the proper MkV (and the other later models) to secure the case?

Your theory about the sticker transfer does indeed sound plausible. However, it doesn't seem to explain why the meter in this MkIV almost certainly has the "Ser. No." part printed onto the meter scale, and not handwritten in like the serial number itself. I've looked at pictures of standard AVOmeter 8 MkIVs, and there doesn't seem to be anything whatsoever printed or written below the "8 IV" designation, best as I can tell. As soon as I get the case open, I will look and see what is written on the back of the meter scale.

I am indeed unfamiliar with these AVOmeters, for the most part, and will heed your advice, thanks.

First, I need to figure out a way to remove the calibration stickers without damaging them, though that may not be possible. It still seems quite accurate, for the most part, though the cut-out isn't as sensitive as it should be (fails to trip with the probes applied to a 9V battery with the DC range switch set to 100mA, or in reverse polarity when set to 50µA).

[Phil G4SPZ]

My little sub-collection of DC Avominors has grown by 25% following the arrival of number five; serial number 3597-113. It's a bit poorly, as it is 81 years old, but hopefully it will be sitting up in bed and receiving visitors soon. I believe this to have been made in November 1933 as its serial number is in line with the others in my collection, as follows:

9712-24 (February 1934?)
40955-16 (January 1936?)
73586-943 (September 1943?)
89534-647 (June 1947?)

From these examples, I've established that there are at least three and probably four different case styles used in the DC Avominor. The earliest two have a plain zero-ohms adjuster, voltage ranges of 6V, 120V and 300V, and a straight-sided case. The battery drawer is also different. By 1936, the case had a step all round the bottom edge. And by 1943, they had a zero adjuster incorporating a central socket, voltage ranges of 6V, 60V and 300V, and a range-doubler function which worked on both current and voltage.

If anyone knows of any other variants, please post details and photos!

Phil

[AC/HL]

A change of topic and one follow-up post moved to a new thread: https://www.vintage-radio.net/forum/...d.php?t=107722

[pthomas]

Another AVOMETER to add to your survey

Model 9 Mark 2
No 17693.469

Details: I bought this in mint condition from an auction site. Like all Avos that I have acquired a little work was needed to get it to A1 condition. I am not happy until the instrument looks and performs to perfection! In this case my problem was inconsistent setting of the trip (I put 9v batter across the 100ma DC setting which ought to trip each time. Also I found the pointer was sticking when I applied a reverse voltage (say -9v when on the 10V scale). Needless to say I took the movement out several times (careful not to touch the magnet with the screwdriver by using a piece of cardboard as a shield) and tried the usual thing of examining the gap and hairsprings without finding anything. It was obviously to do with contact of the coil frame with the end stops. The tiniest vibration or even a loud noise would free it and it would zero as normal. Eventually I unscrewed (plastic screwdriver) the tiny plate which secures the pivoted trip lever at the front of the movement. To my surprise I found quite a bit of dirt under this tiny plate and what looked like the remains of grease/oil. Cleaning this up and lightly polishing the tiny metal parts my problems were solved. Once assembled I cannot make the meter stick at all and also it was much easier to set the trip which is now consistent in its operation. Now fixed this meter is super accurate on all ranges I can check and easily betters 1%. Other work I did was clean the glass, repaint the lettering (techniques as described on this forum). I rather like the 9 because of the simpler scale (no dBs.). Another observation is that there does not seem to be any loss of magnetism because I have not needed to adjust the shunt. I think that this is my best Avo!

[Phil G4SPZ]

Originally Posted by pthomas

I think that this is my best Avo!

Another innocent enthusiast bitten by the Avo collecting and restoration bug, then! Join the club...

[Fraser1963]

Hi everyone
I'm a newbie on this forum but have read ALL 60 pages of this thread!
I have a number of Avometers but will start by listing the oldest that I have had for a few years.

No 74-2817
If my reading is right that makes it July 1934?

I generally use my Test Set Multirange No1 for daily messing about, but the 36 range appears to be in full working order and is accurate enough.

[hilitevr]

Hi, just aquired another AVO model 7 s/n 152129-A-550
Very good clean condition,working well after re-positioning and tightening
DC cam.

[pmmunro]

Fraser,

Good to hear from you.

I agree with your interpretation of the date of your 36-range Avometer. This makes it one of the first of the type and a few of the earlier ones seem to have been issued with left-over 34-range instruction plates; is yours one of these?

I hope you found the thread interesting and you will want to let us know about your other Avometers.

PMM

[pmmunro]

Hiltver,

Good to hear from you again.

Do you know anything of the history of you newly acquired Model 7? With you experience I expect you found the fault quickly but I would think quite a few Avometers with the same fault have been scrapped as "uneconomical to repair" through ignorance and lack of interest.

It's good to know yours has found a good home.

PMM

[hilitevr]

Hi, PMM thanks for reply.

Sorry, no history, just an ebay purchase.

The meter is in very good condition, dosn't look like its ever been opened.

Solder joints all original, no added components, all internal screws still covered with original varnish and the movement balance is spot on.

Definitely one of my best purchases.

[Fraser1963]

Hi PMM
Thanks for your reply.
I am unable to tell if the 1934 36 range has the earlier 34 range instruction plate as it is very worn in just the wrong place! See photos attached.
As you can see it is well used but I'm pleased to say in good working order. I haven't opened the case as all is well. I noticed that there appears to be a red fabric seal between the front and the case unlike the rubber O ring on later models. If you would like any more photos please let me know.

I'll list the other 7? Or 8? Avos I've given a home to soon.

Thanks again, Fraser.

[pmmunro]

Fraser,

Thanks for the further information; could you also send pictures of the front and back please?

The red fabric seal was normal at this time and is obviously intended to exclude dust rather than moisture. Avometers were being used in distant parts of what was then the British Empire in 1936, so I don't think it was long before this form of seal had to be re-thought.

The serial numbers of all your other Avometers would be of interest, together with any features which you consider unusual.

PMM

[pmmunro]

Trevor,

Congratulations on your acquisition. Another good Avometers and deserving owner united!

PMM

[Fraser1963]

Hello again PMM
Sorry about the mix up. I thought I'd attached 3 photos, but obviously not!
Here's the next one of the July 1934 36 range
Fraser

Mod edit: There is a delay due to Moderation, that is why your posts may seem to get lost, but they do appear in time.

[AdamAnt316]

Hello once again. Went back to the same surplus store where I found my modified 8MkIV, and bought one of the 8MkVs they had left. Serial number is 0530417, with no sign of a date code listed after the 8V on either of the stickers. Not sure what it is with me and mystery AVOs...

As for the aforementioned 8MkIV, I finally got around to opening it up, and there are no serial numbers written on the back of the meter scale, as best as I can tell. Instead, there are several dates, both printed on a sticker and handwritten on the back of the scale, spanning from the mid '80s to the early '90s. Maybe the sticker is covering up the serial number, but I doubt it. I will take some pictures next time I have it open.
-Adam

[Fraser1963]

Hello again PMM
Sorry about the delay.
Here are the serial numbers of my other Avometers:-
Model 7 No 55521 with date sticker 7/5/71
Model 7 No 78968 with date sticker 7/11/77
Model 8 MK11 on front but Model 8 MK 111 on instruction plate? No 125093-c-761
Test set No1 High sensitivity No 1358 (handwritten on bottom left of scale) ex RAF
Model 7X No 96934-A-665 ex RN
Model 8 MK11 No 5065-c-1063D ex Marconi Co Crack to case and loose glass but all works.
Model 8 MK111 Original No 12283-565 overwritten then handwritten 37943-266 also ex Marconi Co. Currently non-responsive but movement free. To be investigated when time allows.
Model 8 MKV No 13308 8V/5/74. Working order but a bit scruffy.
Hope this of use to you in the survey.
Fraser

[Phil G4SPZ]

Another old DC Avominor has joined its younger colleagues in the workshop. This veteran has the early pattern straight-sided case and plain zero adjuster, and bears the serial number 1873-103, which I'm tempted to think was made in October 1933. Its low serial number seems to fit logically with the others I have of this pattern, 3597-113 and 9712-24, and one here which is 3232-113.

If my assumptions are correct, this latest acquisition is one of the first DC Avometers made, and certainly the oldest in my collection and it will be 81 this October.

[noble kiwi]

Kia ora Phil G4SPZ,

I have a similar Avominor serial number 42131-76. Based on your reckoning, this would mean that it was produced july 1936, which would again tie in.

The leatherette covered case is slightly different than the one held by Richards Radios. The lid is hinged with a single piano hinge rather than two hinges and the opening slopes toward the front so as to expose the bottom part of the meter. The meter sits above the bottom on spacers, so as to provide a section underneath where the leads are stored. I am almost sure that I passed on the serial number for the records some time ago.

Trevor, NZ.

[Phil G4SPZ]

Tena koe Trevor,

This is what I find most interesting about collecting Avometers - the numerous variations in production which caused the shape and style to change, sometimes significantly, throughout the production life of the same instrument.

My 1936 DC Avominor has the serial number 40955-16, which makes it January of that year. Yours of July left the production line some 1,176 meters after mine, which suggests that they were producing around 2,300 a year, well down on the numbers they produced immediately after launching the Avominor in 1933.

Has yours got the 'stepped' Bakelite case, or are its sides completely flat? I ask because I have four of the black Rexine-covered carrying boxes, of both types you mention, but only the straight-sided cased Avominors will fit into them. Of course it's likely that boxes and meters got interchanged, but I'd be interested to know when Avo adopted the later 'stepped' case. It was definitely before they adopted the later zero-adjust knob with the socket in it.

Ka kite ano,

Phil

[noble kiwi]

Kia ora ka pai Phil, LOL

My Avominor has flat sides except for a slight flange at the base forming a very slight plinth.

When I was engaged within in the commercial world it was the hand-built as opposed to production characteristics of the Avometers that intrigued me and lead to my collecting.

Cheers, Trevor.