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Old 8th Dec 2018, 5:26 pm   #1
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Default Avo 36 range restoration

I just bought an Avo (see photos), it seems a 24 or 36 range one.

I will post more photos when i receive it, and we will see the problems and possible solutions.

As i said in the "survey Avo" thread, the battery cover is missing, all the screws are not present.

Superscope has also another 36 range which need attention, as he said, a new thread would be useful.


So i opened this thread to show 36 range AVOs, their problems and solutions.

photos of mine attached.
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Old 8th Dec 2018, 6:29 pm   #2
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Default Re: Avo 36 range restoration

Aitor,

How about getting this Thread started with how a 36 Range should look inside!

I can't take credit for the Fantastic Job done here, but I certainly hope to be
able to do something similar on mine. Not sure I can get it that clean though!
The Standard of work done on this AVO in the Photo's is extraordinary.

I have done a Basic test on the Meter Movement on my sorry example, and
although the Pointer is bent completely out of shape, it does at least respond to a Voltage, so it qualifies for a restoration.
Had the movement been totally trashed it would have to relegated to the Spares Department!



Ian
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Old 8th Dec 2018, 6:46 pm   #3
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Default Re: Avo 36 range restoration

That AVO looks fantastic!!!

So yours is impossible to be repair?

Perphaps we can find the spare parts you need to complete it!! do not give up!!
 
Old 8th Dec 2018, 7:32 pm   #4
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Default Re: Avo 36 range restoration

No, not impossible to Repair!
Quite the opposite, hopefully.

I've not yet had the back off, so I have no idea yet what work will be required.
As a first step, I just applied some Voltage to see if there was a reaction.

To my surprise the Pointer moved, so at least the Movement is basically working, but
the Pointer is so bent, it sits at about 10% FSD at rest, and moves a maximum of
20% before bottoming out on the Scaleplate.


My first question to anybody out there who has a 36 Range, is what is correct arrangement for the P, R & Z Control Knobs?

On that rather nice, almost Mint example in my previous post, all three Controls only
have an exposed Screw Head.
Looking at Richards Radio WebSite, all the Models from 2 to 5 also, only have an exposed Screw Heads.
On the Model 5 I picked up this week there are Plastic/Bakelite Knobs on them, only the
middle Control Z has a bare Screw Head, like the Model 6 shown on Richards Radios.

I am assuming, all three Controls (P, R & Z) should have Plastic/Bakelite Knobs on them,
and if this is true, one has to assume very few survive?

Does anybody know what is correct?

Ian
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Old 8th Dec 2018, 7:48 pm   #5
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Default Re: Avo 36 range restoration

I was wondering the same about the 3 knobs, mines are made of plastic. In Richard’s page they are screws.

Do not know if there are two variants of the same model or if the plastic had came off.

Looking to the photos of the battery cover you load on the other thread (see photos), it seems that is the same cover that Avo 8 but with a piece of metal attached with a rivet.

Can you confirm that ??

If so, it will be very easy to reproduce.
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Old 8th Dec 2018, 8:16 pm   #6
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Default Re: Avo 36 range restoration

I saw that early meter on sale and told the seller it was a Model 5.

I think the battery cover is the same dimension as the later metal type but with the extra rivet Aitor mentions.

On my Model 4 the label on the rear of the battery cover has red printing. Ian's pictures show me what the full text says- mine was damaged.

Note that with a badly damaged scale plate, a later one from Model 40/47A/48A is unsatisfactory as the ohms scale is different. If we could ignore this factor the V & A scales would have a fighting chance of being accurate enough- but no guarantees as the shape of the scale might not be compatible.

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Old 8th Dec 2018, 8:23 pm   #7
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Default Re: Avo 36 range restoration

I can scanner in 600DPI my scale plate for Ian if he needs one.
 
Old 8th Dec 2018, 9:00 pm   #8
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Default Re: Avo 36 range restoration

That's funny, I also informed the Seller it was a Model 5. Great Minds think alike Dave.

She was probably getting fed up with everybody telling Her
But I got a nice Thank You reply, but Aitor had already bought by then.

Regarding the Battery Cover, it is a bit narrower than a Model 8.

The Model 8 is 145mm X 62mm
The Model 5 is 145mm X 56mm

Notice the Way the Label is cut badly. No precision cutting there, obviously just
one of the Workers with a pair of Scissors.

I plan to re-produce the Label when I get time, after I have identified the Font's used.
My other 36 has also lost it's Label.

Aitor,

A Scan would be great, but be very careful, I notice on your New 36, the Scaleplate is
also starting to De-laminate at the Edges.
Nowhere near as bad as mine, but I don't know the best way to protect it from further damage.
Once this starts, the Paint is very brittle especially if it has started to Curl up.



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Old 8th Dec 2018, 9:09 pm   #9
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Default Re: Avo 36 range restoration

Yes, it is difficult to stop the paint damage on the plate, perhaps with transparent nail polish applied just in the damage zone, could prevent it to continue peeling off.

I will scan it for you at maximum definition, after that, i think you can put your serial number with photoshop and maybe we can transfer the image to the aluminium plate again.
 
Old 8th Dec 2018, 9:41 pm   #10
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Default Re: Avo 36 range restoration

I very nearly had one of these, sadly My Hermes lost it
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Old 8th Dec 2018, 11:44 pm   #11
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Default Re: Avo 36 range restoration

I think that is Unlucky and Unusual.
Touch Wood, I've not had a problem with My Hermes so far, Sending or Receiving.
Are you sure the Meter was actually sent?


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Old 9th Dec 2018, 12:37 am   #12
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Default Re: Avo 36 range restoration

Quote:
Originally Posted by Superscope View Post
I think that is Unlucky and Unusual.
Touch Wood, I've not had a problem with My Hermes so far, Sending or Receiving.
You will, as have I on both sending and receiving.

Have a look at the Watchdog insider documentary on them.

Quote:
Are you sure the Meter was actually sent?
Yes
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Old 9th Dec 2018, 1:00 am   #13
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Default Re: Avo 36 range restoration

As I have documented I made an attempt to stabilise an early scale-plate by bonding the lifted edges of the paint back to the plate with car lacquer from a touch-up pen kit. This has been successful- so far- but it did dry very quickly. Any attempt to scan a plate in good condition is a great attempt at conservation.

(Yes Ian, Jane did reply very politely!)

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Old 9th Dec 2018, 5:29 pm   #14
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Default Re: Avo 36 range restoration

I will scan my 36 AVO scale for Superscope and everybody who could need it. After that, i will try to print it in aluminium, that will be the best solution.

Other solution could be to spray a car varnish the whole plate. I should be a very good one, that not suffer color change with the years and that no affect the original paint. But the problem will continue been there, between the original paint and the aluminium.
 
Old 11th Dec 2018, 11:52 pm   #15
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Default Re: Avo 36 range restoration

Scanning a scaleplate is unlikely to give the required accuracy for anything but a cosmetic restoration.

These Avometers' scaleplates were hand calibrated and the radial lines ruled in by "crow quill". I don't have details of the process from this era but later meters, from the 1950s for example, were calibrated against a standard instrument at the 10 (or 12) cardinal scale points and the intermediate divisions were ruled in using a proportional pantograph device. The cardinal points were marked on the scaleplate with a centre punch and the marks are often quite clearly to be seen above the top arc.

The flaking scaleplate problem arises because the scaleplate is plated, presumably in nickel, and highly polished so that the mirror arc is provided simply by not painting that part. It may have seemed a good idea at the time but a little experience would have indicated that paint does not adhere well to polished surfaces. The cost of machining a neat circular arc in the scaleplate blank may have been significant. To judge by the weight, these scaleplate are made of brass. As aluminium was used for the backcases, it was obviously available, but it too is not easy to paint unless an etch primer is used.

I suspect that damp exacerbates the problem of flaking and no responsible person would have left a valuable instrument exposed to damp when these meters were new, given that they cost around a months wages for the average user.

One of my original Avometers has some slight flaking damage and the movement of these instruments were made by Elliot Brothers. It could be a tradition from the early days of electrical instrument making to produce scaleplates in this way by painting over a mirror finish brass plate. When electrical instruments stayed in laboratories, or if they were unfortunate, in workshops, damp was probably not considered a likley hazard.

I have a Model 4 (34 Ranges) 14-2098 which has a seperate mirror and an apparently aluminium scaleplate, so there seem to be some variation in what was used. It could be that this meter was repaired some time after manufacture and a new movement with separate scaleplate and mirror factory fitted. The owner would have been much more interested in functionality rather than historic accuracy at the time.

PMM
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Old 12th Dec 2018, 12:47 am   #16
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Default Re: Avo 36 range restoration

That's interesting for a start Peter, as my Model 4 is instrument No.2152 which helps pin it down to Jan-April 1934.

I don't have it to hand today so can't confirm whether the pin-punch cardinal marks are present.
What i would put forward, is that if you fit a newly scanned/printed scale plate which does not exactly match the scale-shape (arc) of your meter movement, the needle would not be parallel with the gradations...and would, to the human eye, appear bent. The eye picks this up very easily.

I was fortunate enough to introduce a scale plate from one Model D, to the movement of another Model D. They were perfect friends, but as Peter points out this is not a guaranteed success. Even Universal Avominors (Early '40's to late '50's) appear to have six different scale shapes- I did manage to assemble a Type E meter with an E6 movement to an E5 scale plate. The results were satisfactory. Luck played a part, no doubt.

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Old 12th Dec 2018, 1:04 am   #17
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Default Re: Avo 36 range restoration

So, do you think is better to change all the movement with the scale plate or just the scale plate? (in same model i mean)
 
Old 12th Dec 2018, 1:13 am   #18
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Default Re: Avo 36 range restoration

In your case Aitor i would say, try it and it might be okay. As you remove a scale-plate from a movement it is always easy to bend the needle and damage it, but as you have already been carefully dismantling these things i think you are aware of this and very cautious.

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Old 12th Dec 2018, 1:25 am   #19
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Default Re: Avo 36 range restoration

As you know, the movement for my AVO 7 was in very bad condition but the scale plate is quite good and with its serial number.

I tried to repair it, and it is working, but faulty. In a few days i will receive the new movement. Today it just arrives to my mother in law´s house in Malaga, because the seller did not send it to Canary Islands.

I am in two minds as to whether or not I should change the whole movement and loose the serial number or install the new movement with the original plate with my AVO serial number and perhaps as Thephilpott said have problems with the parallelism of the the needle and the gradations.


In my 36 range AVO, i think i do not have that problem (will see when receive it), buy¡t Superscope needs a new plate or an scanner. So it is interested what Thephilpott and Pmmunro said about the parellelism between the needle and gradations...

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Old 12th Dec 2018, 10:55 am   #20
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Default Re: Avo 36 range restoration

I wonder if the way forward with Damaged Scaleplates might be to obtain a Scan
and Edit out the Radial Lines using Photo Shop or similar, and re-draw them in,
like AVO themselves used to do after the new Print is attached.

One advantage would be, it would be calibrated (relatively speaking) to the
movement as it is today, correcting any aging or damage that the Movement has
suffered.
I think this is the approach I might try.

Aitor,

Don't worry about the Scan for me, I will scan the Scaleplate on my
earlier Model, as it is in Mint condition.
I was just holding out on opening it up, in case it got damaged in the process, but
needs must.
I'm not sure how a Scanner will react to that Mirrored Surface however.

Might need to be Photographed instead, but then setting up the Camera to avoid
parallax errors will be Fun.


Ian
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