Documenting Avo Design

[AndyGilham]

As many of you know, I work for Megger (Formerly Avo) and have taken an avid interest in the companies history. Because of this, I have gained a lot of information about the company, and more importantly its research, development and manufacturing processes.

Just to give everyone an idea of what i am doing with the documentation, I have attached a report on the Admiralty Pattern 48A Double Range Transformer that I have wrote (A nice simple one to start with)

My on going intention is to continue generating these sort of documents over time.

Feedback would be nice (including bad grammar and spelling.... )

Andy

[Electronpusher0]

This is a very detailed and valuable document, I am impressed.
Just one suggestion, it would be great if you could also include a photo of the final article.

Regards
Peter

Very good job, very interesting to know the different materials used during the time.

Congratulations!! Hope to see another report soon!

A photo of the real device will be nice at the end.

[Sinewave]

Very interesting and in fact have one here in a box. A little marking on the plate, but otherwise it's all here. I have around three of these for a model 40 and two for a model 7.

[M0FYA Andy]

An excellent report!

[Dekatron]

Wonderful!

Let me know if you ever have a go at the valve testers!

/Martin

[Skywave]

Originally Posted by AndyGilham

My on going intention is to continue generating these sort of documents over time.
Feedback would be nice (including bad grammar and spelling.... )
Andy

I would just like to say - without any intention whatsoever of sounding patronising - that I consider what you are doing - and intend to continue doing - to be a worthwhile contribution to the preservation of vintage electronics technology.
So well done - and thank you.

Al.

[AndyGilham]

Thank you for the positive feedback on the report. It makes for an interesting job, just looking at each document and then considering those individal changes and how they relate to the design.

Andy

[kalee20]

A good report - thank you!

Comments -

1) Needs page numbers (helps with describing suggested corrections!)

2) Third page: windings are (?) both secondaries, not primary and secondary. The primary is the single turn thick copper strip.

3) I looked at the turns count, and it would seem that the two windings are connected together for the 200A : 100mA range (ie (488+1485) : 1, being not quite 2000:1 to compensate for magnetising current error. So it would seem that the windings are interconnected internally to give, via the two sets of terminals, 488 : 1 or 1973 : 1. May be worth mentioning this?

4) The label photos page 6: may be worth highlighting that they are strictly incorrect, stating 'USE 100MA RANGE' and 'USE 120MA RANGE' as capital m has never (as far as I know) meant 'milli'. Interesting that the label page 5 is correct, and the mixed case text does not look 'wrong'! Your own text is of course correct!

5) Typos/minor niceties, as requested: Page 3 add the word 'turns' after 1470. Delete the dot in 33.SWG, so consistent with 40 SWG. Add " (inch) to the 1-1/2" lead wire length.

Looking forward to the All-Wave Oscillator next!

[AndyGilham]

Kalee,
Thank you for the feedback
1. I will add the page numbers, good point.

2. The references i used are based on the drawings themselves, so the Primary coil is what its called on the drawing 'Primary'. The Wound coil (a seperate drawing) details a Primary Winding (488 turns) and a Secondary Winding (1485 Turns). I guess this wound former is also used on another product, hence the reference to both Primary and Secondary. But i see what you mean.

3. I have attached the section of drawing that details the windings. There is no reference to internal connections, simply 2 windings interleved with paper with start and finish leadouts. I checked the assembly drawing and there is no link between the leadouts there either. YOu may well be right, but it is certainly not detailed.

4. Yes it felt wrong typing MA, although seems to be a common sight on some of these old documents. I will make a mention to it.

5. I shall sort my typos!

Thank you
Andy

[AndyGilham]

Originally Posted by Sinewave

Very interesting and in fact have one here in a box. A little marking on the plate, but otherwise it's all here. I have around three of these for a model 40 and two for a model 7.

Nice to see more photos of the transformer. Yours has the older namplate on top, so pre October 1960 (Different pitch rivet holes and text).
Whereas the one shown on my friend Ricahrds site
(http://www.richardsradios.co.uk/avomodel48A.html) shows the post 1960 variant.

The other difference i have seen is the battleship grey painting. My documentation details that the braszed joint between Primary coil and mounted blocks is battleship grey, but looking at your images and Richards, only the Washer and Wingnuts are battleship grey. However, a forum member here did upload photos of this transformer with the brazed joint and block painted, but not the washer and wingnuts! Seems to be some disparity there!

Andy

[Sinewave]

Thanks Andy,

Here's some of the transformer for the 7.

And a document number in the header on each page, it was easy when documents where paper, not so now.

[kalee20]

Originally Posted by AndyGilham

The references i used are based on the drawings themselves, so the Primary coil is what its called on the drawing 'Primary'. The Wound coil (a seperate drawing) details a Primary Winding (488 turns) and a Secondary Winding (1485 Turns). I guess this wound former is also used on another product, hence the reference to both Primary and Secondary. But i see what you mean...

There is no reference to internal connections, simply 2 windings interleved with paper with start and finish leadouts. I checked the assembly drawing and there is no link between the leadouts there either. You may well be right, but it is certainly not detailed.

Interesting - the 'primary' and 'secondary' designations came from ACWEECO themselves!

I'm thinking , as for internal connections, 50A in will give ideally 50/488A = 102mA out, using the 488 turn winding - which matches the 100mA output terminals. The extra 2mA is no doubt absorbed internally as magnetising current and core losses.

Similarly, 200A in 1973 turns (488+1485) gives 101mA, again matching 200A to 100mA instrument range with a bit of correction for magnetisation and losses. But 200A in 1485 would give 134.6mA and that's wildly out for 100mA. So the windings MUST have been seriesed-up for 200A measurement.

[The Philpott]

I have early and late transformers so can confirm any external differences in due course.
The most obvious one is the lack of nickel plating on the WW2 ones, also the wingnuts are not as neatly made. Adequate, just not very smart. Well done on the document/s Andy.

Dave

[AndyGilham]

The wing nuts are one thing I had no details off, I have the ACWEECO part number, but. was not in the drawing set I have.

Interestingly I stumbled across another 'primary' winding, that was dimensionally the same in its formed position, so it must be used on a similar transformer assembly. However, it was twice as tall, and included a large raduis on the end faces. I guess it was larger to accommodate an increased current capacity.

Andy

[David Simpson]

What Andy is doing is a great boon to the vintage radio fraternity. Hopefully his research & documentation will go from strength to strength.
Me, I'm just an old analogue guy with limited computing & software skills & have come to terms with that. However, for some years now, since joining the Forum, I have come to realise that there is an amazing wealth of Forum membership based experienced info on, - say for example - AVO 8 MM's & VCM's, enough I reckon to produce a definitive book or modern manual on these items of test equipment. Likewise for Mullard HSVT's, HP's range of scopes, and so on. So - are there any ex HP & Mullard, Marconi, TEK, etc. technical employees out there with similar skills & drive as Andy ?

Regards, David

[AndyGilham]

The challenge i have is really knowing what to do next.....work on, for example an entire instrument, like a Model 8 (mark 1), or concentrate on the differences between models of particualr parts......!

Andy

[Dekatron]

Asking Megger to put as much of the old drawings and other stuff in the public domain for free download would be a good starting point! 😊

Anything at all that add to the information we have is good, but I myself find that projects close to my heart comes out the best. Requests are sometimes hard to handle as the person requesting the information might have another idea on what they want than you yourself.

[David Simpson]

Andy, going by the massive AVO Multimeter Survey thread, other folks experiences & collections, and my own experiences of, at times over the years, repairing/servicing, and owning one or more of each of the AVO8 MM Marks from 1 to 7 - perhaps you might consider a technical history of this most popular range, for a start. What was their production lifespan - what - 1950's to the 1980's ? All with a 50uA fsd meter movement, originally a quadrant display, then latterly a kidney profile display, 20Kohms/V,and so on.
Some AVO7 buffs might not agree, but it might prove a much harder task if you were to include 7's, 40's, 9's, etc.

Regards, David