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Old 27th Nov 2021, 5:38 pm   #1
GB52RAD
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Default Heavy Duty AVO British Railways.

Hi everyone. I'll start by apologising as I am sure this is a really old chestnut.
I bought what I believe to be a Mk5 heavy duty AVO (British Railways version) off you know where and it is "as dead as a nit".
When I got it the cut out had activated and I reset it but no dice on any of the ranges, not least Ohms and low voltage DC.
I have examined it carefully and can find no obvious mechanical damage or burn marks, indeed it seems in really good order. I have buzzed out the connections as far as I can work them out and have found no faults; the movement responds nicely + and - with a low voltage stimulation.

So I would like to try and find circuit/layout/component ident information to enable further investigation.
This is where the problems start as I know that information on this model is sparse and the only cct diagram I can find is frustratingly blurred.
Given the construction is complicated and there are a lot of fine wires involved I am reluctant to dismantle it yet.

Please can anybody point me in a useful information gathering direction?
Many thanks
GB.
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Old 27th Nov 2021, 11:29 pm   #2
JonSnell
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Default Re: Heavy Duty AVO British Railways.

This might help;
https://elektrotanya.com/avo_avomete.../download.html
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Old 28th Nov 2021, 12:09 am   #3
Techman
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Default Re: Heavy Duty AVO British Railways.

Quote:
Originally Posted by JonSnell View Post
This might help
Actually it won't, John

These are a bit of a 'special' and nothing like anything else and are a bit rare, I think.

It would have been helpful to members if the OP had included a picture, but he probably thought members would be familiar with what a "heavy duty" was.

I got one with my recent acquisition of old test gear etc. I'll post some pictures of it below to jog peoples memory, but I don't think there's much, if any service information on them out there...
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Old 28th Nov 2021, 12:18 am   #4
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Default Re: Heavy Duty AVO British Railways.

Quote:
Originally Posted by Techman View Post
I don't think there's much, if any service information on them out there...
Actually I'm wrong!

Just looked in the AVO file and I've got it...
HDmk5.pdf

Edit to say - this could be what the OP was saying about being a bit blurred, but I'm afraid that's the best there is.
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Old 28th Nov 2021, 9:20 am   #5
pmmunro
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Default Re: Heavy Duty AVO British Railways.

GB,

Your version of the Heavy Duty Avometer is the Railway Signalling variant which has different ranges to the commercial version, as in the attached table.

Also attached is a circuit diagram which I drew out for the standard HD meter. (My copyright, may be used freely, with acknowledgement, for non-commercial purposes).

It's a fairly simple meter so it should not be very difficult to work out the component values which apply to the Railway Signalling version.

There is a MOD Technical Handbook (Telecommunications W124, June 1962) which together with W121 & W122 gives fairly full information on the standard version but it is classified "Restricted" so I don't know what its publication status is. It would certainly give you most of the information you would want and is very probably based on information which was freely available at the time.

PMM
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File Type: doc HD Circuit Diagram.doc (196.5 KB, 59 views)
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Old 28th Nov 2021, 9:22 am   #6
pmmunro
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Default Re: Heavy Duty AVO British Railways.

GB,

I've just looked more closely at your photograph and your's seems to be the commercial version which has found itself a Railway Signalling leather case.

PMM
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Old 28th Nov 2021, 11:15 am   #7
GB52RAD
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Default Re: Heavy Duty AVO British Railways.

Thanks to all who have replied. I’ll see what I can sift out and try and make progress. Hopefully these photos have uploaded. It my first attempt!
Thanks again. I’ll post my progress.
GB.
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Old 28th Nov 2021, 1:58 pm   #8
GB52RAD
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Default Re: Heavy Duty AVO British Railways.

Photos I had intended.
Regards and thanks for any more advice.
GB.
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Old 28th Nov 2021, 4:47 pm   #9
GB52RAD
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Default Re: Heavy Duty AVO British Railways.

Well thanks to all who have kindly responded especially pmmunro. The cct diagram you have supplied is very clear.
I think there was a bit of confusion out there as the photos earlier referred to were not from me. My machine does not have the top central adjustment control. It does however have a really good original case so whoever guessed that was spot on!��
I’ll see if I can locate the resistor position and buzz out a line to the movement.
It was only £16 so a bargain worth resurrecting. The seller told me it had lain in his dad’s cupboard for 50yrs and as I can see a pencilled date of 1967, I’m assuming it dates to that period.
Thanks again. Graham.
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Old 28th Nov 2021, 8:37 pm   #10
majoconz
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Default Re: Heavy Duty AVO British Railways.

An apprentice in our lab spent two days fault-finding an AVO 8 - eventually it dawned on him that the red lead was open circuit!
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Old 28th Nov 2021, 11:24 pm   #11
pmmunro
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Default Re: Heavy Duty AVO British Railways.

GB,

Your neter's serial number ends "263" indicating it was made in February 1963.

PMM
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Old 29th Nov 2021, 5:44 pm   #12
GB52RAD
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Default Re: Heavy Duty AVO British Railways.

Quote:
Originally Posted by pmmunro View Post
GB,

Your neter's serial number ends "263" indicating it was made in February 1963.

PMM
Thanks again Pmm. I’ll get back to it next weekend and see if I can find the o/c.
Cheers
GB.
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Old 3rd Dec 2021, 7:26 pm   #13
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Default Re: Heavy Duty AVO British Railways.

I well remember these being used by signalling technicians before digital meters arrived. Railway signalling power supplies are/were mainly 24 and 50Vdc and 110Vac. There is also a lineside 660Vac signalling supply that is stepped down to 110Vac for lineside equipment cabinets.

I recall seeing an Avo 8 Mk 3, that was engraved BR-WR S&T Dept.
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