If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ash Small wrote ...
Well, I've some spare cash now, and before deciding on which magnets to order, thought I'd do a bit of research.
While I've seen the arm that you mention on meters before, I can't find any mention of it in any of the articles I've looked at.
Patrick wrote ...
. remember the d'Araonsval meter has that arm stretching in a curve across from pol to pole, to linearize the meters scale, otherwise what your showing above is exponetial or logarithmic, i forget which.
im trying to find pics and my book at the moment... to show what i mean.
i may not have said this all quite right let me get another post to you regarding this matter.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
I scored this for a tenner on Ebay last night, and collected it this morning. It was two miles away.
AVO Model 8 Mk III
I'll open it up and have a look at the movement later. I'm particularly interested in looking at the 'concentrator'.
It's giving some strange readings on the Ohm scale, but I'll try some new batteries and see if that sorts it out.
Coo, that's a real beauty, Ash, and well cared-for by the looks of it.
You should put a fresh 15V battery in it, before drawing any conclusions about the resistance ranges.
All being well with the new battery, I would resist the temptation to open it and look inside. It has survived all those years without your intervention!
Registered Member #1334
Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615
Ash Small wrote ...
I scored this for a tenner on Ebay last night, and collected it this morning. It was two miles away.
AVO Model 8 Mk III
I'll open it up and have a look at the movement later. I'm particularly interested in looking at the 'concentrator'.
It's giving some strange readings on the Ohm scale, but I'll try some new batteries and see if that sorts it out.
Congratulations. Seconded to what PM said (don't mess too much with it - they are subtle and quick to anger). I don't know why but I've fallen in love with AVOs recently. Got one at a boot fair in Tunbridge Wells about a month ago for 13 quid complete with pristine leather case (Its a Model 47 or a Model 40, not sure!). Leads a bit crummy, but otherwise OK. Seems mostly ok - movement has been replaced. Now got 4 of them!
The place to go for info on AVOs and how to look after/repair them is the UK Vintage Radio Repair and Restoration Discussion Forum on "Specific Vintage Equipment" .
They've been extremely helpful with my questions and also maintain a register of 1000's of these things' serial numbers. They will also tell you when yours was made.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
Coo, that's a real beauty, Ash, and well cared-for by the looks of it.
You should put a fresh 15V battery in it, before drawing any conclusions about the resistance ranges.
All being well with the new battery, I would resist the temptation to open it and look inside. It has survived all those years without your intervention!
This one has been converted to take an A23 12V battery in series with an AAA 1.5V battery. This gives 13.5V (according to my limited maths)
Is this sufficient, or should I add another AAA to bring it up to 15V?
Also, the battery cover is missing, but I'll make up an aluminium one, I think. (If it works OK once I've replaced the batteries.
Maybe you are right, opening it up could be considered as 'cheating', but I've not been able to find any detail about the iron magnetic field concentrator online. (Some articles refer to an iron core or a piece of iron tubing inside the coil)
I downloaded the AVO service manual, and that seems to state that the concentrator remains in the scaleplate assembly when the coil is removed.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
Proud Mary wrote ...
Coo, that's a real beauty, Ash, and well cared-for by the looks of it.
You should put a fresh 15V battery in it, before drawing any conclusions about the resistance ranges.
All being well with the new battery, I would resist the temptation to open it and look inside. It has survived all those years without your intervention!
This one has been converted to take an A23 12V battery in series with an AAA 1.5V battery. This gives 13.5V (according to my limited maths)
Is this sufficient, or should I add another AAA to bring it up to 15V?
Also, the battery cover is missing, but I'll make up an aluminium one, I think. (If it works OK once I've replaced the batteries.
Maybe you are right, opening it up could be considered as 'cheating', but I've not been able to find any detail about the iron magnetic field concentrator online. (Some articles refer to a piece of iron tubing inside the coil)
I downloaded the AVO service manual, and that seems to state that the concentrator remains in the faceplate assembly when the coil is removed.
Oh dearie me - we can only hope that the person responsible for such an awful bodge job on the batteries hasn't been tinkering elsewhere.
In the normal course of events, one can compensate for declining battery voltage by means of set zero, but I would advise you to use the full 15 V for re-commissioning so you can test the set zero across its whole range, and perhaps identify any tinkering or other short-coming.
It is often possible to identify past bodging and tinkering by examining the fastenings with a jeweller's loup, as the bodger will commonly use screwdrivers or sockets of the wrong size, which leave their own characteristic markings behind them.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
As Small' It's amazing how many seemingly unimportant details turn out to be very clever bits of engineering - often too late to be fully appreciated. (oops !)
If in good condition it's a useful meter
if minor repairs (resistors etc.) can get it to a useful state then it would be a nice little project.
If there is bad corrosion or the meter movement (magnet, pivots, coil, springs, pointer et.) needs repair then it can be a significant project, hours of restoration calibrated vs. a $5 dmm. (that I've previously tested the calibration of common ranges to better than 1%)
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
. In the normal course of events, one can compensate for declining battery voltage by means of set zero, but I would advise you to use the full 15 V for re-commissioning so you can test the set zero across its whole range, and perhaps identify any tinkering or other short-coming.
It is often possible to identify past bodging and tinkering by examining the fastenings with a jeweller's loup, as the bodger will commonly use screwdrivers or sockets of the wrong size, which leave their own characteristic markings behind them.
Well, I've taken a couple of A23's apart and made one 10 cell battery (reads 15.6V on my DMM). I can't get it to zero on the Ohms/100 range(lowest it will go is 50 (equal to 0.5V), so I assume it was adjusted inside to allow zeroing on the 13.5V it was operating on before.
I found the instructions to adjust this earlier, but can't seem to find them now.(I'm sure I will if I keep looking) but this means I'll have to open it up anyway. (The internal adjustment should be set so that the external adjusters are midway when it is zeroed, to allow for adjustment in either direction)
I was on the UK Vintage Radio Repair and Restoration Discussion Forum earlier, but I'm not sure if it was there or somewhere else.
EDIT: The 15V battery is only used by the Ohms X 100 range (according to the circuit diagram), so the above fault isn't due to the 15V battery
EDIT EDIT: It's a resistance problem. I shorted the terminals using some silver plated wire and it zeros. I'll try cleaning the terminals, that should improve things further. Time for some new leads I think.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
Does it display believable readings in voltmeter mode?
When connected to a 12V battery charger with a 21 watt bulb as ballast, it reads 8.5V, my DMM reads 9.17 (there could be a voltage drop due to high resistance in the terminals)
The same circuit gives 1.2 amps on both the AVO and DMM.
I'll set up a better test with a car battery in the morning.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
Moving Coil Meter
