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Avo Eight.

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Active Member

The resistance battery in my Avo has gone flat.

I think i left it unattended with the leads touching,
on resistance.

The battery has gone flat.
Its been low for a while,
now its un-useable.

Any suggestions ?

OK, I give up. I'm assuming AVO means the same thing VOM means. What the heck is the "eight" about? Oh - replace the battery or recharge it. I'll bet you knew that. What's up?
Hi Ron,

No, Avo doesn't mean VOM, i don't know what VOM means.
I have attached a little info about Avo meters,
which are well known in the trade.
(or so i thought)

These jerks think i'm happy to pay over ten pounds
sterling for a little 15v battery, they have another
think coming.
Ive been looking at little 12v batteries that are
available for £1-79p each from
But i don't know if i can alter the innards to use it.

Also i might see if i can put a 'time-out' on the
battery function somehow.

Surely someone has dealt with the 'Avo battery'
problem before now ??

John :)


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I thought maybe AVO meant Amps-Volts-Ohms (I still do). VOM means Volt-Ohm-Milliammeter.
I found a picture of an AVO 8. It may be more popular on your side of the Atlantic. What trade are you in? What are the advantages of an analog meter over digital? It certainly isn't price!
I don't have a solution for the battery problem. I do know my Fluke DMM (digital multimeter) goes off by itself after about 10 minutes of inactivity.
Hi Ron,

The older digital meters were good for working in dim or gloomy
conditions, but i haven't seen an LED one now for years.

Yes, they called their range Avo after 'Amps-Volts-Ohms' which
are its functions. (least, thats my understanding of it too)

Don't think theres any advantages of analogue over digital in
normal use, except two very minor points. One, the analogue
uses what its measuring to produce the reading and needs no
batteries - except for the ohms functions. Two, the analogue
meter can be used in areas where electrical disturbances may
damage electronic circuitry. Such as arc welding, or static
build up. Not really very meaningful circumstances.

You say 'over your side of the Atlantic' so i am going to
guess that you noticed the £-sign, and correctly assumed i am
in England.

So i am going to guess that you are in one of the countries on
the other side of the Atlantic. The other side from me that is.
Canada, Mexico, USA, Caribbean, Greenland, Brazil, Alaska, Peru,

And many others i don't recall, but i will guess at USA.

About the battery, i was thinking, if i get one of those LEDs
that flash on and off, then i could mount it so that it shows,
and when the battery is in use it would flash.
Yes, i know it would use more current driving an LED as well,
but it would be harder to forget, and leave it on.
Thats what kills the battery.

What do you think ?

John :)
Looking through google's 'images' under Avo,
i found this pic,
so it looks like one of their newer models
actually does have LEDs.

I thought all the new ones were LCDs,
obviously not.



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Just a bit of further information about the AVO8. This was the company's penultimate meter prior to the introduction of digital multimeters (their last was the AVO9). Their range of instruments was the trade standard for electrics, radio, and television up to the coming of the digital meter. They were extremely robust, accurate, and highly prized in any workshop. They were bench instruments but AVO also did a pocket version - the AVO Multiminor.

The company that made it was originally known as ACWEECO. It stood for Automatic Coil Winding and Electrical Equipment COmpany. It started life making coil winding equipment - a major business in those days because almost all RF coils had to be wave-wound in Litz wire.

It progressed to discrete voltage and current meters, a 500V isulation tester known as the 'Megger', and valve testers. When they made their first multipurpose analogue meter, they coined the word AVO to represent its functions.

I hope someone may find that of interest.
john1 said:
........Also i might see if i can put a 'time-out' on the
battery function somehow....
You don't need a time-out on the battery - current is only drawn from it when on the OHMs range and the test leads are connected to a resistor, ie. when the meter is indicating.
Hi pebe,

Yes, i realise that, however as almost any analogue meter user
can tell you, the leads have a life of their own.
They don't have much to do for most of the time, and when the
user gives them a battery to cheer them up, they seem to get
uncontrollably drawn together. They also get devious and sneaky
they don't engage themselves whilst you might notice, they will
wait until you're finished using the meter for the time being,
then they will cheekily couple up as you switch off the soldering
iron. Like clandestine lovers, they optimise their opportunities
and like thieves in the night they will consume the meagre
resources until the supply is exhausted.

This is not the first time that my ohms testing has left me with
a dead battery, nor will it be the last, unless i do something
about it.

It's easy to say - don't leave it on OHMS, but its not so easy
to do.

I would be interested to hear from anyone else here who has found
their ohms battery flat when trying to use it !!
Surely its not just me ??

I have found a flashing LED in my collection, but i dunno if
thats the way i want to go yet ...

Regards, John :)
How about adding a power MOSFET (milliohms on resistance) in series with the battery, and controlling it with a CMOS 555 timer triggered by a pushbutton switch? You could design it to time out after 15 minutes or so.
I once made a timer for a SMT soldering iron that was always getting left on and burning up the tips. I used a wind-up, 1 hour max timer like you see for bathroom ceiling heaters in hotels, but it's the same principle - just radically different hardware. :D
I picked up my old AVO 8 (panclimatic) a little over five years ago at auction, paid a fiver and it came with battered carry case.It also came with a flat 15v battery, so I began my quest for a replacement.
Most said "Sorry mate can't help" , one even started laughing and others just start rubbing thier hands together, drooling at the prospect of a desparate buyer.
Now days it lives in the workshop tetherd by flying leads to the bench supply.

Yes a timeout system is certainly one possibility.

Another possibility is a flashing LED.

Another possibility is a 'test' button mounted on the front
somewhere, the logic here being that the button has to be
pressed to complete the circuit to test ohms. Fairly simple,
and should be easy to do.

Another possibility is a beep. I was thinking that as there
are two batteries in the battery compartment, one hard to get,
and one easy to get, and there is a little room in there.
Maybe i could make a little beeping noise from the larger
single cell with one of those tiny noise makers, and trigger
it whenever current is drawn from the small expensive 15 volt
battery. That would need no external alterations to the unit
like LEDs or buttons.

Another possibility, but not an answer, is to use the little
12 volt batteries that cost £1:79p, and try not to cry too
much when it goes flat. The disadvantage here is that 12 volts
is right at the MAX on the adjuster pot. Now, i have yet to see
a diagram of the Avo, so i am not sure if i can ALTER something
(shudder) to make it have at least some adjustment using a
12 volt battery. This so far is my favourite option.

Any suggestions, no matter how bizarre, will be welcomed and
treated with the absolute minimum of confidentiality.

As you probably know, the little 15v battery is only for the
higher ohms range, the other easy to get battery is for the
lower ohms range.
I had a reply from 'The Small Battery Company' they sent me
this in an e-mail:

It looks like a direct replacement, but i have yet to check
the length, but it looks close enough to me.

I still think thats too much though, (money)
but you might be quite happy with it.
If i can get it to give a bit of adjustment using 12v,
then thats what i will do.

Regards, John :)
i found this diagram.
**broken link removed**
i'm not finding it easy to follow.

but i will persevere.

John :)
Yes i'm still staring at this diagram,
with a very gormless look on my face.

One thing i have figured out,
those rectifiers in odd places here and there,
aren't rectifiers at all.

They are cam driven contacts.
At least i think they are ...

Anyone who could 'simplify' the resistance set
up would be welcome.

John :)

i had a look around on that 'richardsradio' page, and i found this:
**broken link removed**

Here he descibes how he dealt with the Avo battery problem.
With pictures.
He says put two PP3 batteries and a 3.3k in series.
He says it fits in the battery clip ok too.

This seems so simple, i may go for this solution.

John :)
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