AVO meter help required. - UK Vintage Radio Repair and Restoration Discussion Forum

paul1962 · 24th Oct 2021, 1:52 am

Hello everyone

Firstly, many thanks to those who are interested in my thread and taking the time to view it.
OK, here is the scenario ..
I have an AVOMeter Test Set No 1 (ex NATO equipment). I have replaced both batteries with new units, the voltages are seeming to work fine on ac, and I believe this to be the case on dc also (although, to be fair, the reading on a brand new D cell appears to be 1.3 rather than 1.5V, but possibly a slightly old stock battery)
The ohms settings can be zeroed on the high range and also the low range on the meter, BUT .. on the mid range ( ohms divided by 100 setting), I cant get this to go any lower than 100 on the meter, even with the adjustor at full tilt. It was originally sitting at 500, but I removed the main workings and cleaned up the contacts as best as I could, which has resulted in the last 100 readings now.
So, I guess my question is why is this ahppening and how do I correct it ? Is this a known issue with these AVO's ? I know they are high sensitivity models, but being ex NATO spec (with potted components etc) I would assume that these would be catered stronger for harsher environments etc.
Over to you in the know and all input greatfully received.
Many Thanks in advance.

Refugee · 24th Oct 2021, 2:47 am

The divide by 100 range only works with a brand new D cell.
1.3 volts will not be enough and you will never get it to zero.

Phil G4SPZ · 24th Oct 2021, 8:34 am

Yes, pristine-clean contacts and a fresh D cell are absolutely essential.

paul1962 · 24th Oct 2021, 2:16 pm

Thanks for your input so far guys

I guess it's off to get some more batteries that are better than these damn Duracells

Any recommendation as to a good reliable battery these days ? (I have no doubt that they are all made in China and rebranded), but maybe there is something decent that won't throw its content all over the battery compartment

Phil G4SPZ · 24th Oct 2021, 2:18 pm

I order all my batteries online from CPC Farnell. They don’t leak, in my experience, but any cell left for years in a discharged state is likely to cause trouble.

paul1962 · 24th Oct 2021, 2:23 pm

Hello Phil,
I have just checked for a D Cell on their site and the only one they seem to list is rated at 1.2V and 4AH.
This puts them at about the same range as the Duracells I have

Refugee · 24th Oct 2021, 3:07 pm

My AVOs work fine with Aldi batteries and 5 CR2032 cells and a spacer for the high range.

Superscope · 24th Oct 2021, 3:08 pm

Hi Paul,

If it is 1.2 V and 4 Ah it is clearly a rechargable D type you are looking at.

These are not suitable for Avo meters.
You really need 1.5 Volts or very close too it.

Get yourself down to B&Q or Screwfix and buy some Varta D Types.
As far as I know, they are still made in Germany.

The Battery you measured at 1.3v, if it was a regular Battery and not a
rechargable, it is as good as completely Dead.
Assuming of course you measured it with a known good Voltmeter, and not
a currently suspect Avo meter.

A fresh primary D Battery should read around 1.6 Volts.

Ian

The Philpott · 24th Oct 2021, 6:32 pm

New alkaline D cell (or even a zinc chloride will do)
Anything but a duracell.
Dave

mark_in_manc · 24th Oct 2021, 9:28 pm

(I opened an AVO8 mk5 this afternoon, and found a nice blue Ever Ready SP2! No trace of a leak...or any current

)

24th Oct 2021, 1:52 am	#1
paul1962 Pentode Join Date: Jun 2020 Location: Woking, Surrey, UK. Posts: 146	AVO meter help required. Hello everyone Firstly, many thanks to those who are interested in my thread and taking the time to view it. OK, here is the scenario .. I have an AVOMeter Test Set No 1 (ex NATO equipment). I have replaced both batteries with new units, the voltages are seeming to work fine on ac, and I believe this to be the case on dc also (although, to be fair, the reading on a brand new D cell appears to be 1.3 rather than 1.5V, but possibly a slightly old stock battery) The ohms settings can be zeroed on the high range and also the low range on the meter, BUT .. on the mid range ( ohms divided by 100 setting), I cant get this to go any lower than 100 on the meter, even with the adjustor at full tilt. It was originally sitting at 500, but I removed the main workings and cleaned up the contacts as best as I could, which has resulted in the last 100 readings now. So, I guess my question is why is this ahppening and how do I correct it ? Is this a known issue with these AVO's ? I know they are high sensitivity models, but being ex NATO spec (with potted components etc) I would assume that these would be catered stronger for harsher environments etc. Over to you in the know and all input greatfully received. Many Thanks in advance.

24th Oct 2021, 2:47 am	#2
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Avo meter help required The divide by 100 range only works with a brand new D cell. 1.3 volts will not be enough and you will never get it to zero.

24th Oct 2021, 8:34 am	#3
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: Avo meter help required Yes, pristine-clean contacts and a fresh D cell are absolutely essential. __________________ Phil Optimist [n]: One who is not in possession of the full facts

24th Oct 2021, 2:16 pm	#4
paul1962 Pentode Join Date: Jun 2020 Location: Woking, Surrey, UK. Posts: 146	Re: AVO meter help required. Thanks for your input so far guys I guess it's off to get some more batteries that are better than these damn Duracells Any recommendation as to a good reliable battery these days ? (I have no doubt that they are all made in China and rebranded), but maybe there is something decent that won't throw its content all over the battery compartment

24th Oct 2021, 2:18 pm	#5
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: AVO meter help required. I order all my batteries online from CPC Farnell. They don’t leak, in my experience, but any cell left for years in a discharged state is likely to cause trouble. __________________ Phil Optimist [n]: One who is not in possession of the full facts

24th Oct 2021, 2:23 pm	#6
paul1962 Pentode Join Date: Jun 2020 Location: Woking, Surrey, UK. Posts: 146	Re: AVO meter help required. Hello Phil, I have just checked for a D Cell on their site and the only one they seem to list is rated at 1.2V and 4AH. This puts them at about the same range as the Duracells I have

24th Oct 2021, 3:07 pm	#7
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: AVO meter help required. My AVOs work fine with Aldi batteries and 5 CR2032 cells and a spacer for the high range.

24th Oct 2021, 3:08 pm	#8
Superscope Octode Join Date: May 2017 Location: St Austell, Cornwall, UK. Posts: 1,018	Re: AVO meter help required. Hi Paul, If it is 1.2 V and 4 Ah it is clearly a rechargable D type you are looking at. These are not suitable for Avo meters. You really need 1.5 Volts or very close too it. Get yourself down to B&Q or Screwfix and buy some Varta D Types. As far as I know, they are still made in Germany. The Battery you measured at 1.3v, if it was a regular Battery and not a rechargable, it is as good as completely Dead. Assuming of course you measured it with a known good Voltmeter, and not a currently suspect Avo meter. A fresh primary D Battery should read around 1.6 Volts. Ian

24th Oct 2021, 6:32 pm	#9
The Philpott Dekatron Join Date: Aug 2016 Location: Colchester, Essex, UK. Posts: 4,106	Re: AVO meter help required. New alkaline D cell (or even a zinc chloride will do) Anything but a duracell. Dave

24th Oct 2021, 9:28 pm	#10
mark_in_manc Octode Join Date: Nov 2011 Location: Manchester, UK. Posts: 1,874	Re: AVO meter help required. (I opened an AVO8 mk5 this afternoon, and found a nice blue Ever Ready SP2! No trace of a leak...or any current ) __________________ "The best dBs, come in 3s" - Woody Brown