UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Test Gear and Workshop Equipment

Notices

Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

Closed Thread
 
Thread Tools
Old 8th Feb 2016, 3:00 pm   #1
mikeald
Retired Dormant Member
 
Join Date: Aug 2011
Location: Cardiff, Wales, UK.
Posts: 97
Default AVO 8 Mk 5

Hi all,

I have just aquired an AVO 8 mk5 in excellent cosmetic condition.

I have not used one of these before.

Is this a 'good' meter purely for measuring DV voltages in radios?

Is there anything I need to do to calibrate the meter etc As at the moment I have noticed that when I measure DC voltages, the needle never quite goes back to the 0 position.

I have also noticed that the meter requires a 15 volt battery, I was wondering if this is required for reading low dc voltages, I am assuming not, as it seems to be working now?

Thank you

Last edited by mikeald; 8th Feb 2016 at 3:05 pm.
mikeald is offline  
Old 8th Feb 2016, 3:14 pm   #2
Nicklyons2
Octode
 
Nicklyons2's Avatar
 
Join Date: Jan 2013
Location: Barnsley, South Yorkshire, UK.
Posts: 1,517
Default Re: avo 8 mk 5

The batteries are needed only for the OHMS ranges; the 'D' cell for low resistance ranges, the 15v battery for the higher resistance ranges. There is a meter 'ZERO' set screw more or less dead centre on the front - only adjust GENTLY and with care (like 10 degrees at a time) never go more that 90 degrees either way. The meter is calibrated to be read horizontally. DON'T recalibrate it to read 'stood-up'.

If the amount it's out is only something like the width of the pointer I'd leave it alone.
Nicklyons2 is offline  
Old 8th Feb 2016, 3:24 pm   #3
mikeald
Retired Dormant Member
 
Join Date: Aug 2011
Location: Cardiff, Wales, UK.
Posts: 97
Default Re: avo 8 mk 5

lovely ok thank you.

One more thing - What sort of reading can I expect on this compared to a digital meter?

I.E if I am reading 13 volts on a digital meter, would I also expect 13v on the AVO? Or would it be more or less?

Cheers
mikeald is offline  
Old 8th Feb 2016, 3:45 pm   #4
Nicklyons2
Octode
 
Nicklyons2's Avatar
 
Join Date: Jan 2013
Location: Barnsley, South Yorkshire, UK.
Posts: 1,517
Default Re: avo 8 mk 5

For resonably low source resistances, such as those found in transistor circuits and the power stages in valve equipment, they will both read the same (within the limits of accuracy). The differences will occur with high resistance/impedance parts of the circuit when the AVO will 'load' the circuit and affect the voltage. In DC terms if you're measuring with components 100K Ohm or less I wouldn't worry.

Further for a.c. waveforms both meters (unless your digi one is V. expensive) will assume sine wave; any other wave shape is a bit meaningless. The AVO will be OK with sine waves up to a few hundred Hz (though cal is for 50/60 Hz) the digi will probably cope up to a few KHz or so.

Having said that, for low frequency waveshapes other than sine, the AVO will probably make a better 'stab' at it.
Nicklyons2 is offline  
Old 8th Feb 2016, 3:49 pm   #5
Mooly
Octode
 
Join Date: May 2011
Location: Lancashire, UK.
Posts: 1,349
Default Re: avo 8 mk 5

This shows my AVO 8 mk5 calibration as compared to two digital meters.
Attached Files
File Type: pdf AVO Calibration.pdf (34.7 KB, 276 views)
Mooly is offline  
Old 8th Feb 2016, 3:56 pm   #6
mikeald
Retired Dormant Member
 
Join Date: Aug 2011
Location: Cardiff, Wales, UK.
Posts: 97
Default Re: avo 8 mk 5

THank you.

One thing I have just noticed is that the meter only works correctly when I push down on the x10k potentiometer... So something isnt right!
mikeald is offline  
Old 8th Feb 2016, 4:19 pm   #7
Thyristor
Pentode
 
Join Date: May 2015
Location: Hove, East Sussex.
Posts: 147
Default Re: avo 8 mk 5

Quote:
Originally Posted by Mooly View Post
This shows my AVO 8 mk5 calibration as compared to two digital meters.
Which DVMs did you use, Mooly, just out of interest. *

*Sorry, the anorak in me hates un-named equipment being cited !
Thyristor is offline  
Old 8th Feb 2016, 4:43 pm   #8
ted_ntsx
Pentode
 
ted_ntsx's Avatar
 
Join Date: Jul 2008
Location: Winterton-on-sea, Great Yarmouth, Norfolk, UK.
Posts: 137
Default Re: avo 8 mk 5

Quote:
Originally Posted by mikeald View Post
I have also noticed that the meter requires a 15 volt battery, I was wondering if this is required for reading low dc voltages, I am assuming not, as it seems to be working now?
I use two PP3's in my old Avo 8 in place of the defunct 15V battery.. There is just enough room in the case, and the few extra volts do not make any real difference.
ted_ntsx is offline  
Old 8th Feb 2016, 5:09 pm   #9
Guest
Guest
 
Posts: n/a
Default Re: avo 8 mk 5

Unless you need NPL (National Physical Lab. Teddington*) levels of accuracy an AVO will do for your day to day measurements. And quite honestly if it is within 20% the circuit is OK (the AVO is much better than that and a joy to use). They can load valve gear a bit but service sheets of the era used AVOs and this error goes away. As to not going back to zero, the meter movement may be a bit sticky, simply tap the meter like an old barometer. Fixing it will cause more trouble than it's worth. A lot of people use 5 3V lithium cells for the 15V.

*If you ever get a chance to visit there, go!
 
Old 8th Feb 2016, 9:59 pm   #10
Oldelectronics
Heptode
 
Join Date: Jan 2016
Location: Nottinghamshire, UK.
Posts: 676
Default Re: AVO 8 Mk 5

If you want a battery 'lanasone' on e bay does one that has the indents on the terminals for my mk3 and were cheap at about £4.95 inc postage I found them ok.try AVO 8 METER MULTIMETER 15v BATTERY BLR 121 AVOMETER. I dont know how the mk5 compares to a mk3 but I have a set of instructions for my mk3 and could scan them if you like?
Oldelectronics is offline  
Old 8th Feb 2016, 10:06 pm   #11
Oldelectronics
Heptode
 
Join Date: Jan 2016
Location: Nottinghamshire, UK.
Posts: 676
Default Re: AVO 8 Mk 5

PS there are others for sale but I went for the £4.95 ones and found them ok when I bought mine?
Oldelectronics is offline  
Old 9th Feb 2016, 9:29 am   #12
mikeald
Retired Dormant Member
 
Join Date: Aug 2011
Location: Cardiff, Wales, UK.
Posts: 97
Default Re: AVO 8 Mk 5

thank you all for the replies...
mikeald is offline  
Old 9th Feb 2016, 10:19 am   #13
mikeald
Retired Dormant Member
 
Join Date: Aug 2011
Location: Cardiff, Wales, UK.
Posts: 97
Default Re: AVO 8 Mk 5

I have just measured a 12 volt battery with my digital meter, and it reads 12.4v.

However, with the avo it measures just over 11v

I am guessing this is not good? Any thoughts on how I can improve on this please?

Thank you
mikeald is offline  
Old 9th Feb 2016, 11:58 am   #14
Oldelectronics
Heptode
 
Join Date: Jan 2016
Location: Nottinghamshire, UK.
Posts: 676
Default Re: AVO 8 Mk 5

It may be worth giving this chap an e mail? http://www.richardsradios.co.uk/avo8.html
Oldelectronics is offline  
Old 9th Feb 2016, 3:29 pm   #15
russell_w_b
Dekatron
 
russell_w_b's Avatar
 
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,684
Default Re: AVO 8 Mk 5

Quote:
Originally Posted by mikeald View Post
I have just measured a 12 volt battery with my digital meter, and it reads 12.4v.

However, with the avo it measures just over 11v
You need to check that the 50uA current through the movement of your AVO is actually reading 50uA. If your movement is not reading correctly on the fundamental scale, you're wasting your time doing anything else.

You'll need a microammeter or suitable multimeter of known accuracy, calibrated preferably, in series with your AVO on the 50uA setting, a 1.5V cell, and a 50k or 100k pot: some means of deriving a steady 50uA supply anyway. Start with the pot at full resistance and crank it up until you read bang-on FSD on your AVO. Then see what the calibrated meter in series reads. The error will be:
[(AVO reading - calibrated meter reading) / calibrated meter reading] x 100 for percent.

Do this then report back.
__________________
Regds,

Russell W. B.
G4YLI.

Last edited by russell_w_b; 9th Feb 2016 at 3:53 pm. Reason: Tautology.
russell_w_b is offline  
Old 9th Feb 2016, 3:30 pm   #16
Mooly
Octode
 
Join Date: May 2011
Location: Lancashire, UK.
Posts: 1,349
Default Re: AVO 8 Mk 5

Quote:
Originally Posted by Thyristor View Post
Which DVMs did you use, Mooly, just out of interest.
They were an old SOAR ME-502 circa 1982 ish and an Escort EDA-210 that's from around 1995
Attached Thumbnails
Click image for larger version

Name:	DSCN0485.JPG
Views:	230
Size:	73.5 KB
ID:	119837  
Mooly is offline  
Old 2nd Apr 2016, 8:28 pm   #17
neonlamp
Retired Dormant Member
 
Join Date: Sep 2010
Location: Tavistock, Devon, UK.
Posts: 84
Default Re: AVO 8 Mk 5

Another check is whether the meter coil resistance is correct. When set to 50uA the resistance should be 2000ohms.
Did you check the 50uA reading yet?
neonlamp is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 11:24 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.