AVO meter repairs.

[Bod]

I have been given an AVOMETER 8, nice condition, last calibrated in 1998 by RS servicepoint, battery compartment in reasonable condition. The RS "Intergrity seal" is still intact.
It does'nt work, needle appears to be seized.
Now I know it will be cheaper to replace with a digital meter, than to have it professionally repaired.
Are there repair guides for these meters?

Bod.

 

[deema]

Give Heme International a call, the chap who owns it, Phil Simpkin in a previous life setup my calibration laboratory and repair centre when I used to run LEM Heme. He serviced just about anything electrical instrumentation and it was regarded in the industry as one of the best. We did everything from meters for power stations, automotive production lines, industrial and domestic. What he doesn’t know isn’t worth knowing.

Alternatively, give AVO a call, when I knew them a number of years ago they were very helpful in supporting their old equipment. People and times may have changed In circa 20 years!

 

[Sideways]

Look inside it. If anything like an Avo 7, they are nightmarishly complex to look at. They are full to bursting with wires and components running in every direction, not like modern circuit boards.
As soon as you see the innards you'll understand why they weigh as much as they do

 

[Old.bodger]

Two thoughts, firstly check that the glass is still correctly in place, the ’adhesive’ that holds it in place gets brittle and I have had some where the glass had dropped trapping the needle. This can be corrected by careful application of silicone sealant with a sharpened match stick and using gaffa tape tabs to pull the glass back up.

Secondly, I think that model has a physical ‘zero’ set on the front panel. Suitable screwdriver will allow adjustment to confirm that the needle is free to move.

Nice ‘old school‘ meters, I prefer mine to several digital meters that I own!

 

[Craig22]

Join or browse UK Vintage Radio Repair and Restoration Discussion Forum . There are many helpful threads and people there on all aspects of all AVO products,

Craig

 

[nickds1]

I've been a UKVRR member for about 10 years and used to have several Avo 8s of differing marks (revisions). There were a lot of different Avo 8 models - the "Mark" number is important, plus there were high-voltage, GPO/BT & MOD variants amongst others. Even, Heaven forbid, braille versions...

The meter movement is extremely delicate and sensitive - you should not interfere with it yourself. It's carefully calibrated using, ISTR, lumps of iron. Don't play with it.

Ask on UKVRR - lots of helpful folk there.

The meter is not great by modern standards - even the cheapest digital meter is better at most things. The Avo is good at doing "true RMS" current and for repairing valve radios etc. where the manufacturer's service sheets give voltages etc. that were measured with an Avo or equivalent - Avos have a very low input impedance by modern standards - 20,000 ohms per volt, compared with a digital meter (DVM) which will be fixed at around 10,000,000 ohms, i.e. it won't vary depending on the range setting of the meter.

When testing old kit a DVM will read accurately but appear too high compared with an Avo as a DVM barely loads the circuit under test whereas an Avo can really pull down voltages. If your service sheet data expects you to be using a 20K ohms/volt meter, i.e. an Avo, that's what you should use.

The corollary of this is that Avos are poor (inaccurate) at measuring high impedance sources.

I have just the one Avo left for exactly that reason.

EDIT: Avos also use old types of batteries for the ohms ranges - these are now difficult & expensive to obtain - you can make your own from coin cells, but it's just yet another annoyance.

(*) A decent modern DVM will also do "true RMS" but to handle non-sinusoidal well you'll need a Fluke/Keysight etc bit of kit. Note that unless you're an electronic engineer, none of this matters much!

 

[deema]

What a great forum, never knew it existed. Thanks for the link.

 

[Bod]

I've been a UKVRR member for about 10 years and used to have several Avo 8s of differing marks (revisions). There were a lot of different Avo 8 models - the "Mark" number is important, plus there were high-voltage, GPO/BT & MOD variants amongst others. Even, Heaven forbid, braille versions...

The meter movement is extremely delicate and sensitive - you should not interfere with it yourself. It's carefully calibrated using, ISTR, lumps of iron. Don't play with it.

Ask on UKVRR - lots of helpful folk there.

The meter is not great by modern standards - even the cheapest digital meter is better at most things. The Avo is good at doing "true RMS" current and for repairing valve radios etc. where the manufacturer's service sheets give voltages etc. that were measured with an Avo or equivalent - Avos have a very low input impedance by modern standards - 20,000 ohms per volt, compared with a digital meter (DVM) which will be fixed at around 10,000,000 ohms, i.e. it won't vary depending on the range setting of the meter.

When testing old kit a DVM will read accurately but appear too high compared with an Avo as a DVM barely loads the circuit under test whereas an Avo can really pull down voltages. If your service sheet data expects you to be using a 20K ohms/volt meter, i.e. an Avo, that's what you should use.

The corollary of this is that Avos are poor (inaccurate) at measuring high impedance sources.

I have just the one Avo left for exactly that reason.

EDIT: Avos also use old types of batteries for the ohms ranges - these are now difficult & expensive to obtain - you can make your own from coin cells, but it's just yet another annoyance.

(*) A decent modern DVM will also do "true RMS" but to handle non-sinusoidal well you'll need a Fluke/Keysight etc bit of kit. Note that unless you're an electronic engineer, none of this matters much!

This is an AVO model 8 Mk V serial number 0013956 or 8
The glass is intact, and in the correct place. I've seen a U-tube that states that if the meter has had a heavy knock, the hair spring can get caught. This meter has a frozen needle, I'm hoping it's a simple fix.

Bod

 

[Phil Simpkin]

Give Heme International a call, the chap who owns it, Phil Simpkin in a previous life setup my calibration laboratory and repair centre when I used to run LEM Heme. He serviced just about anything electrical instrumentation and it was regarded in the industry as one of the best. We did everything from meters for power stations, automotive production lines, industrial and domestic. What he doesn’t know isn’t worth knowing.

Alternatively, give AVO a call, when I knew them a number of years ago they were very helpful in supporting their old equipment. People and times may have changed In circa 20 years!

Thanks for the compliments

 

[Spectric]

Give Heme International a call

I did not think that HEME was still around, I used to use the HEME PR30 current clamp in grey but now they are bright yellow and badged as Fluke.

 

[deema]

@Spectric Heme was bought by LEM and became LEM HEME, the instrument division which included HEME was sold to Fluke who intern were owned by the Danaher Corporation. Fluke rebranded everything Fluke, so Heme as was does not exist. Heme International was started by Phil Simpkin who used to head up the calibration lab in Heme (He built the calibration and repair side of the business from the ground up, it was his baby) . He worked for Fluke after the buy out, he knows all the instruments inside and out.

 

[deema]

@Phil Simpkin holly cow, now that’s a blast from the past. Hi Phil, hope you’re keeping well, and welcome to the forum.

 

[selectortone]

Wow, what a coincidence - I had the plumber round yesterday and needed to check a fuse and I said "I've got my Avo in the dining room" - meaning my multimeter, then I said, "I'm showing my age calling it that...".

I cut my teeth on electronics in the 70s as a test engineer in the QC dept at Penny & Giles in Christchurch. We each had an Avo 8, a Variac, a Fluke digital multimeter and a Tektronix oscilloscope on our bench. We did a lot of MOD work so they all had to be calibrated regularly, by NPL. Long time ago now, but I remember it like yesterday! Happy days!

 

[Spectric]

Fluke rebranded everything Fluke

and put the prices up !!

Where I worked in instrumentation we used a lot of the PR30 current clamps because of there fast response, they were ideal for non intrusive measurement on the common rail diesel injectors where you could not break into the wires without effecting the drive signals and therefore the injection maping.

and a Tektronix oscilloscope on our bench

You must remember the scopes we had to use before the digital storage scope, those ones with the long persistance screens.

Although Tektronix were the scope to have who recals the Hameg scopes, another great name from the past and I still have one, along with a very expensive in the day Tektronix logic analyser that is now worthless.

As for Penny & Giles they made LVDT linear position transducers if I recall correctly and another transducer I used, do they still exist or have they also been swallowed up ?

 

[Spectric]

Should have mentioned that the old AVO's did have a nice wooden case and were like a piece of furniture compared to the plastic and rubber items we use today, also not as good as a digital meter when you get older with eyesight issues, even with the mirrored scale.

 

[selectortone]

As for Penny & Giles they made LVDT linear position transducers if I recall correctly and another transducer I used, do they still exist or have they also been swallowed up ?

They had half a dozen factories in Christchurch making all sorts of equipment for avionics. Their most famous product was the 'black box' flight recorders (actually bright orange) and they also made a lot of other clever stuff that went into RAF aeroplanes and airliners. A lot of the people working there were ex-de Havilland who had had a factory on the old Christchurch airfield making Mosquitos and other aeroplanes during and after WWII. There were a lot of very bright people there who had lots of good stories about the old wartime days. They even designed their own radio telemetry equipment for test flights. Some very skilled guys in the machine shop too, making small runs of machine parts to incredibly high tolerances.

P&G also made wirewound potentiometers and LVDTs and they manufactured conductive plastic faders at a factory in South Wales that were used by the BBC and all the upmarket sound mixing desk manufacturers of the day like Neve.

Curtiss Wright, the American firm who also manufacturered flight recorders bought them out some time ago. The name still exists for some products.

 

[imageel]

I've owned and used many Avo's over the years - I worked for a time at Marconi's in the mid 70's at New St. Chelmsford and latterly at their Avionics division in Basildon. Back then we had a mixture of analog and digital test equipment, the newer scopes were mainly HP models were used for high frequency work and the older mainly valved Tektronix stuff was used for the lower frequency telecoms and broadcast stuff.
A favourite trick used to be to place a sheet of tracing paper between the CRT and the graticule of some old-timers workstation and then watch the following morning the poor fellow head scratching as he tried to adjust the beam focus and astigmatism controls to render it useable.
Of course for me now the boot is on the other foot as my eyesight has got weaker and any micro-electronics work is a real struggle... Ho-Hum!!

 

[Suffolk Brian]

and put the prices up !!

Where I worked in instrumentation we used a lot of the PR30 current clamps because of there fast response, they were ideal for non intrusive measurement on the common rail diesel injectors where you could not break into the wires without effecting the drive signals and therefore the injection maping.



You must remember the scopes we had to use before the digital storage scope, those ones with the long persistance screens.

Although Tektronix were the scope to have who recals the Hameg scopes, another great name from the past and I still have one, along with a very expensive in the day Tektronix logic analyser that is now worthless.

As for Penny & Giles they made LVDT linear position transducers if I recall correctly and another transducer I used, do they still exist or have they also been swallowed up ?

I still have a Hameg 20 MHz storage scope. Must be 25 - 30 years old. Still works, and it never let me down. Got me out of a hole on many occasions. Happy days.

 

[Spectric]

Recently been looking at some of the current instruments like logic analysers and such, the thing you notice is that many are now Pc based and much much smaller. I suppose it makes sense in that if you have a Pc then you have a nice big screen onto which to display any data so you only need the front end to collect the data, a bit like having just the logic analyser pods and no big bulky logic analyser sitting on the bench and not forgetting the obvious we now have data storage in Terabytes rather than kilobytes in a Pc.

 

[MorrisWoodman12]

Well this thread is a trip down memory lane! I remember many of the companies mentioned and some bits of kit. I was less into the instrumentation side than scientific instrument design before going off to industrial ink jet printing and semiconductor lasers.
Who introduced the first storage scope? Was it Nicholet? I do recall evaluating one when at Pye Unicam. I also remember huddling around the old Tek scopes on a cold winter's morning
Great thread
Martin