Avo light meter

Came across this tiny old light meter tucked away in stores. There's a side button to change readings to X5.

Shame the input glass is broken...but it still gives reading.



It's getting on a bit......gives a light source factor for 'gas light'.

They must have had some designer AVO, they're classics in the looks department

What's the light source factor

I presume it's where you derate the reading depending on source

Mikegh said:

What's the light source factor

I presume it's where you derate the reading depending on source

Click to expand...

Zoom in on the last photo...... rating factor applied for different types of lighting.

Ya I saw it took a few minutes to realize what it was

ipf said:

Zoom in on the last photo...... rating factor applied for different types of lighting.

Click to expand...

Im googling luxmeters but I'm not seeing any analogue ones in the results

Presumably they'd have the advantage in some situations that you get with analogue clamps and Meggers that you can see fluctuations quicker

I dunno does that apply with luxmeters,.never used one

Late 40's early 50's according to this, £22 if you want another one;

i have several light meters, various makes, all analogue. rarely used now cameras have it all built in.

Nice Light Meter ?
Their first multimeter was produced in 1923. All dc ranges! Wish I could find one!
They made many different meters and items of test equipment (signal generators, valve testers, even geiger counters for civil defence). Interesting article on Wikipedia if you like that sort of thing.
sold on fleabay recently:

I wonder what the accuracy is like on the old stuff

Did they have calibration back in those days ?

The vintage avo stuff is cheap, investment opportunity I reckon, helps if you know how to repair them

Mikegh said:

I wonder what the accuracy is like on the old stuff

Did they have calibration back in those days ?

The vintage avo stuff is cheap, investment opportunity I reckon, helps if you know how to repair them

Click to expand...

The claimed accuracy in my 1960's Avo 7 manual says, for DC, 1% of full-scale value over the range. For AC 2.5% from 25Hz to 2kHz. You can read the scale accurately because of the blade pointer and non-parallex mirror, so you adjust the position of your head to view from exactly above the pointer.
Yes to calibration, but in the days pre-ISO9001, tended to be MoD, Aviation, Laboratories, some manufacturing industries etc, rather than the average electrician I think ?

There's a vintage MOD Avo calibrator on eBay at the moment, but no idea what it was for!
Avo valve testers go for lots of £££ ?

The other name for AVO is quite a mouthful

All the companies have switched to simple names these days

ipf said:

It's getting on a bit......gives a light source factor for 'gas light'.

Click to expand...

1939 - no - this is an exposure meter - maybe yours is earlier still !

Calibrating vintage test equipment can require quite specialised knowledge. It often goes beyond adjusting a trimmer to get the needle pointing at a particular mark on the scale. The calibration procedures often specify particular instruments and references which might not now be on hand with proven calibration, e.g. to calibrate an AVO Valve Characteristic Meter you need to start out with a calibrated Avometer of the right model. If you use an alternative it is up to you to calculate the effect that might have on the procedure and results.

Repairing moving coil meters, the heart of most analogue instruments, is an art outside the scope of normal electronics practice. It is fine, skilled work equally or more exacting than watchmaking. I consider myself a good precision worker with a sensitive touch but the first two moving-coil instruments I tried to repair, I damaged through heavy-handedness. It felt like using a bulldozer to thread a needle.

The last company offering repairs to the special high-sensitivity movements in the AVO VCMs stopped years ago, so now if they fail (or are damaged through misoperation) one is obliged to modify the circuit to use an available, lower sensitivity alternative, i.e. hack an otherwise beautiful example of vintage test gear.

Vintage light meters can drift as the selenium cell ages. There is usually enough adjustment to bring them back into calibration.