AVO 8 Mk 4 ...

Is it the circuit diagram at

Hi Robin, thanks for that. It would appear to be the correct one. Looks as though you need to pay to become a member, so I will hold off for now until all the feelers that I have out, run dry. It's really annoying because I have owned the meter from new when I was an apprentice, and I have the book, which has the schematic in it, carefully filed away somewhere, but I'm buggered if I can now find it. It is in a box file, but said boxfile is not where I know it should be. Even more annoying is that I have damaged the meter by my own stupidity, so now have the need to fix it ... :-(

Arfa

There may be an outside chance its turned up on alt.binaries.e-book.technical at some time or other.

Whether I'd have downloaded it is another matter, and it would take a while to search my archives.

You could try a REQ: on that group while I try to remember where I put all the unsorted stuff.

That's too bad. I have some old gear I used as an apprentice that have a high value in the nostalgia department. An old EICO 232 VTVM, B&K 1801 freq. counter, Beckman Tech 310 DVM, Amprobe Amp Clamp and some other things that I can't think of right now.

Have you tried:-

And get a log on for the support pages?

They seem to be the sort of company who do product support properly. It might even be worth giving them a call at their head office in Dover.

Have you tried the Vintage Radio Forum?

They have a vintage test equipment forum and there are lots of nice, helpful people on there ...

On the other hand, there's also me ...

In article , Arfa Daily writes

Measured the resistance of the mains?

BTDTGTTS.

Have you tried AVO direct? They still make the Model 8, IIRC.

Not that hard. The overload cutout is a sensitive beast and the adjustment procedure is a little convoluted.

Thanks all. Some useful suggestions there. You are of course all quite correct in that it is very difficult to damage an AVO. This one is now around 40 years old, and it has been in use on a daily basis for all of those years, and has withstood much normal workshop abuse - yes, including measuring the resistance of the mains ! - many times over. It was a very high pulse voltage that caused the problem that I now have. I have recently been working on some pro lighting equipment that makes use of short-arc discharge lamps, and it is important that the running voltage, once they have struck, is correct. They are fed with a 50% duty factor square wave at about 200v p-p, resulting in an average 'AC' voltage of 100V across the lamp. The AVO reads this nicely on either its 100V or 250V AC ranges. When the lamp is being started, however, it is subjected to a pulsed igniter voltage of several kV. When the lamp strikes, its impedance drops quite low, and this swamps the igniter circuit and stops it. Stupidly, I had the meter connected during the ignition sequence, and now, 100V of 'real' sinusoidal AC reads about 35V ...

I am at this point thinking that it is going to be one of the two rectifier diodes, which seem to be "OA" germanium types, but I guess it could also be a fried metal film precision resistor. Needless to say, there is no visible evidence of any problem :-\

Arfa

Dave Plowman (News) used his keyboard to write :

They stopped making it about, oh - two or three years ago. I think too expensive, too complex to make were the reasons quoted.

The last one came off the line in November 2008. This gave rise to simultaneous nostalgia and relief that reference quality meters now weighed less than a sack of coal. ;-)

Thanks Ian. Be appreciated if you were able to have a quick look. Wouldn't have been a problem back in our old TeleMag days. John would have flung an ad in "Help Wanted" for me ... :-)

Arfa

Yes, Meat. It's very frustrating. I cut my 'professional' teeth with that meter, and it has served me faithfully over the years without serious mishap. It is still in weekly use, but not quite the daily use that it once was. For some types of repair, the swinging needle of a quality instrument like this, is so much more appropriate than a digital type ...

Arfa

Its a well known fact that the human eye can gain a rough ideas of what's going on much faster with an analogue display, as it takes longer to read a digital display, although in the end that is more accurate.

I have never felt the need for a DVM or DAM..99.99% of voltage and current readings are of the 'is it within 20% of where it should be' flavour.

The fact is an LCD meter is CHEAPER than a quality moving needle display.

Not better.

They were certainly very expensive last time I saw them for sale - about

Not MK4 but MK3 is here:-

MK4 on ebay but high priced (IMO):-

In message , Arfa Daily writes

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