AVO VCM Mark 3 (Valve Characteristic Meter)

One Item off the Wish List

by MD0MDI
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AVO HF-135 RF Signal Generator - 001

AVO VCM Mark 3 (Valve Characteristic Meter)

I have for some time now been wanting a Valve Tester, I picked up a long time ago well over 20.,000 boxed and mint valves, as well as boxes and boxes of valves with no boxes (over 10,000) of these as well, my early chances to go through them was very hit and miss and I was more interested in creating graphics for this site, anyway it was always a major item on the ‘Wish List’ and I never really thought that I would find one, and especially not a cheap one, but she is a little tatty at first glance…

AVO HF-135 RF Signal Generator - 002
Lift the top cover to see the available sockets.
AVO HF-135 RF Signal Generator - 002
She has signs of age, use, but baring the few scratches here and there she is after all a 'Worker!'

When I first sore this one I wanted it, it looks warn but I was told it was a working unit and having bought stuff off the same person I kind of trusted what he said, and I am glad that I did.

She certainly has that look of being left on a workbench in a corner of an old workshop and occasionally used over many years. She does not smell of being located near to a load of smokers, and the condition has that look and feel of just being old in an old workshop.

She arrived really well packaged up to make sure that nothing got broken, I was a little worried as it weighs around 20kg, but DHL did a great job as they have always done for me, the box arrived 2 days later and was not even dented, it had been taped up with ‘Fragile’ tape and was really well padded out to make sure that the front of the unit would not get damaged.
AVO HF-135 RF Signal Generator - 008
The only issue with the unit seems to be these clear plastic dials that show definite signs of age.
AVO HF-135 RF Signal Generator - 010
Sadly both dials will need to be replaced, something tells me that I will be waiting a very long time indeed.

A quick look over the tester does not show any real damage, just loads of signs of wear due to age and use. The problem ahead of me here is finding good parts, the plastic dials are still very useable and at least intact bar a few cracks, but I may be waiting a very long time before I see any of these come up on eBay.

AVO HF-135 RF Signal Generator - 003
The sockets look to be intact and just need a dam good clean.
AVO HF-135 RF Signal Generator - 004
The rotary encoder looks to be intact, which again can be a nightmare to locate parts.

The Valve sockets are thankfully fairly easy to locate if new ones are required, but involve quite a lot of work. On the other hand the rotary encoder/selector/switch is a deal breaker if broken, and could add a great deal of time to a restoration.

AVO HF-135 RF Signal Generator - 007
A good splattering of paint and grime to be cleaned off.
AVO HF-135 RF Signal Generator - 015
Another good find is an intact meter and glass.

If a splattering of paint is the worst that I will have to deal with then I am on for an easy restoration job here, that’s if I go down that route, sometimes just giving something a good clean and leaving the signs of age intact can be somewhat more like caring for an old friend. A nice find here is also the seeing that the meter is intact is a real bonus, so many meters from old that have damaged glass, which can be a problem trying to locate replacements for nowadays.

AVO HF-135 RF Signal Generator - 017
Everything is covered in dust and grime.

There is a healthy layer of dust and grime in the form of a slightly greasy feeling coating as though someone had sprayed it with a protective film, but there are no signs of rust, at least on the outside anyway, even all the screws look good for it’s age.

So at this point I decided to just give it a quick clean with some ‘Anti-Static Foam’ spray cleaner, one minute later she and she looks a good deal better.

AVO HF-135 RF Signal Generator - 020
A quick Clean makes a lot of difference.

Some soft cloths and a few sprays of anti-static cleaner certainly do make a difference, she is far from looking new, but only wanted to see what was under all the grime and too see if there were any hidden problems. I still have a long way to go with this item, and there are loads to check over before I start a full restoration.

Which Way to Go...

I have a couple of decisions to make with a piece of kit such as this.

  1. Clean Test and Restore
  2. Clean Test and Use

And this is even before I have found some issues when I start testing her.

She needs a good clean, and not just an external spray with some Anti-Static Foam, that can be alright for items that are new and often used, but this is unknown kit, and on top of that it is also has Vacuum Tubes insides, this means extremely high voltages that do not give you any leeway when messing about inside, the voltages inside this unit will kill even the most seasoned engineer working on Restorations, so care must be taken, especially when attached to the mains and while I am on the subject good quality ESD Safe gloves should be warn at all times, and not the cheap ones from AliExpress or some place in China, nearly all of these I have seen fail most if not all Insulation tests and most ESD tests, you cannot afford to skimp here, be safe and stay alive.

Look for these: ‘SKINTX BLK50010-M-BX Nitrile Medical Grade Examination Gloves’, these not only work, but they are recommended by some good known sources.

Before I connect her up to the mains I will need to give her a good strip down, at least so that I can see what it is like inside, looking for leaky capacitors, loose connections, and to see if there has been any previous bodging.

After this we can see about connecting her up to an Isolation Transformer and a Variac, with something like this I may take about 6 hours bringing her slowly up toa working voltage. Unless it has been played with, AVO kit is normally extremely well built, and normally when you remove the covers, even after many years of use, they often look very clean, maybe in this case I am hoping for too much.

AVO HF-135 RF Signal Generator - 021
So watch this space to see which way I go...

So, I am afraid that you will all have to wait, I will update this page with more photos and information on this build along with any useful downloads that I come across to hopefully help others. Please bear with me, I am still far from well and it takes me ages to do simple jobs nowadays, but I will get there…

Useful Downloads for the AVO Mark III Valve Tester

To be uploaded…

Last Updated : 16th November 2022

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