AVO Transistor Tester TT537

[Radio Wrangler]

Well, I've had a good dig into the transistor testor.

I thought my luck was in on getting home when I read Woodchips' offer of Plessey mains connectors. That allowed me to get power on the thing.

No signs of life, but no smoke. It might be something simple.

Nope. The meter is open circuit.

So the next step is to open the meter, hoping for a simple fatigue break on the end of a wire. Nope, it's the coil winding itself, the burning and open circuit can be seen under the microscope.

If it was really really important I could get some wire and rewind the coil. I've done it before but I didn't enjoy it. Making the jigs needed takes most of the time.

I usually decide about transistors with them in-circuit, so it's no terrible loss. I haven't used a transistor tester in the last 40 years, though occasionally a curve tracer.

But this individual aside, what is it with AVO and their testers? (Transistor and valve) No effective meter protection from a meter company? This machine had metal rectifier packs across the movement. These instruments are easily destroyed by careless use, and they wind up in the hands of the unknowing so frequently.

I'll put a post in the wanted/sale area in case anyone wants bits. I've had my curiosity slaked. I'd not had a look in one of the transistor testers before.

The handles are nice for some future project, I might keep those, and someone with a later but tatty VCM might want the knobs.

David

[Dekatron]

What a pity!

You could always use a Simpson 29T Taut Band meter with an FSD of 25uA and swap the scale as a good replacement. It might even be possible to put the Simpson movement inside the original meter case, but I don't know if it will fit.

My friend Euan MacKenzie, who lives in Australia, made some bolts and a template that can be used to put the Simpson movement into the original AVO Valve Tester meter case after you have drilled two new holes to accomodate the screws that fasten the Simpson movement.

If you don't have time to swap meters you could always sell the two thermistors to anyone who needs them for their VCM163!

/Martin

[Radio Wrangler]

Some photos for anyone interested

Well, I tested it with an AVO!

Then one showing the movement out. The little hex spacers that the scale is screwed to are actually through bolts which hole the magnet to the plastic case.

Finally the site of the Zap!

I used a very obscure 'Elicar' macro lens (1:1) that was made for forensics hand-held on a Nikon D2Xs. Photographing a meter coil isn't particularly easy.

David

[Radio Wrangler]

I don't think a transistor tester would be worth the effort,those Simpson meters are expensive….

Ooo -rrr Martin, you've kicked a few memory cells into action. I have some nice new Ernest Turner meters in the attic, mostly 30uA I think. I'll get them.

Ah, one 50uA one!

I'll need to make a new aluminium backplate but it looks like it might fly. Then there's the scales but they're simple linear ones.

David

[Dekatron]

That looks nice!

As long as the meters both have a 90 degree deflection it is easy to do new scales from the originals in a simple paint program on a computer. When I was making new scales for the Simpson 29T's for the AVO valve testers it took some time as the Simpson meters are 100 degree deflection - that was before I had heard of the software called Galva (which I've never used for more than tests as I was already finished with my scales by then).

/Martin

[WME_bill]

AVO TT537/ CT537. David (RadioWrangler). Your grouse about why no sensible meter protection. I suspect it was a matter of cost. Extracting from my copy of the TT537/CT537 Manual:
The TT537 is the civilian version with a Taylor model 50 meter with no cutout. The Admiralty version CT537 uses an Avo fully sealed meter with cut out which breaks the Lt transformer circuit. This cutout replaces the Lt fuse on the civilian model. (FS2).
This cut out works very well, and has saved my meter so far. Anyway, congratulations on a good job well done. wme_bill.

[Radio Wrangler]

I'm afraid not much has been done beyond the autopsy, Bill. The meter was just popped into the hole to see whether it would fit in with the panel and the case. I'll get some lugs for the Ernest Turner meter tomorrow (they're in my junk box at work) and see if it produces any encouraging signs before I wade into any metalwork. I think I might have to arrange a meter protectin device somewhat better than it has.

So AVO thought it needed protection from sailors, but not from civvies… Ah!

David

[pmmunro]

David/WMEBill,

I think between you you may have answered the question of why AVO didn't provide meter protection without meaning to.

When these testers were made AVO would have repaired a customer's damaged movement for quite a reasonable price; after all they had everything in place to change a moving coil, remagnetise and recalibrate a movement and probably considered it a worthwhile customer service. (Though they would probably have said "a service to our customer" rather than use a managementspeak term). I wonder on what basis it would have been costed? Would anyone have thought there would come a time when pivots, bearings and even enamelled copper wire would be hard to find? Only five years ago Sifam would have made you a movement to specification if you were willing to pay for it.
Did they withdraw the service because old George or Mary retired, because the process didn't make the required profit margin or because it no longer had a suitable image?

The Admiralty would probably have specified meter protection first and worried about cost later, if at all. When at sea on the other side of the world, meter replacement would have been more difficult. On the other hand navy technicians of the time might well have had the personal and technical resources to repair a movement although procedures might have forbidden it.

Fifty years on, the world has changed and whole instruments are considered expendable if they are damaged before their 3 year life span (support duration) elapses , but perhaps more significantly, attitudes to costing are different, possibly with some justification.

I suspect that your range and depth of skills are rare amongst those who will replace you in the workforce when you are retired and it is these skills and many years of intelligent experience which support your interest in old equipment. Thanks too for sharing it on the forum.

PMM

[threeseven]

Yes, we must realise that instruments, even from this era, were never imagined or intended to have a life of 40, 50 or even 60 years. The fact that some of them do still work and or have been repaired and continue to work is a tribute to the design and materials but it's good fortune rather than expectation.

[Radio Wrangler]

I don't think it's a matter of years in this case, the meter would have been fine right up to the point where someone poked the test button with the meter on too sensitive a range. From the heating, though, it looks like the button must have been held in with the meter pegged at the top. Maybe someone thought it was fun to watch a transistor go up in smoke?

It could have happened anytime, but I suppose nowadays more VCMs etc are in the hands of people who don't know how to operate them properly.

I still think that most machines ought to be designed so that they can't be ruined by simply wrong operation of the controls. (I know cars can be driven at walls, but electroonics boxes ought to be properly protected)

David

[pmmunro]

I still think that most machines ought to be designed so that they can't be ruined by simply wrong operation of the controls.

I agree - in fact I'd go as far as to say that the designer has a duty to anticipate common errors and even to protect against deliberate misuse where possible. However, we have to consider how much this is a modern perspective, possibly a technologically enlightened one. Even well trained and intelligent users make mistakes so wherever it is technically and economically possible to provide protection, it should be provided.

With engineering hindsight, you could compare an AVO 8 Mk V against a contemporary Goertz multimeter with electronic protection, or a steam locomotive with an Airbus as examples of what was expected of the operator.

We probably admire products which are designed the way we would have done and clearly you would have the knowledge and experience to design better protection making this failure all the more frustrating.

Originally Posted by Radio Wrangler

But this individual aside, what is it with AVO and their testers? (Transistor and valve)

Martin (Dekatron) probably knows best what the failure modes of these meter movements are, but, yours aside, it seems that many are due to age-related failures rather than misuse. For example, are coils failing open-circuit and is this caused by corrosive flux eroding the wire, wire embrittlement, fatigue failure, corrosion due to damp storage, coils wound too tightly?

Which of these could have been anticipated in 1960? In the case of your TT537, I agree AVO should have done more but customer preferences/expectations, available technology, competitive products and prices, cost/benefit balance of protective measures, as they were then, have all to be considered.

Originally Posted by Radio Wrangler

I haven't used a transistor tester in the last 40 years, though occasionally a curve tracer.

Does anyone still make comparable transistor testers or were they only considered necessary by comparison with valve servicing techniques?

PMM

[Radio Wrangler]

Hmm

Peak make some very handy little transistor and diode testers. But I suspect they are more used for confirmation once a device is removed from its circuit, and for trying to identify a mystery device and find which leg is which. That said, I don't have one because simply looking at conditions in a circuit gives a good clue to which devices are pining for the fjords, and also gives a clue to which may have been taken out in a cascade failure.

The big difference between valve and transistor design lies in how many devices get DC coupled to each other, and so anyone growing up on valves has to learn how to handle the case of an audio power amp, or a bench PSU where devices are tightly interrelated and can fall like dominoes.

Valves have much more solitary lives in comparison, and they also are handily socketed, so testing is a lot easier and gives more focused results. Substitution methods also work well because of the lack of domino effect. Try substituting in a DC coupled amp or psu and you part by part destroy all your substitutes and the thing never works.

I'd hoped for flux corrosion, but I was wrong.

Of course, if the thing hadn't failed, I probably wouldn't have got hold of it.

I don't think I'll ever really have a need for it other than maybe identifying zeners, but I've never had one apart before so I bought it out of curiosity not practicality.

THere are lots of solid state hifi amps out there, some of them quite posh and expensive, but there isn't a market for transistor testers at thousands of pounds a go. You don't read of people comparing the acoustic properties of different date-codes of 2N3055 in Quad 303s. A long-departed friend used to refer to them as "whine connoisseurs"

David

[Herald1360]

Originally Posted by Radio Wrangler

So AVO thought it needed protection from sailors, but not from civvies… Ah!

We used a "scale of robustness" at Racal that started with Engineer Proof, up through Squaddie Proof, Kid Proof, Syph****ed Matelot Proof and finally "Technical Director Proof"......